Top Ten Whatchamacallits of Physics

So there's this thing.... it's the rate of change of velocity an object experiences but I just can  NOT remember the word for it.... it's umm.... whatchamacallit... Acceleration!!!!! That's it. Acceleration is measured in m/s^2 and its formula is a= change in V/t. Let's say that a ball increased its speed from 0 m/s to 10 m/s over 5 seconds of time. If we were trying to find the acceleration of the ball, what equation would we use? We would use a=change in V/t. Since the ball goes from 0 to 10 m/s, its change is 10-0 so 10 m/s. We plug this into the top quantity. Because this change occurs in 5 seconds, we plug in 5 for time. a=10/5. The acceleration of the ball is 2 m/s^2.

So there's a rope.... if you put a weight on the end of it, the rope may snap. In order to figure out if it would snap, and which side of the rope would cause it to snap, we have to use these things... they're kinda like labels, but not really. Dang-it why can't I remember?? They're um.. whatchamacallits... VECTORS!!

 

 

In order to determine which side is most likely to snap, we have to draw a line, labeled 'F-net up' pointing upward from the ball (the ball is the weight on the end of the rope). Then, we need to draw a line pointing downward from the weight labeled 'F-weight.' Using a ruler, draw a diagonal line using the F-net up arrow as your guide. Line the ruler up with the top of the arrow and draw a line pointing up to the right and then an arrow pointing up to the left (you can see this in the picture). P.s. make sure you label one side, Side 1 and the other Side 2 so that you have a reference point as to which side, if any, would most likely snap. Drawing a line across and up from the middle of the ball and up to the vector lines on both sides, you can see which side would most likely break. The side with the longer vector is the side that will most likely break due to the tension put on the rope. Vector's also help us understand why boxes go down a slope and a sled slides down a hill.

 

 

 

Well, if you want to go skydiving any time soon and receive extra credit in physics, you have to understand... um.... uh... well.. this is awkward.... what's it called? It explains why it is that a diver speeds up so fast for a long time and then eventually begins to have a steady pace. It's called um... whatchamacallit... air resistance!! Air resistance is the forces that are in opposition to the relative motion of an object through the air. There are 2 things that will increase the force of air resistance: Increase the speed and increase the surface area. The force of air resistance increases as a parson falls through the air because they are speeding up. When someone is falling, their acceleration decreases, velocity increases, and the net force decreases. An important rule about air resistance is that acceleration is directly proportional to force. This means that when acceleration decreases, so does the net force and when acceleration increases, so does the net force.

 

 

So there's this formula that defines why that if a car and truck crash, the same force is impacted on both vehicles. If only I could remember the dang formula... it's umm... it's... whatchamacallit? f=ma. We know that the mass of a big semi-truck will most likely be bigger than the force of a tiny Toyota Camry. When the truck with a larger mass runs into a tiny car, the truck causes the car to accelerate forwards. This acceleration is obviously greater than the truck's acceleration.

Truck --> f=Ma

Car --> f=mA

Both of these equations will equal out, causing the force to be the same for both vehicles.

 

 

So there are two different kinds of velocities. One type is defined by how many rotations it makes in a given amount of time. The other defines the distance it covers in the same amount of time... well... if only I could remember these names for the different velocities. Well, the first one covers rotations.. so that's um... whatchamacallit? Rotational velocity!! Now I just have to figure out the second... this one covers the distance in a given time. It's not rotational so it must be... whatchamacallit? Tangential Velocity!! Lets say there are two cylinders, one large and one small and they are connected by a chain. Since tangential velocity is the distance they cover in an amount of time, the small cylinder has to keep up with the bigger one. Because of this, they have the same tangential velocity. We can figure out which cylinder has a greater rotational velocity by finding out how bug the cylinders are. The smaller wheel has a greater rotational velocity because the smaller one has to spin more times to get to the same distance as the bigger one.

 

 

So there's this reason that physics describes as to why and how an athlete doesn't fall over easily. There's one main principle to it and if you aren't doing it, you have a much greater chance of falling over. This is called... um... really? I can't remember it? its.. ugh... whatchamacallit? Base of Support!!! An athlete is less likely to be pushed over when they keep their legs shoulder width apart because having your legs shoulder width apart creates a lower center of gravity which causes stability due to a wider base of support.

 

 

There's a formula that describes to us why a car takes a long time to fully stop. If only I could remember what it was... I remember it has 2 initials, a 1/2, a quantity squared... it's whatchamacallit... that's right! KE=1/2mv^2. Let's say a car is moving at some speed and requires 10 m to stop. How many meters will it take to stop if the speed of the car is tripled? We can solve this by just plugging in 3v and then using that information to find work.

