Which of these examples primarily involves torque:

1."A crowbar used to move a heavy object.",

2."A bullet shot from a rifle.",

3."A ball bouncing off a floor.

Reading Quiz

Revolutions, degrees, or radians are different units for describing the rotational displacement

of the merry-go-round.

There is a close resemblance between quantities used to describe linear motion and those

used to describe rotational motion.

Lecture Quiz - Question 1:

“How many radians are there in one complete revolution?

1. Zero (0)

2. One (1)

3. Pi ()

4. 2 Pi (2

5.

Lecture Quiz - Question 2:

What is the angular speed of the second hand of a clock, in radians per second:

1. rad/sec

2. rad/sec

. rad/sec

4. rad/sec

5. rad/sec

A single concentrated mass at the end of a very light rod is set into rotation by the applied force F. Use Newton’s second law to find the acceleration.

Figure 8.19The gravitational force acting on the planet

produces no torque about an axis through the sun because the lever arm is zero for this force.

How far can the child walk without tipping the plank? The entire weight of the plank can be treated as

though it is located at the center of gravity.

Lecture Quiz

4. Assume the length of the board is 3 meters, and 1 meter hangs over the edge. The board has a mass of 9 kg, and the child’s mass is 21 kg. If you ignore the boy, what is the torque about the pivot point due to the board?

1. 0 N.m 2. 4.5 N.m

3. 9 N.m 4. 90 N.m

5. 45 N.m

Lecture Quiz 16

5. Assume the length of the board is 3 meters, and 1 meter hangs over the edge. The board has a mass of 9 kg, and the child’s mass is 21 kg. If the boy stands at the end of the board, how much torque does he exert on the pivot point?

1. 0 N.m 2. 21 N.m

3. 31.5 N.m 4. 210 N.m

5. 630 N.m

Lecture Quiz 16

6. Assume the length of the board is 3 meters, and 1 meter hangs over the edge. The board has a mass of 9 kg, and the child’s mass is 21 kg. About how far out can the boy go without the board tipping?

1. 0 cm 2. 10 cm

3. 20 cm 4. 43 cm

5. 60 cm

(Choose the closest answer.)

Rotational Inertia

The resistance to change in rotational motion.

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τ =Iω

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I = mr2

= Mass x distance from axis squared

Figure 8.15Expressions for the rotational inertia of

several objects, each with a uniform distribution of mass over its volume. The letter m is used to

represent the total mass of the object.