Physics: Chapter 3 - Forces and Pressure

3.1 Forces

A force is a push or a pull that one object exerts on another.
It produces or tends to produce motion, and stops or tends to stop motion.

SI Unit: newton (N)

3.2 Scalars and Vectors
Scalar quantities are physical quantities that have magnitude only
Vector quantities, however, are physical quantities that possess both magnitude and direction.

3.3 Forces and Motion
A force can cause:

1. A stationary object to start moving
2. A moving object to increase speed
3. A moving object to decrease speed
4. A moving object to change its direction of motion

Forces and Zero acceleration

For an object with zero acceleration, the different forces acting on it are balanced or add up to zero.

Balanced forces and Newton's First Law

Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state.

Unbalanced forces and Newton's Second Law

When a resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force.
The product of the mass and acceleration of the object is equal to the resultant force.

F = ma
Force = mass(acceleration)

SI Unit: Newton (N)

Weight is a force
W = mg

Newton's Third Law

For every action, there is an equal and opposite reaction, and these forces act on mutually opposite bodies.

3.4 Friction and its Effects
Friction always opposes motion between two surface in contact.

3.5 Pressure
Pressure = force / area
P = F/ A
SI Unit: newton per square metre (N m^-2)