Physics Chapter 9,10,11 Review

On what two quantities does rotational inertia depend?

Mass and distribution of mass.

A ladybug in the bottom of a whirling tin can feels a centrifugal force pushing it against the bottom of the can. Is there an outside source of this force? Can you identify this as the action force of an action-reaction pair? If so, what is the reaction force?

No. No. There is no reaction force.

Why is the CG of a baseball bat not at its midpoint?

There is more mass at the end of the bat

When is angular momentum conserved?

When no net external torque acts on a system.

From the equations F=mv2 ,calculate the tension in a 2-m length of string that whirls a 1-kg mass at 2 m/s in a horizontal circle

2 N

If the string that holds a whirling can in its circular path breaks, what causes the can to move in a straight-line path - centripetal force, centrifugal force oar a lack of force? What law of physics supports your answer?

A lack of force. This is an example of Newton's 1st Law - the law of inertia.

Compare the effects of a force and a torque exerted on an object.

A net force causes linear acceleration and a net torque causes rotational acceleration.

Does an inward force or an outward force act on the clothes during the spin cycle of an automatic washer?

An inward force.

How far can an object be tipped before it topples over?

An object can be tipped until the CG is outside the base of support.

What is the law of inertia for rotation?

An object that is rotating will continue to rotate unless acted upon by a net torque. Rotating objects tend to remain the same.

Cite an example of an object that has a CG where no physical material exists.

Any object that is hollow, curved or angular. Some examples would be donuts, a boomerang, and a hollow ball

At a given rotational speed, how does linear (or tangential) speed change as the distance from the axis changes?

As the distance from the axis increases, the linear speed increases. The relationship is directly proportional.

At a given distance from the axis, how does linear (or tangential) speed change as rotational speed changes?

As the rotational speed increases, the linear speed increases. The relationship is directly proportional.

How can a person vary his or her rotational velocity and rotational speed?

By changing the shape of his or her body.

Why do you spread your feet farther apart when standing in a bumpy-riding bus?

By spreading your feet you increase the width of your base this increases you stability.

Why can you not successfully bend over and touch your toes when you stand with your heels against the wall?

By standing against the wall you cannot change your CG. This causes you to topple forward. (CG will extend beyond your support base and you will topple)

How can the CG of an irregularly shaped object be determined?

CG can be determined by suspending the object and marking the plumb line. Repeat for two or three more points to find CG. (By suspending it from two or more points and see where the lines of suspension intersect)

When a car makes a turn, do seat belts provide you with a centripetal force or a centrifugal force?

Centripetal force.

Why is the centrifugal force the ladybug feels in the rotating frame called a fictitious force?

It is a result of rotation. It is not part of an interaction between two objects.

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?

It will double.

What is the lever arm of a force?

It's the perpendicular distance from line of force to the axis of rotation.

Why does the Leaning Tower of Pisa not topple?

Its CG is above the support base (CG = Center of gravity)

Distinguish between linear momentum and angular momentum.

Linear momentum is the inertia of motion and angular momentum is the inertia of rotation

Distinguish between linear speed and rotational speed.

Linear speed is distance covered per time. Rotational speed is the number of rotations per time.

In what direction should a force be applied to produce maximum torque?

Perpendicular

Distinguish between a rotation and a revolution.

Rotation is when and object turns about an internal axis. Revolution is when an object turns about an external axis.

What is linear speed called when something moves in a circle?

Tangential speed

Identify the action and reaction forces in the interaction between the ladybug and the whirling can in Figure 9.10.

The can pushes the ladybug inward. The ladybug pushes the can outward. (Bug on can, Can on Bug)

What part of an object follows a smooth path when the object is made to spin through the air or across a flat smooth surface?

The center of gravity follows the smooth path

Does a child on a merry-go-round revolve or rotate around the merry-go-round's axis?

The child revolves around the merry-go-round's axis.

When you whirl a can at the end of a string in a circular path, what is the direction of the force that acts on the can?

The force is toward the center of the circle.

When you roll a cylinder across a surface it follows a straight-line path. A tapered cup rolled on the same surface follows a circular path. Why?

The smaller end of the cup travels less distance in one revolution than the large end of the cup. This results in a curved path for the cup.

Which will have the greater acceleration rolling down an incline - a hoop or a solid disk?

The solid disk would have a greater acceleration. Less rotational inertia per mass

Which will have the greater acceleration rolling down an incline - a large ball or a small ball?

They would have the same acceleration.

Does the force that holds the riders on the carnival ride in Figure 9.1 act toward or away from the center?

Toward the center.

What does it mean to say that angular momentum is conserved?

Unless a net torque acts on a rotating system, the angular momentum of an object is constant. It doesn't change after some event.