Direction of Friction in a Bicycle (With 3D animation)

Direction of Friction in a Bicycle (With 3D animation)


Welcome to omega open course. Many students find it difficult to determine
the direction of friction force on the tyres of a bicycle. In this video we explain the how to determine
the direction of friction on tyres in a bike. When you drive a cycle, you rotate the pedal,
which in turn rotates the chainring. The chain ring pulls the chain, which rotates
the rear sprocket, which in turn rotates the rear wheel. The friction from the ground applies force
on the wheel to stop it from slipping. This force pushes the wheel forward and cycle
moves. The moving frame of the cycle pushes the front
wheel at the axel causing it to translate in the forward direction. In order to prevent the slipping at the surface,
friction from the ground makes the wheel rotate. Now lets look at the motion in detail. The standard method to determine the direction
of friction in any scenario is to make the surface frictionless and look at the relative
motion at the point of contact. Friction will always act in the direction
opposite to the direction of relative motion. So, let’s make the surface frictionless
and look at the rear wheel first. The rotation of pedal makes the rear wheel
rotate. If you look at the point of contact, you can
see, at the point of contact tyre is moving backwards. To oppose this motion, the friction must act
on it in forward direction. It is this forward push from the friction
that moves the bike ahead. So, the friction acts in forward direction
on the rear wheel. Because of this friction, the bike moves ahead
and pushes the front wheel at its axle. This push does not provide any torque to the
front wheel and hence it can not make the wheel rotate. It only causes it to translate. Had the road been frictionless, the front
wheel would just slide on the road without rotating. If you look at the point of contact, the wheel
is moving in forward direction with respect to the road. Therefore, the direction of friction on the
front wheel must be in backward direction. It is this friction which causes the wheel
to rotate. Thus, when you drive a bicycle, the friction
acts in forward direction on rear wheel and in backward direction in front wheel. The direction is same for any vehicle in which
you or engine rotates the rear wheel like motorcycle, or rickshaw, auto rickshaw or
rear wheel drive car, bus truck etc. You may like to watch our other videos on
theories of physics. The link for the playlist is shown on the
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