forces and pressure

1. frictional force (friction)

1.1. friction a force produced by 2 moving surfaces in contact. it opposes and slows down movement

1.2. friction is useful in everyday life. for example, it is needed for walking

1.3. friction can be a nuisance. ways to reduce friction include using smooth surfaces, ball bearings, lubricants, and by streaming

2. effects of forces

2.1. change the shape or size of an object

2.2. start an object moving or stop a moving object

2.3. speed up or slow down a moving object

3. what is pressure?

3.1. pressure is the force extered per unit area

3.2. pressure increases when force increases or area decreases

3.3. pressure decreases when force decreases or area increases

4. gravitational force

4.1. the force of gravity is a force that pulls objects towards the centre of the earth

4.2. the force of gravity pulling down on an object is called weight

5. magnetic force

5.1. friction is the force of attraction produced by magnets on objects made of iron of steel

5.2. magnets can also attract or repel other magnets