# The limiting frictional force between…..

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The limiting frictional force between two surfaces depends on

• I. The normal reaction between the surfaces
• II. The area of surface in contact
• III. The relative velocity between the surfaces
• IV. The nature of the surface

A. I only

B. I & IV only

C. II only

D. III only

B

## DETAILS…

Frictional force = coefficient of friction X normal reaction

From this expression, it is clear that limiting frictional force depends on:

• The coefficient of friction which depends on the nature of the surface and is zero for a perfectly smooth surface.
• The normal reaction, which is the weight of the body involved.

Now for the right answer to the above question:

1. Option A is incorrect. I is correct, but IV is also correct.
2. Option B is correct. limiting frictional force depends on the nature of the contact surface and the normal reaction.
3. C is incorrect. the area of the contacting surface does not matter.
4. D is not the correct answer. the relative velocity between the surfaces does not matter.

## KEY-POINTS…

• Limiting friction depends on the nature of the contacting surfaces, that is why in physics, smooth bodies are assumed to be frictionless.
• Limiting friction also depends on the weight of the top contact object, the higher the weight, the higher the frictional force experienced.
• The limiting frictional force between two surfaces does not depend on the surface area in contact, neither does it depend on their relative velocities.

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