Unit 4 Reflection

This unit has been all about centripetal force and rotation. I found it to obtain a lot more information in a shorter amount of time to learn it than most other units this year. I believe that I had most trouble understanding the concept of center of mass, but am now able to understand it due to the review questions my class made. I think that I could have been more thorough when answering homework questions in this unit, that would have helped me understand the center of mass concept as well as the other concepts better and in a shorter amount of time.

Rotational/Tangential Velocity:
Rotational and tangential velocity are two terms determining speeds in rotational object. Rotational velocity is measured in rpm (rotations per minute) and determines the amount of rotations an object has every minute. Tangential velocity is the determined by distance over time an object rotates. If an object such as a carousel is spinning at a certain velocity and one person is near the axis of rotation while his friend is at the edge of the carousel, they would have the same rotational velocity but a different tangential velocity. The boy in the middle would be going slower than the boy on the outside because it takes less time and less distance to revolve around the axis of rotation. The boy on the outside has to have a greater tangential velocity so that he can have the same number of rotations as the boy on the inside of the carol. Another example is two connected gears that can be rotated by a handle connected to one. If these two gears are different sizes but are connected, the tangential velocity of the two will be the same and the rotational velocity will be different. If they have the same tangential velocity then it would take the smaller gear more revolutions to go the same distance as the larger gear.

Rotational Inertia:
Rotational inertia is the property of an object to resist changes in rotation. More mass does cause more inertia, but an objects rotational inertia is dependent on where the mass is located. When the mass of a rotating object is located nearer the axis of rotation, there is less rotational inertia making it easier to spin. When a dancer is turning in forte, she repetitively pulls her arms and leg into her body to spin faster, but then spreads her arms and her leg out to slow down.

Conservation of Rotational Momentum:
The Conservation of Rotational Momentum states that the momentum of a rotating object is determined by the rotational inertia (RI) multiplied b the Rotational velocity (RV) so RI x RV=P. Also, the momentum of a rotating object before is equal to the momentum of the rotating object after, P before= P after. Therefore (RI x RV) before= (RI x RV) after. If there is a large rotational inertia and a small rotational velocity before then there is a large rotational velocity and a small rotational inertia after, RI x rv= RV x ri. This podcast helps to explain what the conservation of momentum is and how it works:

Torque:
Torque is what causes rotation, it is determined by the force(f) x the lever arm(la). When a force is applied to an object farther from the axis of rotation the torque is larger, so the torque is directly proportional to the force and the lever arm of an object. In order for an object to be balanced the clockwise and counterclockwise torque must be equal, so (f x la) clockwise=(f x la) counterclockwise. This also means that is the force is large and the lever arm is small on the clockwise side the the force will be small  and the lever arm will be large on the counter clockwise side, (F x la)clockwise= (f x LA) counterclockwise.

Center of Mass:
The Center of Mass is the center position of all things mass. When the center of mass of an object is above the center of gravity, which is when gravity acts on the center of mass, it is balanced. The taller an object, the taller the center of gravity and the lower the center of mass the more balanced an object is. An example of this is a tight rope walker, he would carry a long drooping stick when on a rope to increase the lever arm and make the force smaller so that he would be more balanced. This can also be applied to a wrester, when they squat down and spread their knees they make their center of mass closer to the ground and create a larger base of support so that they are harder to push over.

Centripetal Force:
Centripetal force is the center seeking force that keeps you going into a curve. This is the only force acting on you, many believe that centrifical force is a center fleeing force that pushes you outwards but this force is fictitious and the reason you move outward is due to Newtons first law which states that an object in motion want to stay in motion and an object at rest wants to stay at rest, so when your car turns right your body wants to continue left. Centripetal force is what keeps a satellite in orbit, however there needs to be just enough initial velocity to get the satellite to continue in orbit otherwise it will crash into the earth or fly out into space.