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