KE= 1/2m(3v)^2

KE= 9(1/2mv^2)

Work=change in KE

f(d)=change in KE

f(9d) = 9(KE)

This would take 9 miles.

 

 

So there's this thing that helps us understand why a bird isn't harmed when standing on a wire, but they get harmed if they run into both wires on a power line... how is this possible? Something about connecting a... um... what do you call it? We use it everywhere we have electricity... what's it called? um... whatchamacallit... A CIRCUIT!! That's right!! If a bird were to fly through the wires and touch both wires with its wings, the bird would be completing the circuit. When both wings complete the circuit there is a large potential difference so the voltage is increased and this causes the bird to get electrocuted. If the bird just stood or ran into one wire, it would not be completing the circuit so it would be fine.

 

 

 There are only two  more things I have to remember. It's an equation we use to describe why things such as a charged piece of cling wrap is attracted to a ceramic bowl. It's an equation with lots of exponents and looks kinds difficult but as long as you know how to plug in numbers, you're okay! I should be pretty good with figuring out these things by now.... it's um.. whatchamacallit?... oh it's Columb's Law: F=k(q1q2/d^2). When a charged piece of cling wrap gets close to the bowl, the bowl polarizes. Positive charges in the bowl move toward the cling wrap and negative charges move away. The bowl is not charged, it is simply polarized due to the fact that opposite charges attract and like charges repel. Since the distance between the opposite attractive charges is less than the distance between the like, repulsive charges, the attractive force is greater than the repulsive force. This is because of Columb's Law F=k(q1q2/d^2). Because the attractive force is larger, the cling wrap is pulled toward the bowl.

 

 

Okay, one more thing. There's this problem I have, I can't figure out the physic's behind why exactly air bags protect us. I mean I know that the air bag is big and fluffy and it's better than smacking your head on a dashboard... but I just can't remember the formula's that go into figuring out why this happens.... this problem is a doozy because it requires 5 equations!! That's a lot to remember, hence my current problem..... I think that if I think hard enough I'll remember all 5 whatchamacallits!! Well, I believe the first equation is p=mv. I can figure out the second one because it's the same as the first: change in p = p(final) - p(initial). Because the change in p is always the same, this means the impulse is also the same. And oh yeah!! Impulse=f(change in p). With these equations, I am able to find out why airbags are so important!!

When a person sometimes has to make a rash decision to slam on their brakes, he or she would like to know that they have the best safety precautions. No matter how they slam on their brakes, they go from moving to not moving. Because of this, change in momentum is always the same.

p=mv

change in p = p(final) - p(initial)

Because the change in p is always the same, so is the impulse.

J=change in p

If a person had to slam on their brakes, they would want to have a small force on their body because the greater the force, the greater the injury. If there were no airbag, They would be stopped very quickly by the dashboard, making the force very large. A driver would prefer to have airbags because it would take longer for the person to stop moving, causing a smaller force.

J=F(change in p)

J=f(CHANGE IN P)

 

 

 

 

 

 

 

 

 

 



Turbine Blog

When told that we had to build a Wind Turbine, I was not happy. With only a week until exams and final work having to be turned in. I did not have time to worry about building a machine. Well, thanks to google and previously taught concepts, I was able to create a very successful wind turbine.

I knew that in order to get the turbine to display voltage, the amount of coils was crucial. In our machine, each coil had 200 turns, making 800 turns in all. This made the turbine spin very fast, as seen in the video below. The coils make a voltage and when the magnets are close to the coils, the domains line up.

The materials needed to make the turbine were:
water bottle
coil wires
disk magnets
square dowel
round dowel
LED
fender washer
screws
wood for the platform
glue

 

 

 

The water bottle was used to make the turbine spin and cause a voltage. In order for the bottle to form this design, we had to cut the bottle in half, cut out a template for the bottom and top of the battle. When this was done, we plunged a hole through the cardboard with a sharpened piece of a round dowel. This round dowel went from the top of the machine to the bottom. this caused the bottle to spin easily and not fall off of the frame. We made 4 coils, each of which had 200 turns. After these were glued down to a piece of cardboard, we used the fender washers and disk magnets to align with the coils to induce the voltage. To do this, we made sure that the poles of the magnets were all facing the same way. When we attached the loose ends of the coils to a LED, we saw that we had successfully created voltage.

 

In this project, I learned that in order to induce the voltage, we had to make more turns of wire. When the turbine was able to spin faster, the possibilities of the turbine being able to light a light are greater. Sadly, ours did not. I really enjoyed this project. I would do it again in a heart beat!!

