Episode 400: Preparation for gravitational fields topic

Main aims
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 potential 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 = mg; 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; kinetic energy; gravitational potential energy close to the Earth’s surface = mgh; conservation of energy; Newton’s laws of motion.

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