PHYSICS
NEWTON'S LAWS OF MOTION
Newton's three laws of motion are the basic principles of classical mechanics. They describe how forces affect the motion of objects.
Newton's First Law — Law of Inertia
An object at rest stays at rest, and an object in motion stays in motion at a constant speed in a straight line, unless an outside force acts on it.
Inertia is the tendency of an object to resist changes in its motion.
Example:
A soccer ball stays still on the grass until someone kicks it.
Newton's Second Law — Force and Acceleration
The acceleration of an object depends on the net force acting on it and its mass.
Formula:
F = ma
Where:
- F = force
- m = mass
- a = acceleration
A greater force produces greater acceleration, while a greater mass requires more force to produce the same acceleration.
Example:
A light box requires less force to accelerate quickly, while a heavy box requires more force to accelerate at the same rate.
Newton's Third Law — Action and Reaction
For every action force, there is an equal and opposite reaction force.
When one object pushes or pulls another object, the second object pushes or pulls back with the same amount of force in the opposite direction.
The two forces act on different objects.
Example:
When you jump off a small boat, you push the boat backward, while the boat pushes you forward.
Quick Review
1st Law → Inertia
Objects resist changes in motion.
2nd Law → F = ma
Force causes acceleration.
3rd Law → Action and Reaction
Forces come in equal and opposite pairs.
Work, Energy, and Power
Work is the transfer of energy by a force acting through a displacement.
Energy is the capacity to do work or cause a change.
Power is the rate at which work is done or energy is transferred.
Work
Definition:
Work is done when a force moves an object over a distance in the direction of that force.
Formula:
W = Fd cos(θ)
Where:
- W = work
- F = force
- d = displacement
- θ = angle between the force and displacement
Unit: Joule (J)
1 J = 1 N·m
Nature:
Work is a scalar quantity, meaning it has magnitude but no direction.
Energy
Definition:
Energy is the ability or capacity to do work or cause a change.
Kinetic Energy
Kinetic energy is the energy of motion.
Formula:
KE = ½mv²
Where:
- KE = kinetic energy
- m = mass
- v = velocity
Potential Energy
Potential energy is stored energy based on an object's position.
For gravitational potential energy:
PE = mgh
Where:
- PE = potential energy
- m = mass
- g = acceleration due to gravity
- h = height
Unit: Joule (J)
Power
Definition:
Power measures how fast work is done or energy is transferred.
Formula:
P = W/t
or
P = Fv
Where:
- P = power
- W = work
- t = time
- F = force
- v = velocity
Unit: Watt (W)
1 W = 1 J/s
Quick Review
Work → transfer of energy by force
Energy → ability to do work
Power → rate of doing work
Work → Joule (J)
Energy → Joule (J)
Power → Watt (W)