Exploring Forces
A force is simply a push or a pull on an object. The Class 8 Curiosity chapter “Exploring Forces” looks at how forces arise — some need contact, like muscular force and friction, while others act from a distance, like gravity, magnetism and electric charge — and at what forces can do: change an object's speed, direction, or shape. It also introduces balanced and unbalanced forces.
Learning objectives
- Describe a force as a push or a pull with size and direction.
- Distinguish contact forces from non-contact forces with examples.
- List the effects a force can have on an object.
- Explain balanced and unbalanced forces in everyday situations.
Key concepts
What is a force?
A force is a push or a pull that one object exerts on another. A force has both a size (magnitude) and a direction, so the way it acts matters. When two forces act along the same line, they add up if they point the same way and partly cancel if they point opposite ways.
Contact forces
Contact forces act only when objects touch. Muscular force is applied by our muscles, as when we lift a bag. Friction is the force between two surfaces in contact that opposes their relative motion, like the grip that lets us walk or that slows a rolling ball.
Non-contact forces
Non-contact forces act without touching. Gravitational force pulls objects toward the Earth, magnetic force acts between magnets and magnetic materials, and electrostatic force acts between charged objects. A comb rubbed on hair attracting tiny paper bits shows the electrostatic force at a distance.
Effects of a force
A force can make a stationary object move, stop a moving object, speed it up or slow it down, change its direction, or change its shape. Pressing a lump of dough changes its shape, while kicking a ball at an angle changes both its speed and direction.
Balanced and unbalanced forces
When forces on an object are equal and opposite, they are balanced and the object's motion does not change. When they do not cancel, the net force is unbalanced and it changes the object's state of motion — starting, stopping, speeding up, slowing down, or turning it.
Key definitions
- Force
- A push or a pull on an object, having both magnitude and direction.
- Contact force
- A force that acts only when two objects are in physical contact, such as muscular force or friction.
- Non-contact force
- A force that acts without contact, such as gravitational, magnetic or electrostatic force.
- Balanced forces
- Forces on an object that are equal and opposite, producing no change in its motion.
Solved examples
Q1. Classify as contact or non-contact: (a) friction, (b) gravity, (c) magnetic force.
Solution: (a) friction — contact; (b) gravity — non-contact; (c) magnetic force — non-contact.
Q2. A football is kicked and curves to the right. Which effects of force are seen?
Solution: The force changes the ball's speed (it moves faster) and its direction (it curves), showing two effects at once.
Q3. Two teams pull a rope with equal force and the rope does not move. Why?
Solution: The forces are equal and opposite, so they are balanced; the net force is zero and there is no change in motion.
Common mistakes to avoid
- Thinking a force always means movement — a balanced force can leave an object still or change only its shape.
- Calling gravity a contact force; gravity acts at a distance, so it is non-contact.
- Forgetting that a force has direction, not just size.
- Believing only living things apply forces; magnets and charges apply forces too.
Exploring Forces — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
A force is best described as a:
Practice questions
Short answer
Give one example each of a contact and a non-contact force.
Contact: friction (or muscular force). Non-contact: gravitational (or magnetic/electrostatic) force.
List three effects a force can produce.
It can change an object's speed, its direction, or its shape (and can start or stop motion).
What are balanced forces?
Equal and opposite forces on an object whose net effect is zero, so the motion does not change.
Long answer
Explain the difference between contact and non-contact forces with two examples of each.
Contact forces act only when objects touch: muscular force (lifting a bag) and friction (a ball slowing on the ground). Non-contact forces act from a distance: gravitational force (a falling apple) and magnetic force (a magnet attracting iron). Electrostatic force, as between a charged comb and paper, is also non-contact.
Describe how forces affect the motion and shape of objects, with examples.
An unbalanced force can start a still object moving (pushing a cart), stop a moving one (braking), change its speed (pedalling faster), or change its direction (hitting a ball sideways). A force can also change shape without moving the object much, such as squeezing clay or stretching a rubber band. Balanced forces, being equal and opposite, leave the motion unchanged.
HOTS (Higher Order Thinking)
When you push a heavy almirah and it does not move, is a force acting? Explain.
Yes. You apply a force, but friction from the floor pushes back with an equal and opposite force, so the forces are balanced and there is no motion.
Why can the same kick make a ball both speed up and change direction?
A force has direction, so applying it at an angle to the ball's motion changes both how fast it moves and which way it goes — two effects from one force.
Quick revision
Revision notes
- Force = push or pull; has magnitude and direction.
- Contact forces: muscular, friction. Non-contact: gravity, magnetic, electrostatic.
- Effects: start/stop motion, change speed, direction or shape.
- Balanced forces → no change; unbalanced forces → change in motion.
Key takeaways
- Forces are either contact or non-contact.
- A force can change motion or shape.
- Only unbalanced forces change an object's state of motion.
Frequently asked questions
Is gravity a contact or non-contact force?
Non-contact — it pulls objects toward the Earth without any touching.
Can a force act without moving an object?
Yes; balanced forces leave motion unchanged, and a force can change an object's shape instead.
What is the difference between balanced and unbalanced forces?
Balanced forces cancel out and cause no change in motion; unbalanced forces have a net effect that changes motion.