Rotational Motion and Torque

Chapter 7 and 8

Physics

- When an object spins it is said to undergo rotational motion. (motion of a body as it spins around an axis of rotation)

- Rotational motion is described in terms of the angle through which a point moves around the circle.

- Angles measured in radians

360o = 2 radians ------- 1 radian is

approximately 57o

1 radian = 57.2957 degrees

1 degree = 0.0174532 radians

- Angular displacement -the angle through which a point, line, or body is rotated in a specific direction and around a specific axis

- Angular speed (ω)– the rate at which a body rotates about an axis (radians per second)

• Torque – a quantity that measures the ability of a force to rotate an object around some axis

• Lever arm – perpendicular distance from the axis of rotation to a line drawn along the direction of force

Torque = force x lever arm x angle of rotation

= F•d•(sinθ)

= torque

F = force

d = distance from applied force to axis of rotation

θ = angle of rotation

Example – Trying to open a door by pushing or pulling at the handle vs. trying to open the door by pushing or pulling beside the hinge. Which is harder?

** More torque is produced with a longer lever arm.** When doing work, you want to maximize torque

by making the lever arm as long as possible, thus making the rotation easier. Long wrench vs. short wrench.

- Torque will be positive or negative based on the direction of rotation

Yea, Homework!

Chapter 7 - Review problems

Pages 269-273

#1, 2, 3, 4, 26, 27, 29, 30, 31, 32, 33

Chapter 8 – Review problems

Pages 305-309

#1, 2, 3, 7, 8, 12