2. Do now: The propeller blades of an aircraft rotate with a frequency of 40Hz. If the blades have a radius of 85cm how fast do the tips of the propeller blades move? Paraire, 11 Mahuru 2015 Homework reminder: Set 1 and 2 should now be finished This week: work on Set 3 (forces and circles) and Set 4 (gravitation and satellites)

3. Recall: period (T) - time it takes to make one full rotation (revolution, cycle), measured in s Frequency (f) – number of rotations per second (Hz or s -1 ) Distance travelled in one rotation is the circumference: Speed of an object moving in a circle of radius r is:

4. During a hammer throw, a steel ball is swung horizontally with a constant speed of 10ms -1 in a circle of radius 2.0m. 1)Calculate the frequency of rotation 2)Sketch a vector diagram to show the change in velocity as the steel ball moves from point P to point Q P Q 10ms -1 2.0m

5. To keep an object moving in a circular motion, a force must act to push it toward the centre of the circle. a This force is called a centripetal force. F F C keeps the ball on a circular orbit - otherwise it flies off at a tangent.

6. Circular Motion Centripetal force and acceleration can be calculated using the following formulae: v=speed(ms -1 ) r=radius of motion

7. During a hammer throw, a steel ball is swung horizontally with a constant speed of 10ms -1 in a circle of radius 2.0m. The steel ball has a mass of 7.0kg 3)Calculate the force required to keep the ball moving in a circle P Q 10ms -1 2.0m

8. 1)Centripetal force is not magic. It must come from somewhere. Explain what supplies the centripetal force for each of these circular motions: a)The earth around the sun b)An electron around a proton c)A car travelling around a corner d)A stone being swung on the end of a string 2)A car travels around a corner. Why does loose change on the dashboard slide around? 3)Explain what happens in circular motion if the centripetal force is removed.