9.2 Physics Review
If a trapeze artist rotates twice each second while sailing through the air, and contracts to reduce her rotational inertia to one-third, how many rotations per second will result?
6 rotations per second
Which will have the greater acceleration rolling down an incline: a bowling ball or a volleyball? Why?
Bowling ball: less rotational inertia per mass so the larger overall mass does not matter
What happens to a gymnast's angular momentum when he changes his body configuration during a somersault? What happens to his rotational speed?
angular momentum is unchanged; rotational speed is either increased or decreased
How can a person vary his or her rotational velocity and rotational speed?
by varying his or her body configuration
If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her rate of spin increase?
doubled
When is angular momentum conserved?
when there is no external torque
The most popular gyroscope around is a Frisbee flying disk. What is one function of its somewhat thicker curved rim?
Increases rotational inertia and stability
Considering the three axes of rotation within the human body, give an example of a movement that would rotate each axis.
Longitudinal is rotated during a standing spin. Median is rotated during a cartwheel. Transverse is rotated during a flip.
Consider two rotating bicycle wheels, one filled with air and the other filled with water. Which would be more difficult to stop rotating? Explain.
One filled with water because it has a greater rotational inertia
If you walked along the top of a fence why would holding your arms out help you to balance?
increases your rotational inertia
What is the effect of adding a weight to the end of a baseball bat used for practice swings?
it adds to your rotational inertia, which make a regular bat easier to swing later
Why is it easier to swing your legs back and forth when they are bent?
less rotational inertia
Distinguish between linear momentum and angular momentum.
linear momentum is along a straight line path and angular momentum always involves rotation
Considering the three axes of rotation within the human body, Which axis has the least rotational inertia? Why?
longitudinal axis because mass is concentrated closer to the axis resulting in a smaller radius
On what two quantities does rotational inertia depend?
mass and radial distance from the axis
What is the law of inertia for rotation?
rotating objects tend to remain rotating
Which will have a greater acceleration rolling down an incline, a large ball or a small ball?
same: both have the same rotational inertia per mass
Which will have a greater acceleration rolling down an incline, a hoop or a solid disk?
solid disk: less rotational inertia per mass
What does it mean to say that angular momentum is conserved?
total or net momentum does not change from before to after an event
