NEWTON’S LAWS OF MOTION

3. FORCES
Key notes:
1. A force may produce a change in the shape and size of an object.
2. Below the limit of proportionality, the extension of a spring is directly
proportional to the force applied on it.
3. The unit for force is the newton (N).
4. In changing the motion of an object, a force can cause it to start moving, to
accelerate or decelerate, to change its direction of motion.
5. NEWTON’S LAWS OF MOTION:
a) Newton’s first law of motion states that an object a rest will remain at rest
b) An object moving with a uniform velocity will continue to do so UNLESS a
resultant or net force acts on it.
6. Inertia is the tendency for a body to resist any change to its motion (i.e.
whether it is stationary or moving with a uniform velocity.)
7. The greater the mass, the larger the inertia.
8. Newton’s second law states that: The acceleration of an object is directly
proportional to the force applied on it.
9. Friction is a force that opposes motion. Its direction is always opposite to the
direction of motion.
10. Friction depends on the nature of the surfaces in contact, the force pressing the
two surfaces together.
11. Friction does not depend on the surface area in contact.
12. Friction can be an advantage or a disadvantage.
13. The mass of an object is the amount of matter it contains. It is always constant
and does not change when gravity changes.
14. The weight of an object is the force due to gravity acting on the object.
15. The weight of an object is not constant but depends on the gravitational
attraction.
Formulas:
 Hooke’s law: F ∝ e
O LEVEL PHYSICS REVISION NOTES
F = ke
F - force
k - F / e (spring constant)
e - extension
 Newton’s Second Law of Motion,
F = ma
force = mass x acceleration
 weight = mass x acceleration due to gravity
W = mg - measured in newtons (N)