The study of Forces is fundamental in Physics, so it is a good place for us to start.
The AQA KS3 Science Specification (so not just a Physics specification) starts with Forces, which is perhaps an indicator of how important a topic it is.
We are going to start with a short Introduction to forces, to cover some details not mentioned in the AQA specification but which are really important.
A good question to start with is:
What is a Force?
And the answer is:
"A force is a push or a pull that acts on one object due to its interaction with some other object."
1) The force between a shopping trolley and a customer when the customer pushes the trolley along the aisle.
2) The force between a strong man and a car when the strong man pulls the car along a road.
3) The force felt between two magnets.
4) The force felt between a ball and the ground (the Earth) which is particularly noticeable when the ball is released from a height above the ground.
For each of the examples mentioned you should be able to identify the 2 objects that are involved and whether the force is a push or a pull.
Can you do it?
What about this example:
A tiny comet is observed in orbit, in the Oort Cloud, perhaps a billion kilometres from an observer on Earth. What force is involved and what are the two objects?
Answer: the force is gravity and the two objects are the comet and our Sun.
The point is: there are always TWO objects involved whenever a force acts, even when the distance between them is so great that it is difficult to identify both objects; and forces are just pushes or pulls!