Chapter 8 - Rotational Motion of Solid Objects

Question 1

What is a rotational motion?

Answer 1

• Rotational motion involves an object rotating about an axis
  e.g. yoyo
• Its how fast the object is turning

Question 2

How much is one revolution?

Answer 2

2π (rad/s^2)

Question 3

What is torque?

Answer 3

The product of the force and the distance from the fulcrum(pivot) is called the torque

Question 4

Torques that produce counter clockwise rotation are?

Answer 4

positive

Question 5

Torques that produce clockwise rotation are?

Answer 5

negative

Question 6

Where is the centre of gravity of an object?

Answer 6

The point about which the weight of the object itself exerts no torque

Question 7

What determines the acceleration for rotational forces?

Answer 7

torque and moment inertia

Question 8

What is moment inertia (rotational inertia)?

Answer 8

• The resistance of an object to change in its rotational motion
• Rotational inertia is related to the mass of the object
• It also depends on how the mass is distributed about the axis of rotation

Question 9

What does the resistance to a change in rotational motion depend on?

Answer 9

• The mass of the object
• The square of the distance of the mass from the axis of rotation

Question 10

What is the equation for an object with its mass concentrated at a point?

Answer 10

• Rotational inertia = mass x square of distance from axis
• I = mr^2

Question 11

What is Newton’s second law for rotational motion?

Answer 11

• The net torque acting on an object about a given axis is equal to the rotational inertia of the object about that axis times the rotational acceleration of the object.
• The rotational acceleration produced is equal to the torque divided by the rotational inertia

Question 12

What is angular momentum?

Answer 12

Angular momentum(rotational momentum) is rotational inertia times rotational velocity
L = Iω

Question 13

How is Angular momentum conserved?

Answer 13

Angular momentum is conserved by changing the angular velocity

Question 14

What is Kepler’s second law?

Answer 14

• Kepler’s second law says that the radius line from the sun to the planet sweeps out equal areas in equal times
• The planet moves faster in its elliptical orbit when it is nearer to the sun than when it is farther from the sun
• This is due to conservation of angular momentum

Question 15

Is Angular momentum a scalar or vector?

Answer 15

• Angular momentum is a vector
• The direction of the rotational-velocity vector is given by the right-hand rule
• The direction of the angular-momentum vector is the same as the rotational velocity