 

Magnetic Blog Reflection

Why like poles repel and opposite poles attract.
When a N and N pole are put side to side, they repel because the fields are going in opposite direction so they are wanting to move away from each other. When you put a N and S pole together, they attract because the fields are going in the same direction and are trying to become one magnetized object.

What causes magnetic fields?
Moving charges

What causes the Northern Lights?
Cosmic rays feel the force of earth's magnetic field and pulls the rays toward the magnetic poles of earth and because they are so concentrated on these two areas, you can see the force which is the lights.

How a magnet is weakened
When its domains are jostled by heat and collision

How a compass works
There is a magnet in the compass and its domains line up with those of the earth's magnetic field so the arrow points to the direction of the poles.

How does a laptop charger work?
The charger is AC. It puts energy into a secondary cell by forcing an electric current through it.

How Ferromagnetic materials are magnetized
The domains are aligned

Domain
A group of atoms whose electrons are spinning in the same direction.

Cosmic Rays
Cosmic rays are concentrated on the poles as a result of the earth's magnetic field

How a magnet picks up a paper clip.
1- domains in a paper clip are random. (domain: a cluster of atoms whose electrons are spinning in the same direction).
2- The magnetic has a magnetic field
3- When the magnet is close to the paper clip, the domains of the paper clip align to match the magnetic field of the magnet.
4- The paper clip now has a N and S pole and the N pole is attracted to the S pole of the magnet so they stick together.

Moving charges
A  moving charge feels a force in a magnetic field.

Why do cosmic rays enter at the poles and not at the equator?
The moving charges feel a force from the magnetic field of the earth. this force causes them to spiral around the field lines and follow them into the poles.

How does a credit card machine work?
1- Magnetic strip
2- Code on strip
3- Reader has coils of wire that induce the voltage and current
4- Computer interprets electrical signals and converts them back to the code that's in the magnetic strip

Why do transformers not work with DC?
In order for a transformer to work, there needs to ne an alternating current so that the magnetic fields change. With DC there is only a direct current and the magnetic field would not alternate.

Transformer equations
pV/pT = sV/sT

Power (primary) = Power (secondary)

VI (primary) = VI (secondary)

Motor Blog

Each Specific part of a motor is vitally important in order for the motor to run.
The battery is used as a power source to help create mechanical energy.
The 2 paper clips are used to help carry a current through the battery all the way to both end of the coil.
The coil is the main part of the motor. The coil is the conductor. The inductor is based off of how many turns in the coil there are and if the coil surrounds an iron core.
The magnet provides a magnetic field in the motor

We scraped the armature of the coil a certain way because it determines the way the motor spins. If both sides of the coil were completely scraped, the motor would just teeter-totter the whole time instead of going in a full circle. We strip only one side on one side of the coil and the complete side of the other side of the coil so that when the motor wants to keep going back n forth, it won't let it, and it will keep going in one direction.

An electric current in a magnetic field will experience a force. The coil will experience forces going in the opposite way. The loops in the coil provide a torque and the magnetic field is produced by an electromagnet arrangement called the field coils. The pair of forces created, creates a torque to rotate the coils.

The motor could be used to power any small device. Because the Induction wont be very big, it probably wouldn't power a big device.

Unit 6 Blog Reflection

Charges & Polarization
Coulomb's Law: F= k (q1q2) / d^2
There are two types of polarization: Friction and induction
-friction --> Friction is the resistance of motion when one object rubs against another. Anytime two objects rub against each other, they cause friction. Friction works against the motion and acts in the opposite direction
-induction -->

How does a balloon stick to a wall after rubbing it against your hair?
- when you put a balloon to your hair, the balloon takes away the hairs electrons and causes the hair to be positive and the balloon to be negative. when you pull the balloon away, the opposite charges attract, causing the balloon and the hair to stick together. Because the wall is neutral and the balloon is negative, the wall polarizes causing a greater force. Coulomb's Law says that charges that attract cause a greater force and charges that repel cause a lower force. The net force on the balloon is attractive so the balloon sticks to the wall.

