physics - static electricity + magnetism

Why do things become negatively or positively charged when they are rubbed

Because of friction when two different materials are rubbed together electrons can be transferred from one material to another, the material that gains electrons becomes negatively charged and the material that loses electrons becomes positively charged.

Why do hairs stand on end when touching a Van de Graff generator

The generator transfers charge onto the person and each strand of hair picks up the same charge. Like charges repel - so the hairs repel from each other and stand up

Why is a spark seen when a conducting sphere is placed nearby to a Van de graff conductor

The Van de Graaff builds up charge. When a metal sphere gets close, the charge jumps through the air as a spark.This happens because the air briefly becomes a conductor.

What is a situation where electrostatics are useful? Why is this?

Painting cars with spray paint - the paint is given a positive charge and the car is given a negative charge so the paint is attracted to the car and sticks to it

What is a situation where electro statics are dangerous and why? What can be done to stop this?

Fuelling cars or planes - when doing this the fuel can build up a static charge and if the charge gets big enough it can cause a spark which could catch fire. If the vehicle is earthed it means the earth can absorb and extra static charge safely.

How would you draw an electric field around a positive charge?

A circle with arrow pointing out

How would you draw an electric field around a negative charge

A circle with arrows pointing in

Define magnetic field

The area around a magnet where magnetic forces act