Forces 09 November 2018 Objectives: To describe the forces between two objects in a range of situations. To represent forces with force arrows.

Starter (10 mins) Give the students pairs of bar magnets and ask them to describe what happens when the different ends are pushed together. They must write descriptions using key words ‘push’ and ‘pull’ and note that the effects happen even when the magnets do not touch.

What are forces?

Push and pull

Types of forces All forces involve interactions between objects. There are several different types. Gravity and magnetism are forces that can act over distances. Friction and upthrust are forces that involve direct contact between objects. Teacher notes Forces during take off include gravity, thrust and air resistance (friction). Photo credit: NASA Marshall Space Flight Center (NASA-MSFC) All types of forces can occur whether objects are still or moving. What forces are acting during this rocket launch?

The students explore a range of forces to show their effects including, magnetic forces, frictional forces slowing an object, frictional forces preventing movement, forces stretching an elastic band, electrostatic forces picking up small piece of paper etc. The can also carry out the Practical and Investigation ‘Push me, pull you’ to explore forces in more depth.

Move on to the representation of forces using plenty of examples, including P2.3 in the Student’s Book and the worksheet ‘Force diagrams’. Students then use forcemeters to measure a range of forces, carefully selecting appropriate meters. They should also measure some compressive forces using a set of bathroom scales (with a newton scale).

Plenary Different groups of students should compare their measurements of forces in different situations to establish the reliability of their measurements and discuss the possible causes of differences. Structured Questions, ‘Forces’, question 1 can be used as a summary task.