Unit 4 Summer Blog Post
In this unit we learned a lot about rotational and tangential velocity, Rotational Inertia and Angular Momentum, Torque, and centripetal force.
Rotational and
Tangential Velocity
Tangential Speed- this is the speed of an object moving in
along circular path. (radial distance x rotational spin) or (v~rw)
Rotational Speed- (A.K.A angular speed) involves the amount
of rotations per unit of time.
In the photograph above we see two little girls on a
carousel. A carousel is the perfect demonstration to compare tangential and
rotational speed. In this picture, you will recognize that these girls are
going to rotate the same number of times.
However, the little nugget on the
left has a greater tangential velocity. This is because she is located further
from the axis of rotation and will have to cover the same amount of distance
than the girl on the right in the same amount of time.
How are train wheel designed to
keep them on the track?
Train wheels are designed tapered with the fat/ wider part
in the middle and the more narrow part on the outside. 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 in the middle
causes the train to always move towards the middle of the track.
This is probably wordy and might make no sense, so for more
information watch this video we made!
Rotational Inertia
and Angular Momentum
In previous blog posts, we have discussed inertia, which is
the property of an object to resist changes in motion.
However, Rotational Inertia is the property of an object to
resist the spin.
In rotational inertia it is important to notice mass
distribution. Where the mass is located has a huge affect on the speed.
In the image above, you can see that the ice skater with her
mass distributed closer to her body, increases her speed.
We know that angular momentum
before=angular momentum after.
When she is in a tight ball, her mass is closer to her axis
of rotation. When she spreads out, her mass is farther from the axis. In the
ball she has a very fast ROTATIONAL VELOCITY and a small rotational inertia.
But the one with her arms out has a small rotational velocity and a big
ROTATIONAL INERTIA. Thus, ROTATIONAL VELOCITY x rotational inertia= rotational
velocity x ROTATIONAL INERTIA. Because
her arms are closer to her body, her momentum is conserved, when she extends
her body and moves her mass further from the axis of rotation, it increases her
rotational inertia but her rotational velocity will decrease.
Torque
Torque causes something to rotate.
Torque= (Force) (lever arm)
A lever arm is the distance away from the axis of rotation.
Below are pictures of wrenches. The longest one or the one
with the bigger lever arm will have more torque.
Now, because torque causes rotation, how do we stay
balanced?
For starts, our torque has to stay balanced. We must have
equal torques.
Another concept that is important in understanding torque is
the center of mass (an objects average position of mass). You also have a base
of support. If the center of mass is with in the base of support, it will not
tip over. This is one of the reasons football players bend their legs apart
(bigger base of support) and bend their knees (lower center of gravity).
- w=mg
- Torque= F x lever arm
F x lever arm = F x lever arm.
1 (2) = 2(F)
2= 2F
1=F
1N
This is an example equation of solving for the weight of a side of the meter stick.
Centripetal Force
A centripetal force is a center seeking force. It keeps you going on a curve. You can find the centripetal force by adding the Fweight and Fsupport. A centrifugal force is a center fleeing force that doesn’t exist.
Why do clothes get drier in the spin cycle of the washing machine? Because the centripetal force of the wall keeps the clothes in while it moves at a certain velocity that keeps the clothes spinning. This is also the reason the cup stays in its curved path.
Thank you for reading!
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