Chapter 8

A baseball bat can be rotated around many different axes of rotation. Three such possibilities are shown in (Figure 1). Rank the baseball bat's moment of inertia about each of these three axes of rotation. Rank the moment of inertia from largest to smallest and overlap axes labels if the same.

B_A_C

Given the same baseball bat and possible axes of rotation shown in (Figure 1), for which axis of rotation would it be the easiest to rotate the bat from rest?

C

Rate the rotational inertias about each axis from large to small. Rank rotational inertias from largest to smallest. To rank items as equivalent, overlap them.

Ic-Ib-Ia

Is it easier for a circus performer to balance a long rod held vertically with people hanging off the other end, or the same long rod without the people at the other end, and why? View Available Hint(s)for Part D Hint 1for Part D. Mass distribution, rotational inertia, and tendency to tip over (rotate)

It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is greater. Submit

Is it easier to balance a long rod with a mass attached to it when the mass is closer to your hand or when the mass is farther away? View Available Hint(s)for Part A Hint 1for Part A. Review a specific part of the video.

It is easier when the mass is farther from your hand.

A girl spins around in a circle trying to make herself dizzy. Without changing her position, she starts spinning twice as fast. By how much did her rotational kinetic energy change?

It quadrupled.

Inertia depends on mass. Does rotational inertia depend on mass also?

Rotational inertia depends on the distribution of mass about the axis of rotation.

Why does the rotational inertia of the rod with the attached mass closer to your hand compare the way it does with the rotational inertial of the rod with the attached mass farther away? View Available Hint(s)for Part C Hint 1for Part C. Rotational inertia and mass distribution

Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The farther the mass is, the higher the rotational inertia.

How is rotational inertia similar to inertia as studied in previous chapters?

Rotational inertia is the resistance to a change in rotational motion, which is similar to inertia which is a resistance to a change in velocity.

What kind of force acts on a ladybug inside a can that is whirled in a circular path?

The can exerts on the ladybug an inward centripetal force.

How does the rotational inertia of the rod with the mass toward the bottom compare with the rotational inertia of the mass toward the top? View Available Hint(s)for Part B Hint 1for Part B. Rotational inertia and balance point

The rotational inertia of the rod with the mass closer to the top is greater than the rotational inertia of the rod with the mass closer to the bottom.

Do seat belts provide a centripetal or centrifugal force on a passenger in a car rounding a curve?

The seat belts provide a centripetal force on the passenger.

How does the tapered rim of a wheel on a railroad train rolling along a track allow one part of the rim to roll faster than another part?

The tangential speed is proportional to the radius. The inside of the wheel rolls on a larger radius than the outside of the wheel.

Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of a washing machine?

The tub of the machine exerts centripetal inward force on clothes.

When you whirl a can overhead by a string in a circular path, what is the direction of the force exerted on the can?

Toward the center of the circle.

Rank them in reaching the bottom: winner, second place, and third place. Drag the appropriate items to their respective bins.

Winner B_ Second place A_ Third Place C_

Does this mean the tangential speed of the wide-end rim differs with that of the narrow-end rim?

Yes, the tangential speed of the wide end is faster.

The center of gravity of a basketball is located _______. View Available Hint(s)for Part A Hint 1for Part A. How is center of gravity defined?

at its geometrical center

The tangential speed on the outer edge of a rotating carousel is _______. View Available Hint(s)for Part A Hint 1for Part A. Distinguish between linear and rotational speed.

greater than toward the center

Rotational inertia of an object rotating about an axis becomes greater with _______. View Available Hint(s)for Part A Hint 1for Part A. Consider the rotational inertias of objects discussed in Section 8.4 in the textbook.

increased mass and increased distance to mass concentration

The rotational speed of every point of a rotating rigid object _______. View Available Hint(s)for Part A Hint 1for Part A. What is rotational speed?

is the same

To improve the performance of a racing bicycle, the mass of the tires and rims is reduced so there is ____________.

less rotational inertia

What are the units of measurement for tangential speed and rotational speed?

m/sm/s for tangential, rpmrpm for rotational

A solid sphere and a hollow sphere (spherical shell) of the same mass and same radius rotate with the same amount of kinetic energy. Which one is rotating faster?

the solid sphere