How fast are the planets?

Which planet is travelling the fastest in its orbit? Which is slowest? Is there a link between distance from the sun and how fast the planets travel?

Start by asking the students to come up with what information they would need to work this out. You can then take their ideas and if necessary lead them to working out each planet’s speed by doing the distance travelled in it’s orbit (assume circular orbits) and the time taken for one complete orbit (a planetary year).

You can Google the orbit radii and planetary year times in the lesson. Get them to convert the units; if the distance is in km, get them to convert to m; if the planetary year is in earth years, get them to convert to seconds etc. They could even use standard form to work with the large numbers involved.

This idea came from watching Mr S teach a lesson which was based on using pi in real applications. In fact, the task uses many areas of maths including speed = distance / time, units conversion, compound units and standard form.

An engaging using-and-applying investigation for a high-attaining group. Cheers Mr S!

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