Force and motion

Introduction

The topic of force and motion involves some quite counter-intuitive ideas. Informal conceptions of force are held by children and adults alike. Force and motion activities provide some rich opportunities for different representational modes: diagrams, graphs and charts, and metaphors to do with human action.

This topic overlaps considerably with other topics in these resource materials, such as 'Air and flight', 'Floating and sinking' and 'Magnetism'

Key concepts of force and motion

The activities in this topic are designed to explore the following key concepts:

Early years

• Forces can be thought of as 'pushes' and 'pulls'.
• Forces can make things move or stop or hold things up or squeeze things.
• Friction is a common force that stops things moving or slows things down.
• Gravity is a force that makes things fall.

Middle years

• Forces cause changes in motion, and are not (unlike momentum and energy) associated with motion itself.
• Forces are our way of describing the way effects such as pushes, pulls or gravity can influence the motion of things.
• A force is an effect on an object, not a property of the object or its motion. It is something that is done to, or acts on, things.
• A change in motion (speeding up, slowing down, swerving) is caused by an external effect and not by the object itself or something inside it.
• Forces occur in action-reaction pairs. Thus if you push on something it will push back on you. Your standing body pushes down on the ground, and the ground pushes back up on you.
• Pairs or sets of forces will add together to affect motion, but the addition must take into account direction. Forces can cancel each other.
• Common forces include contact forces (physical pushes, support or traction from the ground, friction, air or water resistance opposing motion, force from wind) and field forces (gravity, magnetic forces, electric field forces).
• Motion can be described by representing the distance something travels in a time interval.