-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.
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