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Science

Gravitational Fields

Overview

Students explore gravity as a field force, discovering Newton's universal law and applying it to explain the motion of planets, moons, and satellites.

Learning Objective
Students understand the concept of a gravitational field, can apply Newton's law of universal gravitation, and can explain orbital motion.

Resources needed

  • None

Lesson stages

0 / 7 done
  1. 1 Recap: all masses attract each other. The force is gravity. But how does it work across empty space?
  2. 2 Introduce the gravitational field: every mass creates a field in the space around it. Other masses in that field experience a force.
  3. 3 Field lines point toward the mass that creates the field (unlike electric fields which can point away).
  4. 4 State Newton's law of universal gravitation: the force between two masses is proportional to the product of the masses and inversely proportional to the square of the distance between them.
  5. 5 Apply: the force between Earth and the Moon. If the distance doubled, the force would be one quarter (inverse square).
  6. 6 Explain orbital motion: a satellite or planet moves in a circular orbit because gravity provides the centripetal force. It is constantly falling toward Earth but its horizontal speed keeps it moving around.
  7. 7 Discuss: how do geostationary satellites differ from low Earth orbit satellites?

Tap a step to mark it as done.

Variations

  • Calculate the gravitational force between Earth and the Moon using Newton's law.
  • Discuss how the inverse square law explains why gravity is strong near a planet but negligible far away.
  • Introduce gravitational potential energy and how it changes with height.
More information

Teach: gravitational field, field line, inverse square law, orbit, centripetal force, satellite, geostationary. The concept that orbiting is really continuous free-fall is counterintuitive but essential for understanding satellite motion.

Focus on Newton's law and the inverse square relationship before introducing orbital motion and satellites.

Can students state Newton's law of gravitation and predict how force changes with distance? Can they explain why a satellite in orbit does not need a constant thrust to stay in orbit?

No resources needed. All calculations require only arithmetic. Draw field line diagrams in soil.

Students often think satellites need constant thrust to stay in orbit, like a car needs an engine to keep moving. In orbit, gravity provides the centripetal force — no thrust is needed to maintain speed (only to change orbit).

Gravitational field theory underpins all of astronomy, satellite technology, space exploration, and general relativity. Understanding it provides the conceptual basis for everything from GPS to black holes.

Activity details
Secondary Challenging 25 minutes no prep Whole Class, Small Group Indoor & Outdoor
Topics
Gravitational Fields Newton's Law Of Gravitation Orbital Motion