#### Chapter 7 - Gravitational Fields

The first of the fields covered in the GCE A Levels is the gravitational field. This video introduces us to the idea of gravitational field lines and discusses some of the features of field theory.

We can study gravitational fields in space quantitatively using Newton’s Gravitational Laws. In the GCE A Levels, we must be able to compute the gravitational field strength at any point in space and this video will discuss this.

In the GCE A Levels, we need to know Newton’s Law of Gravitation, which describes the gravitational force between two masses. This video discusses this concept and how it relates seamlessly to gravitational field strength at a point.

Gravitational potential is similar to gravitational field strengths as they describe what happens at a point in space. In the GCE A Levels, we must understand how to compute the gravitational potential at a point, and also explain why the values are negative. This video will also explore what happens to the potential at a point when multiple masses are involved.

The gravitational potential energy of an object at a point is easily computed if we know the gravitational potential at that point. In the GCE A Levels, we must also understand the concept of equipotential lines. This video will explain this and how we can use equipotential lines to study the energy changes of an object moving around in space.

In the GCE A Levels, we must understand that the gravitational field strength is equal to the negative gravitational potential at a point. This video will discuss this using the concept of equipotential lines, and also mention that the gravitational force on an object is its negative gravitational potential energy gradient.

In the GCE A Levels, you may be asked to plot or interpret graphs of quantities related to gravitational fields or potentials. This video will explain how this is done in detail.

In the GCE A Levels, we have to understand the concept of escape velocity. This video discusses that, including the derivation and the assumptions of the escape velocity expression.

Masses can orbit each other because their gravitational forces produce centripetal forces. In the GCE A Levels, we study the generic binary mass orbit, but we also commonly consider the scenario where one mass is much larger than the other. This video discusses the binary star model, and also discusses the simplified model where a much smaller mass orbits around a relatively stationary larger mass.

For several masses that orbit one central mass, think of our solar system, Kepler’s Third Law showed that the square of their periods is directly proportional to the cube of their orbital radii. While Kepler’s Third Law is not officially in the GCE A Level syllabus, it is still often tested as we know enough to derive it.

Objects in orbit have unique expressions for their gravitational potential energy, kinetic energy and total energy. In the GCE A Levels, we are often required to derive and use these expressions, and so this video will address these.

A special type of orbit we must understand in the GCE A Levels is the geostationary orbit. This video discusses the conditions, advantages and disadvantages of a geostationary orbit.