Procedure Place string through the tube and tie one end to the bob and the other to the Newton weights.
Swing the bob in a horizontal plane. Vary the speed of the bob and note how the radius of rotation changes.
Repeat the process with different tension (centripetal force) by varying the number of Newton weights.
Observation
The faster the bob travels, the greater the radius of rotation for a given centripetal force.
Conclusion The relationship between force and velocity and radius is demonstrated.
Note
If measurements of mass of bob (m), radius or rotation (r ), periodic time for revolution (T) and force due to the Newton weight (F) are all taken, then the equation F m2r can be shown to be true, where
v 2p T
. Newton weights Fig 6.3 Tube String Pendulum bob
SAMPLE PROBLEM 6C
What is the tension on the wire of a hammer when the thrower is spinning, given that the ball, of mass 7.25 kg, is travelling at 28 m s1 and the radius of its motion is 2 m?
SAMPLE ANSWER 6C Using the formula for centripetal force, making sure all values are in their standard unit:
