1. Rotational & Circular Motion
Sara Sultan
24/04/2019

2. Rotation of rigid objects around fixed axis
The variables that are used to describe this type of motion are similar to those we use to describe linear motion: Angular position, Angular velocity, Angular acceleration.
24/04/2019

3. When a rigid body rotates about a fixed axis, the angular displacements is the angle, swept out by a line passing through any point on the body and intersecting the axis of rotation perpendicularly.
24/04/2019

4. d2 d1
The ants moved different
distances: d1 is less than d2

5. Angle is a simpler quantity than distance
Both ants moved the
Same angle: q1 = q2 (=q)
Angle is a simpler quantity than distance
for describing rotational motion

6. Angular Position

7. (in radians)
For 1 full rotation,

8. Arc Length

9. Angular Displacement

10. Degree (1 full turn 3600 degree) Revolution (rev) RPM
Angular displacement is expressed in one of three units:
Degree (1 full turn 3600 degree)
Revolution (rev) RPM
Radian (rad) SI unit

11. Angular Speed and Velocity

12. Angular Speed is a Vector!
Works for angular acceleration as well.
We use a “right hand rule” to determine the vector direction of a rotation. Using your right hand, curl your fingers in the direction of the rotation. Your thumb points in the direction of the rotation.

13. Angular Acceleration

14. Summary of angular motions.
Angular position, radians, measure counter-clockwise.
Angular velocity, radians per second.
Angular acceleration, radians per second squared.
Note that radians are a dimensionless quantity.
Radians = Degrees * p/180
Example: 180 degrees = 3.14 radians

15. Moment of inertia M M I  Mr2 r r I=small I=large (same M)x
I  Mr2 r r
r = dist from axis of rotation
I=small
I=large
(same M)
easy to turn
harder to turn

16. 24/04/2019