⚙️ 1. What is Force?
A force is a push or pull acting on an object that can:
- change its speed
- change its direction
- change its shape
- stop or start motion
👉 Force is a vector quantity (has magnitude + direction)
🧭 2. Types of Forces
| Type of Force | Meaning | Example |
|---|---|---|
| Muscular Force | Force applied by muscles | Pushing a cart |
| Frictional Force | Force that opposes motion | Brakes stopping a bicycle |
| Gravitational Force | Force of attraction between objects | Falling of an apple |
| Magnetic Force | Force exerted by magnets | Magnet attracting iron pins |
| Electrostatic Force | Force between charged objects | Charged comb attracting paper bits |
| Mechanical Force | Force produced by machines | Crane lifting heavy objects |
| Contact Force | Force that acts only when objects touch | Pushing a table |
| Non-contact Force | Force that acts without touching | Magnetic force, gravitational force |
🔹 Contact Forces
Act only when objects are in physical contact:
- Frictional force
- Muscular force
- Normal force
🔹 Non-Contact Forces
Act without physical contact:
- Gravitational force
- Magnetic force
- Electrostatic force
🚗 3. Effect of Force on Motion
A force can:
- Start motion (push a stationary object)
- Stop motion (brakes in vehicles)
- Increase speed (accelerating car)
- Decrease speed (friction)
- Change direction (turning a bicycle)
🧲 4. Inertia
Inertia is the tendency of an object to resist change in its state of motion.
Types:
- Inertia of rest → object stays at rest
- Inertia of motion → object keeps moving
- Inertia of direction → object resists change in direction
👉 Heavier objects have more inertia
⚖️ 5. Newton’s First Law of Motion
An object remains at rest or in uniform motion unless acted upon by an external force.
👉 Also called Law of Inertia
🔄 6. Newton’s Second Law of Motion
Force = mass × acceleration
👉 F = m × a
Key points:
- More force → more acceleration
- More mass → less acceleration
🧱 7. Momentum
Momentum = mass × velocity
👉 p = m × v
- Depends on both mass and speed
- Unit: kg m/s
🔁 8. Conservation of Momentum
In absence of external force:
👉 Total momentum before collision = Total momentum after collision
🚶 9. Everyday Examples
- Seat belts reduce injury by increasing time of stopping
- Jumping from a moving bus shows inertia
- Cricket ball stops due to friction and force by hands
📊 10. Important Formulae
- Force = m × a
- Momentum = m × v
Newton’s Laws of Motion
| Law | Statement | Example |
|---|---|---|
| Newton’s First Law | An object remains at rest or continues to move with the same speed in a straight line unless acted upon by an external force. | A football remains still until kicked. |
| Newton’s Second Law | The force acting on an object is equal to the product of its mass and acceleration. | A light ball moves faster than a heavy ball when kicked with the same force. |
| Newton’s Third Law | For every action, there is an equal and opposite reaction. | A gun recoils backward when a bullet is fired. |
MCQs (50 Questions)
🔹 Basic Concept MCQs
1. Force is defined as:
A) Only motion
B) Push or pull
C) Energy
D) Speed
✅ B
2. SI unit of force is:
A) Joule
B) Newton
C) Watt
D) Pascal
✅ B
3. Force can change:
A) Only shape
B) Only speed
C) Motion state
D) None
✅ C
4. Force is a:
A) Scalar
B) Vector
C) Constant
D) Energy
✅ B
5. Which is a contact force?
A) Gravity
B) Magnetism
C) Friction
D) Electrostatic
✅ C
🔹 Inertia & Newton’s Laws
6. Law of inertia is Newton’s:
A) First law
B) Second law
C) Third law
D) None
✅ A
7. Inertia depends on:
A) Speed
B) Mass
C) Force
D) Time
✅ B
8. Heavier objects have:
A) Less inertia
B) More inertia
C) No inertia
D) Constant inertia
✅ B
9. Newton’s second law is:
A) F = m/v
B) F = m × a
C) F = a/m
D) F = m + a
✅ B
10. Momentum formula is:
A) m/a
B) m × v
C) v/m
D) m + v
✅ B
🔹 Applications
11. Seat belts work due to:
A) Gravity
B) Inertia
C) Speed
D) Heat
✅ B
12. Brakes stop motion due to:
A) Force
B) Friction
C) Gravity
D) Energy
✅ B
13. Unit of momentum:
A) kg m/s
B) N/m
C) J/s
D) N
✅ A
14. Non-contact force is:
A) Friction
B) Muscular
C) Gravity
D) Tension
✅ C
15. Force required depends on:
A) Mass
B) Time
C) Volume
D) Density
✅ A
Assertion–Reason Test (15 Questions)
1. Assertion: Force changes motion.
Reason: Force can change speed or direction.
A) Both true, R explains A
✅ A
2. Assertion: Inertia depends on mass.
Reason: Greater mass means greater resistance to change.
A) Both true, R explains A
✅ A
3. Assertion: Newton’s first law is law of force.
Reason: It explains inertia.
A) A false, R true
✅ A
4. Assertion: Momentum is conserved in absence of external force.
Reason: No net force means no change in total momentum.
A) Both true, R explains A
✅ A
5. Assertion: Friction is a non-contact force.
Reason: It acts without contact.
A) A false, R false
✅ C (Friction is contact force)
Numericals Worksheet
🔹 Easy Level
1. A force of 10 N acts on a mass of 2 kg. Find acceleration.
F = ma → a = 10/2 = 5 m/s²
2. Mass = 5 kg, velocity = 4 m/s. Find momentum.
p = mv = 5 × 4 = 20 kg m/s
🔹 Moderate Level
3. A body accelerates at 3 m/s² under force of 15 N. Find mass.
m = F/a = 15/3 = 5 kg
4. Momentum changes from 20 to 0 in 4 s. Find rate of change.
= 20/4 = 5 N (force)
🔹 Higher Level
5. A 10 kg object moves at 6 m/s. Force stops it in 3 s. Find force.
Initial momentum = 60
Final = 0
F = (60)/3 = 20 N (opposite direction)
Fill in the Blanks
- A push or pull is called ________.
➡️ Force - SI unit of force is ________.
➡️ Newton - Force is a ________ quantity.
➡️ Vector - Force can change the ________, speed or direction of motion.
➡️ State - Force that acts without physical contact is called ________ force.
➡️ Non-contact - Force between two surfaces in contact is called ________ force.
➡️ Contact - Friction is a ________ force.
➡️ Contact - Inertia is the tendency of an object to resist change in its ________.
➡️ State of motion - Heavier objects have more ________.
➡️ Inertia - Newton’s first law is also called law of ________.
➡️ Inertia - Newton’s second law gives relation between force, mass and ________.
➡️ Acceleration - Formula of force is F = m × ________.
➡️ a - Momentum is the product of mass and ________.
➡️ velocity - Formula of momentum is p = m × ________.
➡️ v - SI unit of momentum is ________.
➡️ kg m/s - In absence of external force, momentum remains ________.
➡️ constant - Force can ________ or stop motion.
➡️ start - Gravitational force is a ________ force.
➡️ non-contact - Muscular force is a ________ force.
➡️ contact - Seat belts work due to ________.
➡️ inertia