Active and passive
Teaching Guidance for 14-16
When I act, and when I don't
Wrong Track: I push on the table, and then it pushes back.
Right Lines: Isolating the table, there's a force exerted by you, acting on the table. Isolating you, there's a force exerted by the table, acting on you.
Equal, but symmetrical descriptions
Thinking about the learning
The idea that one thing pushes, and then another pushes back might grow naturally from the suggested introduction to forces in the SPT: Forces topic, where the force exerted by an inanimate object is likened to the actions that you can take to effect changes in the world.
Teacher: You can
pull, and so can other things
Thinking about the teaching
We'd suggest that you develop a
forces acting on object description from the interactions of an object with its environment for each occasion. Newton's third law is useful as you switch focus from one interacting object to another, but it applies to all forces equally.
In some ways that's the whole point of the forces-plus-masses world view. Once you have simplified to forces acting on a mass, then you can find the resultant and predict the motion without further reference to the environment.