Electric Fields
- A positive charged particle finds itself in an electric field. It moves to the left and increases velocity. Is the electric field caused by a positive or negative charge? Explain. It could be both or a mixture because the positive charge could be moving away from the positive charge or towards the negative charge.
- Something is safe inside an electric case because the metal case creates an electric field that protects anything inside of it causing it to have a 0 net force on objects in the box
- a region around a charged particle or object within which a force would be exerted on other charged particles or objects.
EP/EPD and capacitors
- Electric potential --> total PE/q --> J/c or V
- Electric potential difference --> Change PE / q --> V
- Why can something with high voltage be less dangerous than something with low voltage?
--- Something that has a high voltage can have fewer charges but something with low voltage can have more charges. Total Energy is what is dangerous.
- If a bird were to fly through the wires and touch both wires with its wings, the bird would be completing the circuit. when both wings complete the circuit there is a large potential difference so the voltage is higher and the bird gets electrocuted.
- Voltage --> energy given to each coulomb of charge measured across 2 points

Resistance --> resists the flow of charge --> ohms
Ohm's Law --> V=IR
Power--> P=VI
More resistance --> Longer, thinner, hotter
Less resistance --> Shorter, thicker, colder
2d = 1/4F
1/2d = 4F

Charged --> imbalance of protons and electrons. In order to charge an object we have to transfer charges
Polarization --> A balance of charges within an object. Net charge = 0

Direct current --> Continuous electric current that flows in one direction only.
Alternating current --> flow of electric charge that periodically reverses directions

Parallel circuit--> 1/R total = 1/R + 1/R ... continues to stay on if one light goes out. Voltage is fixed. Resistance is cut in half. Current is added.

Series circuit --> R total = R1 + R2 +R3 .... If one light goes out, they all do. Resistance adds. voltage adds. Current stays the same

Why do bulbs burn when they first turn on? The bulb is cold and the filament is cold therefore resistance decreases which means current is high which means the filament will rapidly heat up and expand.

Total resistance when more appliances added for series --> Goes up      parallel --> goes down
Current as more appliances are added --> Series goes down     parallel goes up
Brightness as more appliances are added --> Series goes down         parallel stays the same
What happens to the circuit when a light goes out --> Series all go out      parallel not affected

How does a fuse/circuit breaker protect your house? Why is a fuse needed? How is a fuse wired and how does it work?
- Homes are wired in parallel so each device gets its own branch. This means each device gets the full voltage of the circuit (120V). it also means that the current of each device is added to the total, so as more devices are turned on, more and more current is drawn. if the current gets too high, it can over heat the wiring and cause a fire. this is what fuses protect from happening. At a certain current level, they will shut off all power from the circuit. To do this they must be wired in series with the rest of the circuit. A fuse blows by melting the wire inside.


Calculate how much it will cost to run a 60 watt light bulb connected to a 120 V source for 1 month if it costs .10 cents per Kwh
60 watts = .06 kw
1 month (30/ month)(24/day) = 720 hours

Energy = power(time)
= .06 kw (720 hours)
= 43.2 kwh
cost = .10/kwh (43.2 kwh)
= 4.32 dollars


Electrons originate from the body
Energy/Electric field moves at the speed of light

Current is a flow of charge. measured in Amps = coulombs/second

R increases    I decreases
Current carrying wire is usually neutral
measure current --> R= V/I
Current decreases and filament increases because when filament increases, resistance increases

Ohm's Triangle

I have had an epiphany! This triangle is a remarkable tool to memorize Ohm's Law. The trick to the triangle is that whichever variable you are trying to solve for, you cover it up and use the resulting variables as they appear in the triangle.
For example: If you want to find V, you multiply I(R)
If you want to find I, divide V/R
If you want to find R, divined V/I
Very glad I found this!

Understanding Voltage

This video provides a great understanding and explanation of how Voltage works. With examples of how to determine voltage using potential difference and coulombs using the equation, you really figure out what voltage is all about. This video even touches on the subject of currents which is used to determine voltage in a wider base of knowledge.

That Dang Mouse Trap Car!

Speed: 3.75 seconds
Place: 3-4th

 

Body: Mouse trap --> When the mouse trap is set off, the force of the snap will help project the car forward and give its acceleration.

Wheels: 4 CD's of the same size --> The wheels will be attached to the lever arm and will help the car move stabile and smooth.

Axels: 2 hollow pens --> these two hollow pens will be attached to the body of the car and when the lever arm is snapped forward, the torque will cause the rotation and the axels to spin forward.

Attached to the body: Eye hooks --> the eye hooks will be drilled into the body and provide a place to put the axels that will help stabilize the rotation and smoothness of the axels while spinning.

