Marble-ous Ellipses – Speed and time of orbiting bodies

Brief description:

In this activity, students will use an elliptical board to obtain speed and distance measurements for an object in an elliptical orbit.

The results are then plotted on a graph of speed against time in order to understand how gravity effects (or changes) the speed of a planet or a satellite in an elliptical orbit.

It is recommended that students have background knowledge in the concepts of kinetic energy and gravitational potential energy, as well as the concept of velocity vector before beginning this activity.

Subject:
Science, Physics, Mathematics
Learning Objectives:

  • Students should be able to construct a graph of speed against time and link this to ideas of acceleration and distance to understand the principles of orbital mechanics.
  • Students should understand how the strength of gravity varies with distance from a planet or star.
  • Students should relate this to how a planet or satellite accelerates and decelerates in an elliptical orbit.

Age range:
14 – 16 years old

Time
Preparation: 1 hour
Lesson: 15 minutes to 1 hour

Resource available in:
 English, French, Italian, Portuguese, Spanish, and Estonian.
Download activity - EN
Activity 1: Measuring speed and distance on an elliptical board

In this activity, students will use an elliptical board to obtain speed and distance measurements for an object in an elliptical orbit.

The results are then plotted on a graph of speed against time in order to understand how gravity affects (or changes) the speed of a satellite in an elliptical orbit.

Students are then asked a series of questions on the graphs produced during the activity, and a discussion on comet observations and explanations finishes the actvitity.
Equipment

  • Ellipse board – made in advance, for instructions see Appendix: Elliptical board template instructions
  • About 75 small marbles (a few small ones are useful to fill in the sharp end of the wedge)
  • 2 x metre rulers or rods
  • 50 cm of string
  • Non-permanent marker

Did you know?

For thousands of years, philosophers and astronomers argued about the nature of the structure of the Solar System and beyond.

Two conflicting models for our Solar System emerged: geocentric (or Earthcentred) and heliocentric (or Sun-centred). Around 200 BC, the ancient Greek astronomer Aristotle was a supporter of the geocentric model and proposed that the planets (and the Sun) moved at uniform speeds along circular paths around the Earth, which was at the centre of the Universe.

We know now that this model does not fit with observations of the universe, and instead the heliocentric model has been accepted.

Illustration of the geometric model - the belief that the Earth lies at the centre of the universe

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