Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Collisions with electrostatic forces

Demonstration

An illustration of a collision with 'invisible' forces.

Apparatus and materials

Ping-pong ball coated with Aquadag, 2

Van de Graaff generator

Fine nylon suspension

Health & Safety and Technical


Do not add extra capacitance to the Van de Graaff generator. 

Van de Graaff generator safey

Coat the two ping-pong balls with Aquadag to make their surfaces conduct. Using the fine nylon thread, suspend them one diameter apart, preferably from the ceiling but in any case on threads as long as possible.

 

Procedure


Van de Graff generator

a Switch on the Van de Graaff generator and charge each of the balls by allowing them successively to touch its sphere. 
 
b Study collision processes between the charged balls by drawing back one of the threads and allowing the balls to swing together. The 90° angle between paths after collision may be seen. 
 
c You could also demonstrate collisions of the charged ping-pong ball with the Van de Graaff sphere.


Teaching notes


Step c provides a useful introduction on the scattering of alpha particles in gold foil. 

 

Related notes


Van de Graaff generator - the basics