# The concept of force

As another abstract concept it is vital to get your students to see that forces are understood by the changes that they initiate. They need to learn that we classify forces as either contact forces or action at a distance forces.

Use this video to get fired up to teach the topic. The box demonstration is the best starter for your first lesson. Use it to get your students thinking about forces in the most general context before you focus on specific aspects of the topic. Gravity (an action at a distance force) gives the box its weight, in contact with the table the normal reaction (a contact force) balances weight so there is no resultant force and therefore there is no change in motion, but the box hanging over the table pulled up by the helium balloon gives plenty to discuss. The ideas involved link back to ideas in the kinetic theory list.

Simplifying a situation such as a ladder leaning against a wall as a free body diagram is at first a challenge, but with practice your students will learn the power of the strategy. By using vectors to represent forces they can evaluate the effect of these forces. If these forces lead to a resultant force there will be a change in motion. If the forces are balanced then there will be no change in motion, but there could be a change in shape! In analysing examples they will be covering math skills that practise using angular measure and visualising 2D and 3D representations.

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