Unit Blog 4

This unit we learned about Torque, center of gravity, base of support, rotational inertia (more and less), angular momentum, tangential velocity, rotational velocity, centripetal and centrifugal forces.

Tangential velocity and Rotational velocity
Tangential velocity deals with distance: so if you were on the inside of a merry-go-round you would have less tangential velocity than someone on the outside.
As for gears: gears have the same tangential velocity (because they cover the same distance per time) but different rotational velocity (because one has a different number of notches and it must work faster to cover the same amount of distance)

Rotational velocity deals with whether or not the two objects are connected with an axel.
Rotational velocity deals a lot with train wheels.

Train wheels "self-correct".  1) train wheels have the same rotational velocity because they are connected 2) The wheels are tapered so the thicker part of the wheel has a higher tangential velocity (meaning it is covering more distance per time than the thinner part). 3)The thicker side thus moves faster(linear velocity). 4) So the wheel on that side will curve inward and push the axel to the opposite side (self correct).

A carousel has the same rotational velocity since you are riding on the same wheel as the other
person


Rotational inertia is a little different than rotational velocity. Rotational inertia is an object's willingness to speed up or slow down as it is rotating. If you have more rotational inertia your velocity is slower. If you have less rotational inertia, your velocity is faster.

So if I were spinning on ice, and I had my arms farther away from my body, then I would spinning slower. If I pulled my arms in, I would spin faster. When my arms are out, my mass is more distributed and farther away from my rotational axis. I will have more rotational inertia and therefore my velocity is slower. When my arms are in I have less rotational inertia because more mass is closer to my rotational axis and therefore my velocity is faster.

This concept deals a lot with Angular Momentum and conserving it.
Angular momentum= rotational inertia x rotational velocity.
When my arms are spread, my rotational inertia is larger and my rotational velocity is smaller. (in the equation)
put an = sign in the middle to show that when I put my arms in, the equation is equal. On the other side of the equation its the rotational inertia that is smaller and my rotational velocity that is larger.



Lets talk about torques.
Torques cause rotation.
There are two things about torques: they must have a force and they must be perpendicular.
If you need a larger torque, you must increase the lever arm, increase the force, or both.

A long lever arm takes less force, and a small lever arm needs more force. So If you have a really tight bolt, you will want to use something longer to loosen it.
hint* in a system= torques must always be equal to balance. (however the forces or weight does not)

Remember the equation: Counterclockwise torque= clockwise torque

                                        Force x lever arm   =   Force x lever arm

                                        (plug stuff in)

               *don't forget to show math, and don't forget to have the units of measurement



If the object on the scale has N, then you already have the weight and you do not need to work to find it before using the torque equation.

If you cut a bat in half at the center of gravity: Will the thicker side weigh more?
Remember that a shorter lever arm will have a bigger force (weight) so whichever side has a shorter lever arm will weigh more.



Lets talk about your center of gravity:
Its the middle of the distribution of your mass.
You want your center of gravity to stay within your base of support: which is how far apart your feet are spread. If your center of gravity comes out of your base of support, then you will fall over, or you will be easier to push over.

Now we can talk about centripetal and centrifugal forces.
The answer to a problem will never be:
centrifulgal force
its not centrifulgal force
or anything dealing with centrifugal force because its not real.

Centripetal force is the inward force that pulls on an object that is rotating, or rounding a curve.
The force that pushes you sideways when the car rounds a corner doesn't exist. Its merely newton's 1st law- you just want to keep moving in the direction the car was previously moving.
If there is someone next to you and you think that you hit them, you didn't. They actually hit you.


That's all for Unit  4!

I really enjoyed this unit and had fun learning about it. I learned a lot and it made sense to me. Hopefully I will do well on the test!

torque

This movie is a metaphor for torques. If you watch it, you can draw the parallel from the meaning of the movie and how it applies to the definition of a torque. The movie's whole point is that you live in a world that is constantly moving or rotating, just like the idea of torques. Like the wheels on the bikes that the actors are riding, torques cause rotation.

Meter Stick

Trying to find the mass of a meter stick without using a scale has thus far proven to be quite a challenge. I know that the point is to find the lever arm of the other side of the meter stick, but I have not figured out how yet. Lauren and I took some measurements and did some calculations. One thing we did clarify is that the center of gravity is supposed to be at 50cm. So we werent sure how to approach the problem, however we knew that f=mxg... and if we could calculate g and therefore f.. then we can solve for the mass. Also an important thing that we needed to know was that the center of gravity was at 50cm and that both lever arms therefore were 25cm roughly.


Here are the steps that we came up with:

Use torque equation
Find the lever arm of the weight side
find torque
Torques must be equal
set equation equal to eachother
solve for force
force is weight
w=mg
solve for mass
you done :)

tip*  force x lever arm = force x lever arm
  

This video explains the laws of angular momentum and what it means. The guy explains that angular momentum is the inertia of rotation of a rotating or spinning object . We can think of wheels, or planets, or anything rotating around another object.

Angular momentum deals with direction and magnitude.