If you kick a ball across a playground, it bounces and
rolls on the ground’s rough surface and soon comes to a halt. What slows
it down is friction, which is the force between a moving object and whatever it
touches. Cars travel faster if they are STREAMLINED to reduce a
type of friction called air resistance. Friction can sometimes be helpful.
Without friction between the tyres and the road, cars would not have enough
grip to go around corners.
Slippery substances such as oil reduce the friction between two
surfaces. This is known as lubrication. Machinery has to be lubricated to
prevent its moving parts from wearing out due to friction. Most machines are
oiled or greased when they are made and are lubricated from time to time as
they are used.
When objects move, the air around them generates a type
of friction called air resistance, or drag, that slows them down. Fast-moving
objects such as cars, trains, and aeroplanes are all streamlined –
designed with curved and sloping surfaces to cut through the air and reduce
drag. This helps them to move faster and use less fuel. Boats can be
streamlined too, to reduce water resistance.
