Friction in Real Life: Advantages and Disadvantages

18 min

Let's begin

Is friction a friend or an enemy? A moto rider on a wet road in the rainy season needs all the friction the tyres can give. The same rider pays for fuel partly because friction and drag waste energy inside the engine and around the bike. Being able to weigh both sides is exactly what "evaluate" questions in exams ask for.

Advantages of friction

Walking and running: friction stops your feet slipping.
Braking: brake pads and tyres use friction to stop vehicles.
Moving vehicles: tyres push against the road.
Holding and gripping: you can hold a pen or a hoe, and nails and screws stay in wood.
Writing: chalk and pencil leave marks because of friction.
Lighting a match, and driving belts in machines such as maize mills.
Drag slows parachutes and lets aircraft land safely.

Disadvantages of friction

It wastes energy as heat, so machines and engines are less efficient and use more fuel.
It wears out tyres, shoe soles, brake pads and moving engine parts, which costs money to replace.
Heat from friction can damage machines if they are not lubricated or cooled.
Drag increases the fuel used by fast vehicles.

Worked example: braking on dry and wet roads

A moto travels at 15 m/s (54 km/h) and brakes hard enough to skid. The friction force is μ_kmg, so its deceleration is a = μ_kg. Take g = 9.8 m/s² and use the table from the last lesson.

Road	μ_k	Deceleration a = μ_kg	Stopping distance s = u² ÷ 2a
Dry concrete	0.7	6.9 m/s²	225 ÷ 13.7 ≈ 16 m
Wet concrete	0.5	4.9 m/s²	225 ÷ 9.8 ≈ 23 m

On a wet road, less friction means a smaller deceleration and a stopping distance about 40% longer. That is why riders must slow down and leave bigger gaps in the rain, and why bald tyres are dangerous.

Tip

For an "evaluate" question, give both sides, then a judgement

For example: "Friction in the brakes is useful because it stops the moto, but it wears the pads and produces heat, so the pads must be checked and replaced regularly."

✦

Practice

1

Give two advantages and two disadvantages of friction in a bicycle.

Show solutionHide solution

Solution: Advantages: the brakes can stop it, and the tyres grip the road. Disadvantages: the chain and bearings waste energy as heat, and the tyres and brake blocks wear out.

2

Why do people spread sand on a muddy footpath in the rainy season?

Show solutionHide solution

Solution: Sand makes the surface rougher, which increases friction so shoes and tyres can grip instead of slipping.

3

Using a = μ_kg with g = 9.8 m/s², find the skidding stopping distance of a moto at 10 m/s on a dry road (μ_k = 0.7).

Show solutionHide solution

Solution: a = 0.7 × 9.8 = 6.86 m/s². s = 10² ÷ (2 × 6.86) = 7.3 m.

4

"Friction should be removed from all machines." Do you agree?

Show solutionHide solution

Solution: No. Friction should be reduced in bearings and engines to save energy, but machines also rely on it: belts, brakes, clutches and tyres cannot work without friction.

Summary

Friction is useful for walking, gripping, braking, writing and driving belts.
Friction is a nuisance when it wastes energy as heat and wears parts away.
Wet or smooth surfaces lower μ, so braking distances grow. Control friction rather than removing it.

Sources and credits

5.1: Friction, from College Physics (1st edition) by Paul Peter Urone and Roger Hinrichs, OpenStax, hosted by LibreTexts, licensed under CC BY 4.0. Adapted by Ganzaa.

The Rwandan examples, worked examples and practice items are written by Ganzaa.

1Advantages of friction

2Disadvantages of friction

Worked example: braking on dry and wet roads

Practice

Advantages of friction

Disadvantages of friction