1. Introduction
A force is a push or pull on an object. Forces are everywhere around us—they can change the motion of an object, deform it, or cause it to rotate. Understanding forces is essential to explain the motion and interaction of objects in daily life.
2. Types of Forces
Contact Forces
These forces act when two objects are in physical contact. Examples:
- Frictional Force: Opposes motion between two surfaces.
- Tension Force: Force transmitted through a string, rope, or cable.
- Applied Force: A push or pull applied by a person or object.
- Normal Force: Perpendicular force exerted by a surface on an object.
Non-Contact Forces
These forces act even when objects are not touching. Examples:
- Gravitational Force: Pulls objects toward the Earth.
- Magnetic Force: Acts between magnets or magnetic materials.
- Electrostatic Force: Acts between electrically charged objects.
3. Effects of Forces
- Change in Speed: Force can accelerate or decelerate an object.
- Change in Direction: A force can change the direction of an object’s motion.
- Deformation: Objects can be stretched, compressed, or twisted.
- Rotation: Torque or couple can cause rotation of objects.
4. Balanced and Unbalanced Forces
- Balanced Forces: Forces acting on an object that cancel each other. No change in motion occurs.
- Unbalanced Forces: Forces that do not cancel each other. They cause a change in motion or acceleration.
5. Friction
- Definition: A force that opposes motion between two surfaces in contact.
- Factors affecting friction: Surface roughness and nature of materials.
- Advantages of friction: Helps in walking, writing, and driving vehicles.
- Disadvantages of friction: Causes wear and tear and energy loss.
6. Gravity
- A force that pulls objects toward the center of the Earth.
- Causes objects to fall and gives them weight.
- Gravitational force acts on all objects, regardless of shape or size.
7. Magnetic and Electrostatic Forces
- Magnetic Force: Acts between magnets or magnetic materials without contact.
- Electrostatic Force: Acts between charged bodies. Can attract or repel.
8. Measurement of Force
- Force is measured using a spring balance.
- Unit of Force: Newton (N)
- 1 Newton = Force required to accelerate 1 kg mass by 1 m/s²
9. Key Terms
| Term | Meaning |
|---|---|
| Force | Push or pull on an object |
| Contact Force | Force that acts through direct contact |
| Non-Contact Force | Force that acts at a distance |
| Friction | Force opposing motion between surfaces |
| Gravitational Force | Force that pulls objects toward Earth |
| Balanced Force | Forces cancel each other; no motion change |
| Unbalanced Force | Forces do not cancel; motion changes |
| Newton | SI unit of force |
10. Examples of Forces in Daily Life
- Pushing a bicycle → Applied force
- Rolling a ball → Applied force and friction
- Dropping an apple → Gravitational force
- Using a magnet → Magnetic force
- Rubbing hands → Friction
- Balloon sticking to wall → Electrostatic force
11. Possible Questions
Very Short Answer Questions (1–2 marks)
- Define force.
- Name two contact forces.
- Give one example of non-contact force.
- What is the unit of force?
- Define friction.
Short Answer Questions (3–5 marks)
- Explain the difference between balanced and unbalanced forces.
- List two advantages and two disadvantages of friction.
- Describe the effect of force on an object.
- How is force measured?
Long Answer Questions (6–8 marks)
- Explain the types of forces with examples.
- Discuss the importance of friction in daily life.
- Describe gravitational, magnetic, and electrostatic forces with examples.
- Illustrate balanced and unbalanced forces with diagrams.
Multiple Choice Questions (MCQs)
- Force is measured in:
a) Joule
b) Newton
c) Watt
d) Pascal
Answer: b - Which is a contact force?
a) Gravity
b) Magnetism
c) Friction
d) Electrostatic
Answer: c - Unbalanced forces cause:
a) No motion
b) Change in motion
c) Opposite forces
d) Balanced motion
Answer: b
Fill in the Blanks
- Friction opposes _______.
- Gravity gives objects their _______.
- A push or pull on an object is called _______.
True/False Questions
- Friction always helps motion. False
- Magnetic force is a non-contact force. True
- Balanced forces change the motion of an object. False
Match the Following
| Column A | Column B |
|---|---|
| Gravity | Pulls objects toward Earth |
| Friction | Opposes motion |
| Magnetism | Acts at a distance |
| Spring balance | Measures force |
| Electrostatic | Acts between charged bodies |
Electric Current and Forces Basics
- A force is defined as:
a) Energy
b) Push or pull on an object
c) Speed of an object
d) Acceleration
Answer: b - Unit of force is:
a) Joule
b) Watt
c) Newton
d) Pascal
Answer: c - Force can cause:
a) Motion
b) Change in shape
c) Both motion and deformation
d) None of these
Answer: c - Which of these is a contact force?
a) Gravity
b) Friction
c) Magnetic force
d) Electrostatic force
Answer: b - Which of these is a non-contact force?
a) Tension
b) Friction
c) Gravity
d) Applied force
Answer: c
Contact Forces
- Friction opposes:
a) Motion of objects
b) Gravity
c) Magnetic field
d) None of these
Answer: a - Tension is:
a) Pull along a rope or string
b) Push along a rope
c) Magnetic effect
d) Gravitational pull
Answer: a - Applied force is:
a) Force applied by a person or object
b) Force of friction
c) Gravitational force
d) Magnetic force
Answer: a - Normal force acts:
a) Parallel to the surface
b) Perpendicular to the surface
c) Opposite to friction
d) Along gravity
Answer: b - A student pushes a table with constant force. Which force opposes the motion?
