Force and Work
Learn the concepts of Force and Work in Physics with diagrams, flow charts, formulas, examples, and exercises in simple language.
Introduction to Force
Force is a push or pull acting on an object. It can change the position, speed, direction, or shape of an object.
F = m × a
SI Unit of Force
The SI unit of force is Newton (N).
PUSH
👦 ---------> 📦
Force changes the position of the box.
Effects of Force
- Force can move a stationary object.
- Force can stop a moving object.
- Force can change the direction of motion.
- Force can change the shape or size of an object.
Types of Force
Contact Forces
- Muscular Force
- Frictional Force
Person pushing a cart 👨 ---> 🛒 This is Contact Force.
Non-Contact Forces
- Magnetic Force
- Electrostatic Force
- Gravitational Force
🧲 ---> 🧷
Magnet attracts pin without touching.
Balanced and Unbalanced Force
| Balanced Force | Unbalanced Force |
|---|---|
| Equal forces act in opposite directions | Forces are not equal |
| No change in motion | Motion changes |
| Object remains at rest or moves uniformly | Object accelerates |
Balanced Force <--- 10N 📦 10N ---> No movement
Unbalanced Force <--- 5N 📦 15N ---> Box moves right
Friction
Friction is the force that opposes motion between two surfaces in contact.
Motion --->
📦================
<--- Friction
Advantages of Friction
- Helps us walk.
- Helps vehicles move.
- Helps writing on paper.
Disadvantages of Friction
- Produces heat.
- Causes wear and tear.
- Reduces efficiency.
Introduction to Work
Work is said to be done when a force moves an object through a distance.
W = F × d
SI Unit of Work
The SI unit of work is Joule (J).
Force --->
👦 ---------> 📦
Distance
Conditions for Work Done
- Force must act on the object.
- The object must move.
Case 1: No Movement 👦 pushing wall No movement = No work done
Positive, Negative and Zero Work
| Type | Description | Example |
|---|---|---|
| Positive Work | Force and motion are in same direction | Pushing a cart forward |
| Negative Work | Force opposite to motion | Friction |
| Zero Work | No movement | Pushing a wall |
Power
Power is the rate of doing work.
P = W / t
The SI unit of power is Watt (W).
Solved Examples
Example 1
A force of 20 N moves a box by 5 m. Find the work done.
Solution:
Given:
Force = 20 N
Distance = 5 m
Work = Force × Distance
W = 20 × 5
W = 100 Joule
Example 2
A person does 200 J work in 10 seconds. Find power.
Solution:
Power = Work / Time
P = 200 / 10
P = 20 Watt
Quick Revision Flow Chart
Practice Questions
- Define force.
- Write the formula of force.
- What is friction?
- Define work with formula.
- What is the SI unit of work?
- Differentiate balanced and unbalanced force.
- A force of 15 N moves an object by 3 m. Find work done.
- Define power.
- What are contact forces?
- Give one example of non-contact force.