Kinetic Friction

Friction is a force which resists motion when two objects are placed in contact with each other. Kinetic friction is the force of friction which is caused when two objects are relatively in motion with each other. The characteristic of kinetic friction on a particular surface is measured by the coefficient of kinetic friction represented as ‘µ_k’. The kinetic friction between two solid objects is known as sliding friction and the kinetic friction between solid and a liquid or a gas is known as fluid friction.

Example 1: An object of mass 50kg is being pushed on the ground. If the coefficient of kinetic friction is 0.25, then what is the force of kinetic friction acting on the object?(g = 9.8m/sec²)

Kinetic friction, f_k = μ_k * N

Here, μ_k = coefficient of kinetic friction

N = Normal force = Weight of the object = (mass) * (gravity) = 50kg * 9.8m/sec² = 490N

So, f_k = (0.25) * (490N) ==>f_k = 122.5N

Therefore the kinetic frictional force, f_k = 122.5N

Example 2: The kinetic frictional force acting on an object of mass 24kg is 132N. What is the coefficient of kinetic friction on the object?

Kinetic friction, f_k = μ_k * N

Given: kinetic frictional force, f_k = 132N

N = Normal force = Weight of the object = (mass) * (gravity) = 24kg * 9.8m/sec² = 235.2N

So, f_k = (μ_k) * (235.2N) ==> 132 = μ_k * (235.2N) ==>μ_k = (132)/ (235.2) = 0.561

Therefore the coefficient of kinetic friction, μ_k = 0.561

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Kinetic Friction

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