## Episode 400: Preparation for gravitational fields topic

Teaching Guidance for 16-19

- Level Advanced

In this topic, students will extend their terrestrial experience to develop a much broader picture of the force of gravity, and its representation in the form of a gravitational field.

#### Main aims of this topic

Students will:

- understand the concept of a field and its depiction with field lines
- understand and use Newton’s law of universal gravitation
- understand what is meant by an
*inverse square law* - understand and use the term
*field strength* - understand and use the terms
*energy*and*potential*and know that the zero of potential is defined to be at infinity - understand that the gradient of potential is related to field strength
- understand the motion of objects in gravitational fields (circular orbits only, including geosynchronous orbits)

#### Prior knowledge

Students will have a vague notion of the concept of a field, and is representation by lines of force, from studies of magnetism. When developing the idea of a gravitational field, you can refer back to these earlier ideas.

In earlier studies, your students should have covered the following concepts:

mass; weight *W* = *m**g*
; *g* defined as field strength in N kg^{-1} or as gravitational acceleration in m s^{-2}; all bodies in free-fall (no resistive forces) accelerate at the same rate; work; energy; energy in the gravitational store close to the Earth’s surface = *m**g**h*
; conservation of energy; Newton’s laws of motion.

In their advanced studies, they should also have covered circular motion and centripetal force.

#### Where this leads

The concept of a field is hugely important in physics (traditionally as a model to explain action-at-a-distance

effects). In classical physics the known forces (gravitation and electromagnetism) were modelled incredibly successfully as fields, with a great many applications to industry and society as a whole.

More recently, QED (quantum electrodynamics), often quoted as the most accurately tested theory known to man, is in essence nothing more than a theory about electric fields. Although the modern view of a field is quite different to the classical one, fields are an essential cornerstone of physics.

Gravitation is a great starting point for the subject of fields, introducing and developing concepts that are found in all field physics (such as field strength and potential), and it also gives an opportunity for revising Circular Motion and Energy.