- Frictional force is defined as force that opposes the motion of an object.
- Frictional force occurs whenever two surfaces are in contact with each other.
- Frictional force is in opposite direction to the moving object and it is parallel to the surface.
- Frictional force has direction and magnitude.
Direction and Magnitude of Frictional Force
- Frictional force has direction and magnitude (value) that can be measured.
- The direction of friction is opposite to the motion of the object.
- Thus, friction can :
b) Slow down and stop a moving object
Diagram 1 : Frictional force always opposes the motion of an object
- The factors that affect the magnitude of frictional force are :
a) Surface condition. The rougher the surface, the larger the frictional force.
b) Weight of object. The heavier the object, the larger its frictional force.
Examples showing the existence of force
a) Friction enables a ladder to lean against the wall without slipping.
b) Heat produced by friction lights up the match
c) Friction between soles of shoes and the road surface enables us to walk without slipping
d) Friction between the tyres and the road surface prevents the car form skidding on the road
Advantages of friction
- Enables animals to climb trees.
- Allows brakes to slow down or stop a moving vehicle.
- Enables us to hold objects.
- Produces heat to light up the match.
- Enables us to write on paper.
Disadvantages of friction
- Wastes energy.
- Slows down moving objects.
- Wears out surfaces (og. soles of shoes, machines parts, tyres).
- Produces unnecessary heat that can damage machines.
- Produces unnecessary sound.
Ways to increase friction
- Soles of shoes have rough patterns to prevent slipping while walking.
- Tyres have tread patterns or grooves to prevent vehicles from skidding.
- The rough surface of the steering wheel cover helps the driver in turning the steering wheel.
- Handles of axes, knives and scissors have rough surfaces to ensure a firmer grip on the fools.
Ways of reducing friction
- Using ball bearings
Ball bearing are placed around the axles of wheels of vehicles to reduce friction
- Using wheels
Vehicles and heavy objects such as piano, sewing machine and sofa set are fitted with wheels so that they can moved easily
- Using rollers
Conveyor belts fitted with metal rollers are used to transfer luggage in airports and heavy objects in factories
- Using lubricants such as grease and oil
Oil or grease is applied to the hinges of doors and windows to reduce friction. Engines and machines are lubricated with oil to reduce friction.
- Using a cushion of air
Friction between two surfaces can be reduced by a layer of air between them. The air puck glides easily when it is pushed. Air that comes out of the balloon forms a cushion of air puck and table surface, whereby reducing the friction between them.
The cushion of air between the hovercraft and the water surface enables hovercraft to move faster.
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