Unit 4 Blog Reflection

I. Rotational and Tangential Velocities

II. Rotational Inertia/Conservation of Angular Momentum

III. Torque

IV. Center of Mass/Gravity

V. Centripetal/Centrifugal Force

I. Rotational Velocity: Number of times you rotate per unit of time (Angular Speed)
   Tangential Velocity: The speed of something moving around a circular path
   Linear Velocity: The same as Tangential Speed


Less rotational inertia=easier to spin

This Unit told us that the center of a rotating circle moves slower than the outer parts of that circle. This is because they are rotation with the same rotational velocity, however, once you look on the outside which is much larger than the inside, you have to wander how it stays balanced or keeps up with the inside. It has more ground to cover therefore it goes faster.





II. Rotational Inertia: It is the property of an object to resist changes in spin
Lots of rotational inertia = harder to spin
A little rotational Inertia = easier to spin




Who is spinning faster, the one at the left or the one at the right?
Well the one on the left is because she is decreasing her rotational inertia by bringing her arms in which makes her rotate much faster than the one on the left who has her arms out.

Conservation of angular momentum means:
total momentum before = same momentum after
R.I. x R.V. before = R.I. x R.V. after
So if I have a.... R.I. x r.v. = r.i. x R.V.
angular momentum = rotational inertia x rotational velocity

III. Torque: something that causes rotation
      Torque = Force x Lever arm ( where the lever arm is the distance from the axis of rotation)
The bigger the lever arm the less force it takes to put into an object

IV. Center of Mass: the average position of an objects mass
      Center of Gravity: when gravity acts on the center of mass
This is why in football we bend our legs because one, we lower our center of gravity which makes it harder for us to fall over and two other players are bending their legs, but whoever gets their center of gravity the lowest, they will run over their opponents.


 
V. Centripetal/Centrifugal Force
     Centripetal force is the force that helps us turn. It does this by pulling us inward while we are wanting to go outward.





This unit seemed to be very interesting to me. Although I did reach my goal of understanding the material alot  better and actually paying attention in class, I feel that I need to do that alot often. As seen in the torque lab, I found the meter stick problem really challenging, however after constantly practicing it, I feel that I have mastered that concept. Physics is seen in everyday life, and more specifically, rotation is seen in everyday life, so this helped me understand something from real life.

The Meter Stick Lab

Our goal for the meter stick lab was to find the weight of the meter stick without weighing it, but instead using a table, an 100g weight, and the meter stick itself. The formulas that we will need to use in order to solve this problem are: w = m*g
                    lever arm * F = lever arm * F (counter-clockwise torque = clockwise torque)



To start this project, we had to find the center point of the meter stick as it balances on the table. Luckily, it balanced directly at the halfway mark which was 50 cm. Next you must add the 100g weight to the end of the meter stick, and immediately, we see that the meter stick drops off the table. Why is this? It's simply because it isn't balanced. In order for it to balance out, you would have to slide the meter stick creating what we scientifically would call a lever arm in order to find the torque of the object.





This is an example of what the new lab would look like. Seeing this, we can add the formula for torque which is: Lever Arm 1= 30         Lever Arm 2 = 20
counter-clockwise torque = clockwise torque
(lever arm)(F) = (lever arm)(F)
(30)(.98) = (20)(F)
29.4 = (20)(F)
  20         20
1.47N = F

W = (M)(G)
1.47N = (M)(9.8)
  9.8           9.8
.15Kg = M
150g = M

(Actual mass was 150.8)

Torque and Center of Gravity

This video is a great video because it makes it hands on.

Rotational Inertia

I chose this video because it shows us through a hands on demonstration the way that Rotational Inertia works. This video is short, sweet, and gets to the point.