Lever arm: 2 hollow pens --> the lever arm will be attached to the spring of the trap and when pulled back and released, the lever arm will cause the car to rotate. (Torque)

 

Newton's first law, which is an object in motion stays in motion, or an object at rest stays at rest, really came into play in this project because many, many, many, times the car was stopped by an outside force. This force was, the mouse trap car. We had a lot of trouble with the string repeatedly getting stuck in the eye hooks attached to the mouse trap and causing the car to stop. After we got the eye hooks smoothed out and wrapped around the axel neatly, the car stayed in motion, resulting in it going farther than 5 meters.
Newton's second law, which is F=ma, really made itself known when we tried to race the car. The string we used was a very big part of getting our car to go so when we shortened the string, the mass of our car decreased and it made the car accelerate faster. So little m, big a, caused for a great force on the car.
Newton's third law, which is for every action there is an equal and opposite reaction, came into play when our lever arm was pulled back, and let go. When we would do this, the action of the mouse trap snapping down on the car caused a force that projected the car forward. When there was an action on the lever arm, there was an action on the car which caused it to go.
Rolling friction & sliding friction. We had a lot of trouble with getting the friction taking place on the car to cooperate with us. Our first problem with friction took place when we tried to put the wheels together. The wheels were so wobbly and uncontrollable, we had to figure out how to balance them out. Even though we put balloons on the back wheels, the car was still too wobbly. In order to make the wheels stay in place, Mr. Rue gave us the idea to glue two pieces of wood to the front and back of every wheel and drill a hole in them the size of the pen so that they could fit better and more snug. With some miscalculations, a few of the wheels were still wobbly. This is when we got the idea to just super glue the wheels to the axel so that they won't move around the axel at all. This is when the wheels finally worked! This problem with friction was both a pain in the toosh and a saving grace because when we stabilized the wheels, the car worked.
With a lot of research, we got the idea to use 4 CD's of the same size for wheels. The only problem we had with the wheels was that they were too wobbly and needed more friction. With the help of some balloons on the back wheels, wood, and super glue, the wheels worked just fine. I think the idea of using to same size wheels was a good decision. They weren't really big and they weren't too small.
The energy of the car was greatest in the middle of its path. I think this is the case because the potential and kinetic energy was balanced. Since potential energy is greatest at the beginning of its path and kinetic energy is greatest at the end of its path, PE and KE balance out in the middle of the path and causes a stable amount of energy.
We put our lever arm together with the normal sized, hollowed out pens. I would say that the length of our lever arm was close to a foot, maybe a little less. Our lever arm worked really well. The only difficulty we had with it was the string attached. We had to change the length of our string probably 5 times. The first time it was too thick, the second time it was too long. The third time it was too short, then the fourth time it was too long. The fifth time we ran the car, the string was getting too frayed and getting stuck in the eye hooks so we decided to try another type of string and keep it the same length.... Hallelujah it worked! The length of the lever arm worked really good with the size of our car. It projected a great amount of force and gave the car a great push to get past the 5m line!
Rotational inertia came into play with the lever arm. When the lever arm went back into its normal position and the mass was farther away from the axis of rotation, the velocity was slower. The Rotational velocity was higher when the lever arm was pulled back because the mass was closer to the axis of rotation. This causes the amount of rotations increase. The tangential velocity stayed the same throughout the entire ride because the rotational velocity had to level out to get to the 5m in the same amount of time.
We can't calculate the amount of work because the force and the distance are not parallel. We can't calculate the PE and KE because they are always different. We can't calculate the force on the spring because everyone's ways of setting off their car were different and we all had different cars.
The only major difference that we put on the car was the lever arm with the pens. We originally were just going to attach the string to the trap and pull it back. What prompted the change was that it wasn't enough force to project the car.... and Abby told me =)
The major problems we had was the lengths of the string and the unstableness of the wheels. We fixed the string problem by just doing some trial and error. Sometimes it was too long and sometimes too short. It took a lot of patience to find the right length. We fixed the wheels problem by gluing pieces of wood on both sides of the wheels and drilling holes that fit through the sides of the axel to make them more snug. Then we glued the wheels to the axels and just focused on the rotation of the axels.
In order to make the car go faster I would put together a stronger lever arm that could more quickly project the car with a greater force. Our lever arm was a little bendy!

Unit 5 Blog Reflection

Work & Power

Work = force(distance)
    - FORCE AND DISTANCE MUST BE PARALLEL TO HAVE WORK
When determining distance, only look at the height from top to bottom. STEEPNESS DOESN'T MATTER!!!!!!!!!

STEEPNESS. DOES. NOT. MATTER.

 

 

 

 

 

 

Work is measured in joules!

Practice problem: If a 600 N person walks up stairs that are 4m high (total height as shown in the picture below), how much work is done?
w=fd
w=(600N)(4m)
w=2400 J

If someone were to walk up 3 flights of stairs, and then later in the day go up an to the same third floor (force and distance are the same and parallel,) the person would use the same amount of work both times. If force and distance are the same and are parallel, it does not matter how the person got there, they have the same work.

