Removing electrons from an atom (or a material) means that there are more positively-charged protons and fewer negatively-charged electrons. So the atom or material has an overall positive charge, and this is why the jersey we mentioned above sticks to your body or your hair. The charge either attracts and pulls things towards the object, or repels and pushes things away from the object. In the example of the balloon, the balloon was attracted to the wall. Positive and negative charges, which are unlike, attract each other. If two objects have the same charge, they repel each other.
Shocks or sparks and static electricity
Have you ever felt an electric shock when touching a metal door handle? The shock is caused by static electricity.
If you walk across a nylon or wool carpet, electrons will move from the carpet onto you. You have gained electrons and you have a negative charge. If you touch a metal door handle, which conducts electrons, then the electrons move from you to the door handle. You will feel a static shock. If it is dark you will see a spark of static electricity. Usually you will only notice static electricity when the air is very dry. When the air is more humid, water in the air helps electrons move off your body quickly so that no charges build up on your body.
Practical activity 1 Group work
AIM To see how rubbing certain objects together leads to forces of attraction or repulsion.
HYPOTHESIS Friction causes objects to become electrically charged.
METHOD Step 1 Hold the ruler in one hand and rub it for a few minutes with the cloth.
Step 2 Bring the ruler close to the pieces of tissue paper or sawdust.
RESULTS 1 Record what you observed. 2 Explain your observations in terms of same or opposite charges on the materials.
3 Describe other situations similar to this that you have experienced.
CONCLUSION Objects that have no effect on each other otherwise stick together or repel each other after being rubbed together. This shows that friction causes objects to become electrically charged.
Investigate static electricity
MATERIALS • a plastic or perspex ruler
• a dry silk or wool cloth
• small pieces of tissue paper or sawdust
The atoms of the dry cloth become negatively charged as they gain electrons.
– – – – – –
– – – – – –
The atoms of the ruler become positively charged as they lose electrons.
Figure 2 Charging by friction
Unit 1 Friction and static electricity 105
New words
attract – pull towards repel – push away
STRAND 3
+ + + + + + + + + + + + + +
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