Unit Four Blog Post

There were many things that we learned during unit four, they were, rotational inertia, rotational and tangential velocity, conservative of angular momentum, torque, and centripetal/centrifugal force.

Rotational Inertia
Rotational inertia is the property to resist changes in motion (spin). Rotational inertia is what helps determine how many flips you can do on a trampoline, or how many spins an ice skater can prefer. If your arms are close to your body (axis of rotation) the more spins you will be able to preform.

In this diagram, the two meter sticks have two different rotational inertias. The meter stick with the weights next to the end will have a higher rotational inertia than the meter stick with the weights near the middle will have a lower rotational inertia because most of the mass is near the axis of rotation, therefore easier to spin.

Rotational and Tangential Velocities

Tangential speed is the speed of something moving along a circular path. For example on a merry go around, the person closest to the axis of rotation will have a lower tangential speed than the person on the far outside of the merry go around, however they will both have the same rotational velocity because they both will have gone around a complete time at the same time.

 By looking at these two diagrams you can see that the tangential speed increases as you move farther from the axis of rotation however the rotational speed stays the same the whole time. 

Okay so in this example the outside must travel the same distance as the inner merry go around in order to keep the same rotational velocity. 

 Train wheel are designed with tapered wheels wider on the inside and narrower on the outside. Thus all parts of the wheel have the same rotational speed. But the wider part has a greater tangential speed. This difference causes the wheels to curve when the wider part is on the track. When the wider part is on the track it causes the train to self correct its self and get back in the middle!

However gears do not work like train wheels in fact they are the opposite, in most cases the rotational speed is different while the tangental speed is the same.

Conservation of Angular Momentum

The conservation of momentum/angular momentum is equal to the total momentum before to the total momentum after. 

Angular momentum is based off two things,

• Rotational inertia and
• Rotational velocity

Angular momentum before=Angular momentum after

Rotational inertia(Rotational velocity)BEFORE=Rotational inertia(Rotational velocity)AFTER

 

When you go from curled into a ball from stretched your rotational inertia will become higher than before and therefore decreasing rotational velocity.

Rotational inertia and Rotational velocity are directly proportional.

Torque

Torque causes rotation and torque=force(lever arm) a lever arm is the distance from the axis of rotation to the point of contact.  The larger the lever arm the less amount of force there is required and vise versa. AND force(lever arm)=force(lever arm)

As you can see the wrench with a larger lever arm will have a smaller force required than the wrench with the smaller lever arm.

All objects have an average position of their mass, and that is know as their center of mass. Center of gravity must be within base of support or it will fall over.

In this diagram we can see that the people have to adjust their base of support in order they don't fall over.

Counter clockwise torque=clockwise torque 

BALANCE 

In order for something to be balanced, the torques must be equal and opposite,  the center of gravity must be in between the base of support, and the larger the base of support the easier it is for something to become balanced.

Centripetal and Centrifugal Force

Centripetal force is a center seeking force, centrifugal force does not exist it is the concept of a center fleeing force BUT doesn't exist.

The reason we don't fall out of a roller coast when it goes upside down is because the centripetal force pulling towards the center is not a strong as the force pulling the people forward or green arrow.