In this unit I learned how to apply information to formulas and I really learned how to label vectors which I am thrilled about. This unit has been the easiest for me to grasp for some reason. I am more confident to go into the test on this unit than any others this year.
Action/Reaction Pairs
Newton's Third Law- Newton stated that every action has an equal and opposite reaction making the forces the same.
If a train ran into a parked car, the car would push the train just as much as the train would push the car. The car would have a greater acceleration because the truck has a bigger mass so when it hits the car the truck doesn't accelerate that much, but when the car gets hit it has a bigger acceleration because the car has a smaller mass. F = aM F= Am (don't mind the uppercases)
If you held a book above you head
- The book would push the person down
- The person would push the book up
You can tell if something has an action/reaction pair if the reactions had the same verb, only opposite
ex: dog pushes cat, cat pushes dog = action/reaction pair
hand pushes book, book pulls pen = not an action/reaction pair
Tug of war/Horse and buggy
Winning a tug of war game strictly depends on the amount of friction to the ground. If two teams were pulling on opposite ends of the rope and one team is wearing a pair of socks and the other side are barefoot, the barefoot team would win because they have a greater friction to the ground opposed to the team with the socks which causes no friction.
Horse and Buggy
----> Horse pulls buggy forward
<---- Buggy pulls horse forward
----
______ /
| _____| --|---|-------|---|----/
---> buggy pushes ground forward <------- horse pushes ground backward
<--- ground pushes buggy backward ------->ground pushes house forward
The horse pulls the buggy with the same force the buggy pulls the horse with. We know this because of Newton's third law that says that with every action there is an equal and opposite reaction. The horse and buggy actually move forward because the horse pushes on the ground harder than the buggy.
Forces in perpendicular directions
^
| / 14.1 kgm/s
10 | /
20 Kgm/s (x) | /_____ >
() ----------------> (x) = 10
() ------10------->
|\
-10| \
| \ 14.1 kgm/s
y before- 0 kgm/s
x before - 20 kgm/s
y after - 10-10 = 0 kgm/s
x after - 10+10 = 20 kgm/s
______________________________________________________________
We know why a box goes down a slanted ramp because of vectors. The bottom of the ramp is the f-weight and we draw perpendicular vectors and draw a line going down between the vectors. This is called the f-net. The line going up toward the top is the f-support. The direction the f-net is pointing is the direction the box will go.
We can determine which side of a rope would break by using vectors. We draw a straight up and down arrow where the ball is. The bottom arrow is the f-weight and the up arrow is the f-net up. Now we draw parallel lines from side 1 and 2 to the ball. Once we get those we need to label the 2 tensions by using dotted lines. We determine which side will break based on which side is longer.
Gravity and Tides
Universal gravitational force - F = G (m1m2) / d^2
(7x10^-11) (4x10^20) (8x10^16)
--------------------------------------------
(2x10^10)^2
(7)(4)(8)
----------- = 224/4 = 56
2^2
(10^-11)(10^20)(10^16)
------------------------------
(10^10)^2
F= 56 x 10^5
F= 5.6 x 10^6
Spring tides- higher highs
Neap tides - lower lows
Greater the distance from the center of the earth, smaller the mass and force
moon 20 earth 5 difference in force is greater than the moon
Tidal bulges are caused by differences in force by opposite sides of the earth
double --> 1/4 of force
triple --> 1/9 of force
quad. --> 1/16 of force
half --> 4 times force
1/3 --> 9 times force
1/4 --> 16 times force
Momentum
no matter how a person falls, they go from moving to not moving. Therefore change in momentum is the same no matter how it is stopped. change in p = mv and change in p = pfinal - pinitial
since the change in p is the same, the J is also the same. change in p = J
steel cables are more dangerous that elastic ropes because they have no give. if the time is shorter for force, the more dangerous. this is less safe for the climber opposed to an elastic cable that increases the time for the falling climber and has a smaller force. J= f delta T and J= F delta t
Conservation of Momentum
stick together - ptotal before = ptotal after
mava + mbvb = ma+b (vab)
Don't stick- ptotal before = ptotal after
mava + mbvb = mava + mbvb
Bouncing causes two forces so it is safer for a policeman to wear a vest so that the bullet will stick because one bounce is one force and that is less injury.
if something changes its velocity it will change its momentum but not the law because that would have to change the whole system, not just one aspect.
When I faced troubles in this unit I just mainly asked questions. This unit was pretty straight forward so it was easier to understand. Having other students explain was also useful and I liked explaining because it gave me assurance.
My goal for the next unit is to improve my quiz scores. I need to pay more attention to detail opposed to just the basics such as tensions, f-net, f-weight, etc...
I really enjoyed this unit!!!!
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