U5: Forces

Key Learning Points:

In this chapter you've learnt about the 4 types of forces.

(a) Frictional Forces (Or Friction)

• This force exists whenever 2 surfaces come into contact with each other
• Friction opposes (resist) motion and can cause wear and tear as well as producing heat (thereby causing overheating in machinery)
• However without it, we will not be able to walk properly or hold onto things
• We can never eliminate friction but we can reduce them
• Methods include adding lubricants (oil or grease), rollers and wheels, ball bearings or powder

(b) Gravitational Forces (Or Gravity)

• This is the pulling force of the Earth on all objects, which is measure by our weight
• It is different from mass, which is how much matter an object has
• Thus weight is NOT EQUAL to mass
• Gravity can work against us (e.g. climbing up stairs require more force to overcome gravity) or work in our favour (e.g. going down a slope)
• The gravity on the moon is 1/6 of the Earth's gravity. Thus we would weigh lighter on the moon than on the Earth

(c) Elastic Spring Force

• This force is present in springs or elastic bands
• When a pulling force is applied, the spring or elastic band is stretched. Upon releasing, the elastic spring force will cause the spring or elastic band to return to its original length
• The original length of the spring will be when there is no force/mass attached to it
• The extension of the spring is the result of a pulling force exerted on it

(d) Magnetic Force

• These are the forces of attraction and repulsion of a magnet
• Like poles of a magnet repels (pushes away) while unlike poles attract (pulls together)
• Magnetic materials can be attracted to a magnet, regardless of the poles
• E.g. Steel, Iron, Nickel, Cobalt, Manganese
• Magnetic material are not magnets. They need to be magnetised first either by the stroking method or the electrical method (resulting in an electromagnet)