Power= work/time
In order to determine power, we must first find our work and divide it by the time it to took to get that amount of work.
Power is measured in watts.

Work and Kinetic Energy

Why do airbags keep us safe?
KE=(1/2m)(v)^2
Change in KE = KE final - KE initial
Change in KE=work
Work=fd
Work=(small)f((big)d) with an airbag
Work-(big)f(small)d) without at airbag
Work airbag = Work dash
Airbags increase distance over which force is applied. Since work is the same, increasing the distance lowers the force. Less force means less injury!

KE=(1/2m)(v)^2
PE=mgh
Change in KE =work
Work, KE, and PE are all measured in Joules!

When plugging in numbers for PE, note that m is the mass, g is the gravity, and h is the height. However, mg= force which is measured in N.

Practice Problems:

1) U-Haul truck beds are 1m high. The ramp is 3m high. you are trying to load a 30N box.
    a- How much work will it take to get the box from the ground into the truck
                 w=fd
                 w= (30N)(1m)
                 w= 30J
    b- How much potential energy will the box have if it was just lifted up to the deck?
                  Work=PE
                  PE= 30J
    c- How much PE will the box have at the top if it goes up the ramp?
                  PE=mgh
                  PE=30N(1m)     *because the height is still 1m even though you use a ramp
                  PE=30J
 2) You put 200J of energy into lifting a box using a pulley, but you only got out 150J of work.
      a- How efficient is this machine?
          efficiency= work out/work in
                          = 150J/200J
                          = 3/4 %
                          = 75%
      b- Does this violate the conservation of energy law?
           No because energy is never lost, it is converted into another form of energy such as heat.

3) A car is moving at 20 m/s speed and requires 10m to stop. How many meters will it take to stop if the speed of the car is 40 m/s?
          KE=(1/2m)(v)^2
               = (1/2m)(2v)^2
               = 4(1/2m)(v)^2
          Change in KE=work
          Work=4(original)
          Work= fd
          4(work)=f(4d)      * force is the same because of the same brake pads
          Original distance= 10m
          4(10m)=40m
          40 M to stop the car if the speed is 40 m/s
*Raising an object twice as high gives the object twice the PE because PE=mgh so if you double the height but the force is constant, you will double the PE.

4) a 10 kg ball is on the top of a 4m ladder. If it falls off, what is the speed that the ball will have just before it hits the ground?
   PE=mgh
        =10kg(10m/s^2)(4m)
        = 400J
    KE= (1/2m)(v)^2
         = (1/2)(10)(v)^2
         = 5v^2
   400= 5v^2
   400/5 = 5v^2/5
   80J= v^2
   v= square root of 80 m/s
    
5) If you start out at the top of a roller coaster with 500 PE, what will be the PE at the bottom of the hill?
    Top: PE=500J    KE=0J
    Bottom: PE=0J    PE=500J

6) If you were to jump off of a cliff, you would start out with a maximum PE and minimum KE. As you fall, your PE decreases and KE increases until you get to the bottom where PE=0J and KE= the amount that PE started with.

Conservation of Energy

KE and PE relate in the fact that when one goes down, the other goes up, but they always equal a specific total
Example: PE =100J   KE= 0J............. But when PE= 50J   KE= 50J to equal out 100J when added together. This is how energy is conserved.

When a ball is about to hit the ground, the KE is at 9000J and it began with 12000J of PE. How much PE does it still have?
Total energy=KE+PE
12000J=9000J+PE
3000J=PE

Energy can never be lost!! It can, however, be transferred into another form of energy such as heat, sound, and light.


Machines

Machines are used to help carry or move an object easier. However, the work is still the same. A ramp increases the distance which decreases the amount of force needed to do the same amount of work.

work in =work out
f(d) = f(d)
Larger distance means less force needed.

Why do bolt cutters have such long handles but such short blades?
work handles = work blades
small f (big d) = big f (small d)

If you have a 4 string pulley and you pull a 1600 N weight, how much weight are you actually pulling?
work in= work out
work strings = work pulley
fd=fd
f(4m) = 1600N(1m)
f = 400 N

What is the point of using a machine if it doesn't multiply your work output?
Because it can multiply your force or distance

It is easier to push a box up a ramp opposed to picking it up because the distance is longer with decreases the amount of force needed to move the box.

You can never get more work out of a machine than you put in because that means energy would somehow be created and that is impossible.

