Question

1. Friction is the force which opposes the relative motion between two surfaces in contact with each other. What is a limiting static friction? State the laws related to this.

2. Show that the coefficient of friction is equal to the tan of the angle between the resultant and normal reactions.

3. For a body of mass 5kg on a plane at a limiting static friction of 30 degrees. What is the force of friction?

Answer 1

1. The maximum value of static friction is called limiting static friction.

• The magnitude of the limiting friction is independent of the area of contact between the surfaces.
• The limiting static friction is directly proportional to the normal reaction R.

ie f α R

f_s = µ_sR.

2. Angle of friction is the angle whose tangent gives the coefficient of friction.

Consider a body placed on a surface. Let N be the normal reaction and limit is the limiting friction. Let ‘θ’ be the angle between Resultant vector and normal reaction. From the triangle OBC,

∴ tanθ = µ.

3. Tangent of the angle coefficient of friction.

µ_s = tanθ

µ_s = tan 30

µ_s = 1/√3

Friction F = µ_smg

= 1/√3 × 5 × 10

F = \(\frac{50}{\sqrt 3}\)N.