Force and Laws of Motion 9 Science — Revision Notes
Force is a push or pull that can change an object's motion or shape. Newton's laws of motion explain how objects move and interact, forming the foundation
TL;DR: Force is a push or pull that can change an object's motion or shape. Newton's laws of motion explain how objects move and interact, forming the founda…
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Force is a push or pull that can change an object's motion or shape. Newton's laws of motion explain how objects move and interact, forming the foundation
Newton's First Law of Motion
- Object in motion stays in motion; object at rest stays at rest unless acted upon by external force
- This law defines inertia: resistance of object to change in motion
- Inertia depends on mass: greater mass means greater inertia
Newton's Second Law of Motion
- Force = mass × acceleration (F = ma)
- Acceleration is directly proportional to force and inversely proportional to mass
- Direction of acceleration is same as direction of applied force
Newton's Third Law of Motion
- Every action has equal and opposite reaction
- Forces always occur in pairs acting on different bodies
- Action-reaction forces are equal in magnitude but opposite in direction
Types of Forces
- Contact forces: friction, normal force, tension, applied force (require direct contact)
- Non-contact forces: gravitational, magnetic, electrostatic (act without direct contact)
- Friction: opposes motion, depends on surface roughness and normal force
Momentum and Impulse
- Momentum: p = mv (mass × velocity), vector quantity
- Impulse: F × t = change in momentum
- Law of conservation of momentum: total momentum before = total momentum after collision
Key Terms
- Force: Push or pull that can change motion or shape of object
- Inertia: Resistance of object to change in its state of motion
- Momentum: Product of mass and velocity of an object
- Friction: Force opposing relative motion between two surfaces
- Impulse: Product of force and time duration of force application
Frequently Asked Questions
Why does a seatbelt prevent injury during sudden braking?
Seatbelt applies force to change momentum gradually, reducing the rate of change of velocity (acceleration) and thus injury risk.
What is the difference between mass and weight?
Mass is amount of matter (constant), weight is gravitational force on mass (W = mg, varies with gravity).
In a collision between two balls, why do both experience the same force if they have different masses?
By Newton's third law, forces are equal and opposite; different masses result in different accelerations.
More 9 Science Revision Notes
- Matter in Our Surroundings
- Is Matter Around Us Pure
- Atoms and Molecules
- Structure of the Atom
- The Fundamental Unit of Life
- Work and Energy
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