## What to expect

In this topic we will consider another form of oscillatory motion: that of objects moving in a circle. For objects moving horizontally or in space, this is usually straightforward to model with the same forces acting throughout. However, vertical circles involve changing sizes of relative forces (and often speed) due to the gravitational force. You will then consider forces that act between masses more generally, and the types of gravitational field.

## Learning objectives

After studying this topic, you should be able to:

- Explain how the radius of a satellite's orbit affects its speed
- Describe how satellites stay in orbit even though they are not powered by anything
- Derive the relationship between gravitational potential energy and position for a non-uniform field

### Circular motion

We have all experienced circular motion!

### Gravitation

A field is a region of space where a force is experienced.

### AHL Gravitational fields

Close to the surface of a large mass (like Earth), the effects of gravitation are uniform. Further out, we realise the the gravitational field of a spherical mass is in fact radial. This has implications for how we calculate forces, field strength, potenti