How Forces Affect Motion
Class 9 · Science
3 ideas in Class 9 Science, explained in plain words, with games and quizzes to practise.
Forces, Net Force and Friction
Part of: Forces, Net Force and Friction
A force can change motion or shape. When forces oppose each other, compare their sizes to find the net force. Friction acts between touching surfaces and opposes sliding.
Why it matters. Understanding net force helps explain why an object starts, slows or keeps moving. Friction can help movement, but it can also resist it.
Try it in two minutes
- Push a book gently across a table.
- Ask what force opposes the push.
- Try a smoother surface and compare how far it moves.
Try at home. Notice where friction helps your shoes grip the ground.
Inertia and Newton’s First Law
Part of: Inertia and Newton’s First Law
Inertia is an object’s tendency to resist a change in its motion. With zero net force, an object stays at rest or continues at constant velocity in a straight line.
Why it matters. This idea explains why motion does not need a continuing push when opposing forces are absent or balanced.
Try it in two minutes
- Place a small object on a smooth surface.
- Give it a gentle push and watch it move.
- Name forces that could gradually slow it in a real room.
Try at home. When a moving toy slows, look for an opposing force rather than assuming motion needs a forward push.
Newton’s Second and Third Laws
Part of: Newton’s Second and Third Laws
The second law links net force, mass and acceleration: a larger net force gives greater acceleration, while more mass gives less acceleration for the same force. The third law says interacting objects exert equal and opposite forces on each other.
Why it matters. These laws explain how pushes change motion and why interacting objects both experience forces.
Try it in two minutes
- Roll an empty cart and then a loaded cart with a similar push.
- Compare how their motion changes.
- Push gently against a sturdy wall and notice the wall pushes back.
Try at home. Look for the two interacting objects whenever you identify an action-reaction pair.
What your child will practise
- Forces, Net Force and Friction: Candy Quick Fire (Quick Fire)
- Forces, Net Force and Friction: Lab Explorer Sort (Sort It Out)
- Forces, Net Force and Friction: Ocean Puzzle (Clue Puzzle)
- Inertia and Newton’s First Law: Desert Quick Fire (Quick Fire)
- Newton’s Second and Third Laws: Mission Control Quest (Collect the Answer)
- Quiz: Forces, Net Force and Friction (8 questions)
- Quiz: Inertia and Newton’s First Law (8 questions)
- Quiz: Newton’s Second and Third Laws (8 questions)