Work Done
Work (W) is done when a force acts on an object moving it from one position to another. Energy is transferred, calculated as:
W = F \times s
Where:

W = Work done (Joules)
F = Force applied (N)
s = Distance moved (m)

Work is done against friction, even if energy is wasted as thermal energy.

1 Joule of work is done when a force of 1 Newton moves an object 1 meter.

Calculating Forces and Equilibrium

Scale Drawings
Useful for visualizing and calculating resultant forces.

Draw forces to scale 'tip-to-tail' and measure resultant force.

Equilibrium
An object is in equilibrium if the resultant force is zero.

On scale diagrams, this forms a closed loop (e.g., triangle).

Component Forces
Forces can act at angles; they can be resolved into perpendicular components (e.g., horizontal and vertical).

This simplifies calculations and understanding of how forces interact.

Key Examples
A skydiver experiences weight pulling down and air resistance acting upwards. The resultant force determines their acceleration and motion.
A man on an electric bicycle experiences forces: a driving force of 4 N north and wind resistance of 3 N east. The resultant force can be calculated using scale drawings and

Contact and Non-Contact Forces

Definition of Force

A force is a push or pull on an object caused by its interaction with something.

Vector Quantities

Force is a vector quantity, meaning it has both magnitude and direction.
Examples of vector quantities include:

Force
Velocity
Displacement
Acceleration
Momentum

Scalar quantities (only have magnitude):

Speed
Distance
Mass
Temperature
Time

Representation of Vectors

Vectors are often represented by arrows; length indicates magnitude, direction indicates direction.

Contact Forces

Require two objects to be touching.
Examples:

Friction
Air resistance
Tension in ropes
Normal contact force

Non-Contact Forces

Do not require contact to act.
Examples:

Gravitational force
Magnetic force
Electrostatic force

Newton's Third Law

When two objects interact, they exert equal and opposite forces on each other.
Example: The Sun and Earth attract each other; each experiences an equal but opposite gravitational force.

Weight, Mass, and Gravity

Gravitational Force

The force that attracts all masses, usually noted when one mass is large (e.g., Earth).
Effects:

Objects fall towards the ground.
All objects have weight due to gravity.

Mass vs. Weight

Mass: Amount of matter in an object, constant everywhere in the universe.
Weight: Force acting on an object due to gravity, varies by location.

Weight (W) = Mass (m) × Gravitational Field Strength (g)
For Earth: g = 9.8 ext{ N/kg}
For Moon: g ext{ approximately } 1.6 ext{ N/kg}
Weight is measured in newtons; mass is measured in kilograms.

Resultant Forces and Work Done

Free Body Diagrams

Illustrate all forces acting on an object/system.

Resultant Forces

The single force that represents the combined effect of all acting forces.
Resultant force can be found by adding forces in the same direction and subtracting opposing forces.

Work Done

Work (W) is done when a force acts on an object moving it from one position to another. Energy is transferred, calculated as:
W = F imes s
Where:

W = Work done (Joules)
F = Force applied (N)
s = Distance moved (m)

Work is done against friction, even if energy is wasted as thermal energy.
1 Joule of work is done when a force of 1 Newton moves an object 1 meter.

Calculating Forces and Equilibrium

Scale Drawings

Useful for visualizing and calculating resultant forces.
Draw forces to scale 'tip-to-tail' and measure resultant force.

Equilibrium

An object is in equilibrium if the resultant force is zero.
On scale diagrams, this forms a closed loop (e.g., triangle).

Component Forces

Forces can act at angles; they can be resolved into perpendicular components (e.g., horizontal and vertical).
This simplifies calculations and understanding of how forces interact.

Key Examples

A skydiver experiences weight pulling down and air resistance acting upwards. The resultant force determines their acceleration and motion.
A man on an electric bicycle experiences forces: a driving force of 4 N north and wind resistance of 3 N east. The resultant force can be calculated using scale drawings.

Note