You may also like

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?

Hold Still Please

Age 16 to 18
Challenge Level

Don't forget that the total vector force on a particle equals the vector sum of the forces from all other particles.

For an unconstrained particle not to move, the total force on the particle must equal the zero vector.