a) Tension
b) Friction
c) Gravity
d) Magnetic force
Answer: b
Non-Contact Forces
- Gravitational force pulls objects:
a) Toward Earth
b) Away from Earth
c) Sideways
d) Randomly
Answer: a - Magnetic force acts:
a) Only in contact
b) At a distance
c) Only with copper
d) Only when touching iron
Answer: b - Electrostatic force acts between:
a) Magnetic metals
b) Charged bodies
c) Conductors
d) Friction surfaces
Answer: b - Gravity affects:
a) All objects
b) Only heavy objects
c) Only light objects
d) None of these
Answer: a - Magnetic force is maximum:
a) At a distance from magnets
b) Close to magnets
c) In insulators
d) In metals only
Answer: b
Friction
- Friction is helpful in:
a) Walking
b) Writing
c) Driving vehicles
d) All of the above
Answer: d - Friction is harmful because it:
a) Helps movement
b) Causes wear and tear
c) Supports motion
d) None of these
Answer: b - Factors affecting friction include:
a) Surface roughness
b) Nature of materials
c) Both a and b
d) Color of object
Answer: c - Sliding friction occurs when:
a) Object rolls
b) Object slides
c) Object floats
d) Object falls
Answer: b - Rolling friction is generally:
a) Greater than sliding friction
b) Less than sliding friction
c) Equal to sliding friction
d) Zero
Answer: b
Balanced and Unbalanced Forces
- Balanced forces:
a) Cause acceleration
b) Do not change motion
c) Cause rotation only
d) Increase speed
Answer: b - Unbalanced forces:
a) Cancel each other
b) Change motion or speed
c) Never act
d) Are always magnetic
Answer: b - Two equal and opposite forces act on an object. Motion will:
a) Increase
b) Decrease
c) Not change
d) Rotate only
Answer: c - A moving object slows down due to:
a) Balanced forces
b) Unbalanced forces like friction
c) Gravity alone
d) Tension
Answer: b - Balanced forces can:
a) Keep an object at rest
b) Keep an object moving at constant speed
c) Both a and b
d) None of these
Answer: c
Gravity
- Weight of an object is due to:
a) Tension
b) Gravity
c) Friction
d) Magnetic force
Answer: b - Gravitational force acts:
a) Only on Earth
b) On all objects with mass
c) Only on metals
d) Only on living things
Answer: b - Acceleration due to gravity on Earth is:
a) 5 m/s²
b) 9.8 m/s²
c) 10 m/s² exactly
d) 1 m/s²
Answer: b - Free fall is motion due to:
a) Applied force
b) Gravity alone
c) Friction
d) Magnetic force
Answer: b - Heavier objects fall faster than lighter ones in vacuum:
a) True
b) False
Answer: b
Magnetic and Electrostatic Forces
- Magnetic force acts:
a) Only on metals
b) Only in friction
c) At a distance without contact
d) Only when touching iron
Answer: c - Like charges ______ each other.
a) Attract
b) Repel
c) Neutralize
d) Rotate
Answer: b - Unlike charges ______ each other.
a) Attract
b) Repel
c) Neutralize
d) Spin
Answer: a - A magnet attracts:
a) Wood
b) Iron
c) Plastic
d) Rubber
Answer: b - Electrostatic force can:
a) Attract or repel
b) Only attract
c) Only repel
d) Never act
Answer: a
Measurement of Force
- Force is measured using:
a) Spring balance
b) Ruler
c) Stopwatch
d) Voltmeter
Answer: a - 1 Newton is the force required to:
a) Accelerate 1 kg mass by 1 m/s²
b) Stop 1 kg mass
c) Push 1 kg mass slowly
d) Lift 1 kg mass
Answer: a - Spring balance works due to:
a) Magnetic effect
b) Stretching of spring
c) Friction
d) Gravity only
Answer: b - Weight is measured in:
a) Newtons
b) Kilograms
c) Joules
d) Amperes
Answer: a - Tension in a rope is measured using:
a) Voltmeter
b) Ammeter
c) Spring balance
d) Thermometer
Answer: c
Applications
- Friction helps in:
a) Walking
b) Driving cars
c) Writing
d) All of these
Answer: d - Magnetic forces are used in:
a) Electric bell
b) Maglev train
c) Magnetic crane
d) All of the above
Answer: d - Electrostatic forces are used in:
a) Photocopiers
b) Air purifiers
c) Both a and b
d) None of these
Answer: c - Friction can be reduced by:
a) Lubricants
b) Polishing surfaces
c) Both a and b
d) Heating surfaces
Answer: c - Gravitational force is important because:
a) Gives weight
b) Keeps planets in orbit
c) Causes free fall
d) All of the above
Answer: d
True/False
- Friction always hinders motion. False
- Gravitational force acts only on moving objects. False
- Electrostatic force can attract or repel. True
- Balanced forces can change the speed of an object. False
- Spring balance measures force in Newtons. True