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Lunar Leaper

Gravity on the Moon is about 1/6th that on the Earth. A pole-vaulter 2 metres tall can clear a 5 metres pole on the Earth. How high a pole could he clear on the Moon?

Which Twin Is Older?

A simplified account of special relativity and the twins paradox.


A ball whooshes down a slide and hits another ball which flies off the slide horizontally as a projectile. How far does it go?

Escape from Planet Earth

Age 16 to 18
Challenge Level

At what distance from the earth would an object have zero gravitational potential energy?

How fast would the balls need to be thrown so that they only just reach this point?