The Speed of Planets


In this activity pupils are shown how to calculate the speed that planets move through space, by using a planetary database.

Resources required

Table of planetary data; calculator.

Content

  1. Pupils should be aware that speed = distance x time. A short discussion of this, perhaps with a formula triangle, may be useful.
  2. The distance of each planet from the Sun is given in metres, expressed in standard index form. Pupils should use this to calculate the actual distance the planet travels during the course of a single orbit and express this in kilometres.
  3. The sidereal period is the time taken by a planet to execute a single orbit around the Sun. These times are given in different units; they should be converted to hours or seconds.
  4. The speed of each planet (and of the Moon) can be calculated from the above information in km/h or km/s. Put the results in a table and plot a graph of speed against distance from the Sun.
  5. Which is the fastest planet? Which the slowest? Does there appear to be any pattern in the data or in your graph?
  6. What factors could distort the results in this experiment?

Keywords

Circle, π, distance, time, speed

Teachers' Notes

  1. These calculations assume that the orbits of the planets are circular, which is not the case; the speed that results from this experiment is an average, estimated speed.
  2. Pupils need to be aware that 1 km = 1000 m and that 1 day = 24 hours
  3. If the speeds are to be given in metres per second instead, then pupils need to know that one day = 86 400 seconds, or they need to be able to work this out.
  4. Clearly some knowledge of standard index form is desirable here.
  5. The abscissa of the graph should have distance as a multiple of the Earth's distance from the Sun (known as 1 Astronomical Unit).
  6. Pupils can search for their planetary data using the solar system section of this website, and this exercise can be useful in covering ICT elements of Mathematics.

For more details describing pupil activities associated with determining the speed of planets click here.

The National Schools' Observatory wishes to thank
Carl Sanderson for writing this page of the Staffroom.

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