Efficiency = work out/ work in
Efficiency can never be greater than 1 or 100&


At the beginning of this unit, I started out really understanding work and power but when we got into potential and kinetic energy, I was 100% lost and I'm sure it showed on my quiz grades. Tonight while going over past quizzes and understanding the answers, I really grasped onto the concept of KE and PE. I am kind of worried about the test because I feel like when I get all of these questions put onto assignment, I forget everything and can't figure out how to put it all together. For the most part, I believe I will be okay, I just need to remember which equation go with what types of problems.

Work Smarter Not Harder

I really liked this video because it is easy to follow, shows demonstrations, and is fun! But actually quite annoying at how it sticks in your head, but that could be a good thing. This video constantly reminds us that when we use a machine, the machine does NOT make the object weigh less or change really anything about the object. All machines do is make an object easier to handle and/or move. This is an essential idea when it comes to understanding machines. Work smarter, not harder!!

Energy, Work, Power Resource

This is by far one of my favorite videos so far! While watching this video, it reviewed everything we went over in class from equations, units, and demonstrations. I really understand how Work and Power well..... work! and this video helps that. Even though it is an intense subject, this video truly informs and educates the listener. Great video!

Unit 4 Blog Reflection

                                                  Rotational & Tangential Velocity
                          -Rotational velocity: The amount of rotations in a given time
                 -Tangential velocity: Distance an object covers in a given amount of time

One of these gears has 12 prongs and the other has 8 prongs.

Which gear has a larger rotational velocity?

The smaller gear has a larger rotational velocity because it has to go in a full circle way more times than the bigger one to cover the same amount of distance as the bigger one.

Which gear has a larger tangential velocity?

This is a trick question!! Both of these gears cover the same amount of distance in a given time. If these gears had to cover a distance of one mile, they would both get there at the same time, the smaller gear would just have to move faster to catch up to the bigger gear that has more prongs.

 

 

Explain how the shape of the train wheels keeps the train on the track.

Do you see how the wheels are bigger toward the inside and smaller towards the outsides? The wheels are designed this way so that they can self correct on the tracks. the wheels have the same rotational velocity but different tangential speeds depending on where the wheels are on the track.

 

Rotational Inertia

 

Why does a solid steel ball win a race down an inclined plane, and why does the hoop lose?

Imagine a solid steel ball. It's heavy, there is no empty space and the mass is all pushed together. Now imagine a hoop. Hoops have zero space in the middle of it. The reason why the solid ball wins is exactly because of this reason. The steel ball's mass is all cultivated in the middle of its rotational axis, when a hoop has 0 mass in its rotational axis. When an object has a great center of mass, it goes faster than an object that has less.

 

 

Will you go faster or slower with your arms held out while spinning?

If a diver jumped off of a board and into a pool and they wanted to gain speed, they should pull their arms in. By doing this, the diver increases their velocity which makes them spin faster but as soon as their arms go out, their velocity decreases making them slow down. This happens because when they are pulling in their arms, they are pulling all of their mass into their center of gravity. This is also why people tuck in their bodies while doing a flip so that they can gain speed.

 

 

Conservation of Angular Momentum

 

Write and label the equation for angular momentum

(Rotational Inertia)(Rotational Velocity) = (Rotational Inertia)(Rotational Velocity)

(20)(2) = (2)(RV)

40/2 = 2RV/2

20 = RV

 

Angular momentum before = Angular momentum after

 

Torque

-Causes rotation

 

How does a meter stick become balanced on a table?

A meter stick is balanced when its center of mass is over its base of support.

 

Demonstrate a two ball scale equation

Counter clockwise torque = Clockwise torque

(Lever arm)(Force) = (Lever arm)(Force)

(1m)(90N) = (3m)(F)

90Nm / 3 = 3m(F) / 3

30N = F

30N

 

 

 

 

Where is the best place to put a doorstep and why?

On the outside of the door because it gives a greater torque and has a longer level arm.

 

Two ways to change torque

- change lever arm

-change force

-change both

 

Center of Mass/Gravity

 

 

 

Why do we have more balance when we bend our knees and spread our feet farther apart?

Because we lower our center of gravity and get a wider base of support.

 

 

Why doesn't the Leaning Tower of Pisa fall over?

Because its center of gravity is over its base of support.

 

 

Why do we lean forward when wearing a heavy back pack?

We lean forward to balance out the weight added to our bodies. When we lean forward, our center of gravity moves so we lean forward to keep our balance and have our center of gravity over the base of support.

 

Centripetal/Centrifugal Force

 

Centripetal- Pushes you toward the center of the object

Centrifugal- a fictitious force that DOES NOT EXIST

 

 

Why do clothes get drier in the spin cycle of the washing machine?

The water goes through the holes because there is no force on the water. Because of this, the water has a straight path so it shoots out of the holes.

