Chapter 5: Exploring Forces
Original notes — ready CBSE (NCERT, English Medium) • Class 8 • Science • Book: Curiosity
Chapter 5: Exploring Forces — EG's own notes, in simple words
Book: Curiosity (CBSE, Class 8) | Chapter 5 | Medium: English
Diagram (labels are printed on the image): Diagram (labels are printed on the image): a push on a box, friction opposing the motion, and gravity pulling a ball down. A general picture about forces, not a diagram from the book.
A magnet attracting nails and a stretched spring. A general picture about magnetic and muscular forces, not a book scene.
What the chapter is about
A force is a push or a pull. We use forces every day — to open a door, kick a ball, lift a bag or stop a moving cycle. A force can change the speed of an object, change its direction, change its shape, or start or stop its motion.
Forces can act by contact or without contact. Muscular force and friction act when objects touch. Friction opposes motion — it is why a ball rolling on the ground slows down. Magnetic force, electrostatic force and gravitational force act without contact: a magnet pulls iron from a distance, and the Earth pulls everything towards itself.
When two forces act on an object, the result depends on their sizes and directions. If they are equal and opposite, they are balanced and the object stays at rest or keeps moving steadily. If they are unequal, they are unbalanced and the object's motion changes.
What you should learn
Notice what a force can do, the difference between contact and non-contact forces, and how balanced and unbalanced forces affect motion.
Key Terms
- Force — A push or a pull that can change the motion, direction or shape of an object.
- Friction — The force that opposes motion when two surfaces rub against each other.
- Gravitational force — The force with which the Earth (or any mass) attracts objects towards itself.
- Magnetic force — The force of attraction or repulsion between magnets, acting without contact.
- Balanced forces — Equal and opposite forces acting on an object, which do not change its state of motion.
Remember
- A force can start, stop, speed up, slow down or change the direction or shape of an object.
- Friction always opposes motion between surfaces in contact.
- Magnetic, electrostatic and gravitational forces act without contact.
- Balanced forces do not change motion; unbalanced forces do.
Exam Tip / Common Mistake
Common mistake: saying friction helps motion. Friction opposes motion — it slows moving objects down, though it also helps us walk and grip things without slipping.
Chart / Table: Kinds of forces
| Point | Detail |
|---|---|
| Muscular force | Contact force; from muscles of the body |
| Friction | Contact force; opposes motion between surfaces |
| Magnetic force | Non-contact; attraction or repulsion by magnets |
| Electrostatic force | Non-contact; between charged objects |
| Gravitational force | Non-contact; Earth pulls objects towards itself |
Practice set — try it yourself
- What is a force? Give two examples.
Hint: Think of a push and a pull. - Why does a rolling ball slow down and stop?
Hint: Think about the force between the ball and the ground. - Name two contact forces and two non-contact forces.
Hint: Think about touch and distance. - What happens when balanced forces act on an object at rest?
Hint: Think about equal and opposite forces. - Why does a dropped object fall to the ground?
Hint: Think about the Earth's pull.
Questions with Answers
- What can a force do to an object?
A force can make a resting object move, stop a moving object, change its speed or direction, or change its shape — for example, stretching a spring or squeezing a rubber ball. - What is friction? Is it useful or harmful?
Friction is the force that opposes motion when two surfaces are in contact. It is both: it slows moving objects, which can be unwanted, but it also lets us walk, grip objects and stop vehicles. - Give examples of non-contact forces.
Magnetic force (a magnet attracting iron), electrostatic force (a charged comb attracting bits of paper) and gravitational force (the Earth pulling a falling apple) all act without the objects touching. - What is the difference between balanced and unbalanced forces?
Balanced forces are equal in size and opposite in direction, so they do not change an object's motion. Unbalanced forces are unequal, so they change the object's speed or direction. - A box is pushed but does not move. Explain in terms of forces.
The push is balanced by friction between the box and the surface. Because the forces are equal and opposite, there is no change in motion, so the box stays at rest.
How to use this page: Read the summary, say the Key Terms in your own words, then try the practice set without looking. Use the Questions with Answers to check yourself afterwards. Ask your teacher or parent to check your answers.