TOPIC 1 - Types of forces and resultant forces

Equation linking force, mass and acceleration

Force = mass x acceleration
(F = ma)

Definition of a force

A force is a push or pull.
- There are 9 types of forces:

Gravity or weight

A force that acts straight downwards towards earth's center.

Reaction force

Acts perpendicular to a surface and away from it.

Electrostatic force

The force between two charged objects. The direction depends on the type of charge (like charges repel, opposite attract.)

Thrust

A reaction force (push or pull)

Upthrust

The upwards force of any object in fluid.

Drag, air resistance or friction

A force that slows down an object in motion.

Lift

A force that is perpendicular to the oncoming flow direction.

Tension

A force that stretches an object.

Compression

Forces that squeeze an object.

Why is force a vector quantity?

Force has both magnitude and direction.

Definition of friction

Friction is a force that opposes motion.

Describe the effects of forces between bodies (3)

- Changes in SPEED: forces can cause a body in motion to speed up or slow down.
- Changes in DIRECTION: forces can cause bodies to change their direction of travel.
- Changes in SHAPE: forces can cause bodies to stretch, compress, or deform.

Friction: Static friction

Friction between solid surfaces which are gripping.

Friction: Sliding friction

Friction between solid surfaces which are sliding past each other.

Friction: Resistance or drag

Occurs in liquids and gases.

Balanced force

Equal forces acting on an object in opposite directions (eg. equal amount of weight and upthrust)

Unbalanced force

The force applied in one direction is greater than the force applied in the opposite direction.

Definition of resultant force

A resultant force is the combined action of all the forces acting on an object.

Calculating resultant forces: Forces working in opposite directions

Subtracted from each other.

Calculating resultant forces: Forces working in the same direction

Added together.

Resultant force worked example: Calculated the magnitude and direction of the resultant force

Step 1: Add up all of the forces directed to the right

4 N + 8 N = 12 N

Step 2: Subtract the forces on the right from the forces on the left

14 N - 12 N = 2 N

Step 3: Evaluate the direction of the resultant force
The force to the left is greater than the force to the right therefore the resultant force is directed to the left


Step 4: State the magnitude and direction of the resultant force

The resultant force is 2 N to the left