 

What I found most difficult....

In this unit I really struggled with understanding torque and centripetal force. Both topics had many aspects to them that really didn't click with me. Before the test, I thought I understand a little better but when I got to the question about balancing a ruler, I blanked. But, I did get a better understanding of centripetal force when we constantly went over it. The only thing is that I feel like I still don't understand it that well, I just memorized what to say.

 

Effort, Problem solving skills....

During this unit, I do believe that I tried hard. I constantly asked questions when I needed to and I helped my table members as much as I could. A few times I came in before quizzes to ask Mr. Rue to clarify on a few topics and wound up getting really good grades on quizzes. On the test, I got my first 5/5 on the problem solving section. I really understood what to do and how to do it. I am very bummed about my grade which hurts because I believe I tried very hard. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

How to find the mass of a meter stick without using a scale!

If a meter stick was not balanced on the edge of a table had a torque, what would it look like?
                                       
                          |____| <-- level arm
           --------------------------- <-- meter stick
                           |       /\ <-- center of gravity
                           | <-- force
This meter stick has a counter clockwise torque, moving to the left. The level arm is placed between the force and the center of gravity.

Now the meter stick is balanced on the edge of the table. What do you know about the relationship between the edge of the table and the center of gravity?
           |  <-- Force
_____ |___________________
           |  /\
           | <-- Force       
Force goes up the same amount it is being pulled down. For an object to be balanced, the object on wither side of the center of gravity must have the same mass. The Counter clockwise and clockwise torque must be equal.


Now watch how the balance point changes when the 100g mass is added to the end of the meter stick. Draw a picture and label the forces and level arms that are causing the clockwise and counter clockwise torques.
     100 g
     _____________________
            /\
The center of mass of the meter stick does not change, but the center of gravity does in order to balance out the added weight.

When we first began to plan out how to find the mass of the meter stick, we were beyond confused!!! To get started, we found where on the meter stick the stick was balanced with the 100 g weight on the end of the stick. We found that it was balanced at 29.5 cm.
In order to convert our 100g into mass we move the decimal to the left one place to get .1 kg.
9.8 is gravity and to convert that, we move the decimal over one place to the left as well.
In order to find the mass of the meter stick, we need to use the angular momentum equation which is, (level arm)(force) = (level arm)(force)
           before                         after
And to find the official mass, we use the equation w=mg

Now to solve,
29.5 cm = .295m
(29.5)(.98) = (20.5)(force)
28.91 = 20.5x
------     -------
20.5      20.5

x = 1.41 N

w=mg
1.41=m(9.8)
-----  --------
9.8      9.8

m= .143 kg 

When trying to figure out how in the world we would find the mass of the meter stick, we stared long and hard at it. We found the center of mass of the meter stick which was 50 cm and then the mass of gravity with the weight on it which was 29.5cm. A key detail that we learned was that just because we added the weight to the stick, the center of mass of the meter stick DOES NOT CHANGE. For the meter stick to be balanced, there must be a counter clockwise and clockwise torque that are equal. The lever arms are located where the center of gravity is to the downward force, and then from the center of gravity to the weight at the end of the stick. The mass we calculated was .143 kg and the real mass was .142 kg.
                                 .3m            .2m
                              ____________________
                              |         |                              |
____________________________________
                              |         /\                            |
             --> 50 cm |                                        |  <-- .98 N  Gravity
                   Center of mass

Another way of thinking about Torque

This is a great way of understanding torque in an in depth demonstration with its effect on lawnmowers. I chose this video because it is not a boring little video with equations and blah blah blah... we do that enough in class. When I think about torque, I don't think about lawnmowers or how it helps cut our grass. I enjoyed watching this video and learned a lot from it because I now have a deeper understanding on something that has been around for decades!

Angular Momentum

Mostly refer up to :45....
I chose this video because it explains the idea of angular momentum with just demonstrations. When the guy in the beginning of the video is on a spinning chair, he starts out holding weights and his arms are out along with his legs. When he pulls his arms and legs in, he gets noticeably faster. This happens because when an object is closer to its axis of rotation, it has a smaller inertia and a faster velocity opposed to when it is farther away from the axis of rotation.
The formula for angular momentum is
(ROTATIONAL INERTIA)(rotational velocity) = (rotational inertia)(ROTATIONAL VELOCITY)
Inertia is measured in mass so when an object has more inertia, it has more mass, which makes it harder to move. When something is farther away from the axis of rotation it has a higher rotational inertia and a lower velocity. When something is closer to the axis of rotation, the inertia is smaller and has a higher velocity.
This video brilliantly shows angular momentum.