Imagine that you are a ranger at an outback national park. Off-road drivers are causing considerable soil erosion, and you are considering banning the use of motor vehicles away from the official roads. Your assistant asks whether bicycles should also be banned. A typical motor vehicle has a mass of 2000 kg, and the total area of the part of its tyres typically in contact with the ground is around 500 square centimetres. A bicycle plus rider only weighs around 100 kg, but the area of its tyres in contact with the ground is only around 5 square centimetres. Which applies a greater pressure to the ground - a motor vehicle or a bicycle?
A) Motor vehicles apply more pressure - bikes need not be banned.
B) Bicycles apply more pressure and should be banned too.
C) Bicycles and motor vehicles apply about the same amount of pressure, and so should both be banned.
D) The answer depends on the speed at which they are traveling.
E) They apply a force, not a pressure, to the ground.

Question

Quizplus · Accepted Answer

Pressure is defined as force per unit area. The weight of the vehicle or bike is the force applied to the ground, and the area of the tyres in contact with the ground is the area over which this force is distributed. A typical motor vehicle has 500/2000 = 0.25 square centimetres of tyre area per kilogram of weight, while a bicycle has 5/100 = 0.05 square centimetres of tyre area per kilogram of weight. This means that the bicycle per kilogram of weight exerts more pressure on the ground than a motor vehicle. Therefore, bicycles should be banned along with motor vehicles to minimize soil erosion.

Imagine That You Are a Ranger at an Outback National