Year 7 Science

Forces

What is a Force?A force is a push or a pull.Different types of forces can act

on a object at the same time.Forces can act in different

directions.An object can change speed or

direction only when the forces acting on it are unbalanced.

Action forces in one direction cause reaction forces in the other direction.

Different types of forces can act on an object at the same time and in different directions…

• Objects speed up/slow down when the forces are balanced or unbalanced?

ForcesA force cannot be seen! It has no

shape, colour or smellThey are interactions between

objectsThe effects of forces can be seen

If an object is speeding up, slowing down or changing direction there are unbalanced forces acting on it!

Sir Isaac Newton (1642-1727)

Millions saw the apple fall, but Newton asked why.

Measuring Forces

The units of force: the Newton (N)

1N is the equivalent of 98g weight

Or 1kg is 9.8N

ForcesForces

Represented by vectors (drawn as arrows)

This is a vector of size 20N to the 20N right

20N 20N to the left

5N 5N up

Forces

ForcesForces acting Resultant Force

20N

30N50N

20NNo resultant forceBALANCED forces

20N

60N 50N10N

This means that while forces are acting, they effectively ‘cancel’ each other out

Everyday ForcesWhat is a force?

◦A force is a push or a pull.Can you name any forces?

Gravitational

Friction Thrust DRAGMagnetic

Electrostatic

What forces are present?

Contact and Non-Contact Forces

Some forces are touching or contact forces.◦Physical push/pull◦Wind (air)◦Bouyancy (water)◦Friction

Some forces do not make contact and are non-contact forces.◦Gravitational forces◦Electrostatic forces◦Magnetic forces