---
title: "Characteristics of friction with sketch"
subject: "Applied Mechanics"
chapter: 5
key: "semester_1/applied_mechanics:characteristics-of-friction"
source: https://www.bctengineer.com/q/semester_1/applied_mechanics/characteristics-of-friction
site: BCT Engineering
---

# Characteristics of friction with sketch

Applied Mechanics · Chapter 5: Friction

- Asked in: 2068 Shrawan, 4 marks
- Video: [FRICTION in 10 Minutes! (Statics/Physics)](https://www.youtube.com/watch?v=QsWeEPaX4Vw) — Less Boring Lectures
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/applied_mechanics/characteristics-of-friction
- Whole chapter: https://www.bctengineer.com/md/semester_1/applied_mechanics/chapter-5

## Question

Explain the characteristics of friction with sketch.

## Short answer

Friction opposes relative motion and acts tangentially; it is self-adjusting up to a limiting value F_max = μ_s N, proportional to normal reaction. It is independent of contact area, depends on surface roughness, and kinetic friction is less than limiting static friction (μ_k < μ_s).

## Answer

**Friction** is the resisting force that acts tangentially at the surfaces of two bodies in contact and opposes their relative motion, or the tendency to motion.

#### Characteristics
1. It acts along the common tangent to the contact surfaces and opposes the motion (or its tendency).
2. It is a **passive, self-adjusting force**: it increases with the applied force from zero to a limiting value, F ≤ μₛN.
3. The limiting value is proportional to the normal reaction: F_max = μₛN.
4. It is independent of the area of contact.
5. It depends on the nature, roughness and condition (dry, lubricated) of the surfaces.
6. Kinetic friction is smaller than limiting static friction (μₖ < μₛ), and is almost independent of the speed.
7. It converts mechanical energy into heat and causes wear.

```text
          W
          |
   P ---> [ block ] ---> motion tendency
   <------ F ------ (friction opposes)
 =========================  rough surface
          ^ N
```
The resultant of N and F makes an angle with the normal; its maximum value is the angle of friction φ = tan⁻¹ μₛ.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which describes friction as a passive, self-adjusting force?
   A. It increases with applied force from zero up to a limiting value
   B. It always has the value mu_s N
   C. It acts along the normal to the surface
   D. It acts in the direction of motion
   Answer: A. Friction only responds to the applied force, up to F <= mu_s N. (Key point: Nature of friction force)

2. Along which direction does friction act?
   A. Along the normal reaction
   B. Along the common tangent of the surfaces, opposing the motion or its tendency
   C. In the direction of motion
   D. Along the weight
   Answer: B. Friction is tangential and opposes relative motion or its tendency. (Key point: Direction of friction)

3. Which factors affect friction?
   A. Contact area and speed
   B. Contact area only
   C. Nature and roughness of surfaces, not contact area
   D. Weight of the body only, not surface nature
   Answer: C. Friction depends on the surface nature and condition and on N, but is independent of area. (Key point: Contact area and condition)

4. What happens to the mechanical energy lost to friction?
   A. It is stored as elastic energy
   B. It is converted to potential energy
   C. It is not lost
   D. It is converted to heat and causes wear
   Answer: D. Friction dissipates mechanical energy as heat and wears surfaces. (Key point: Energy effect)