In a purple, blue and brown room, sits a rectangular netted area with a red and white target.

Radar guns measure the speed of a travelling ball in kilometres per hour.

How it works

Throw a ball at a target, so a radar gun in the middle can measure your throwing speed.

Things to try or ask around the exhibit

  • Throw the ball straight at the target and radar gun. How fast was your throw?
  • How does the radar gun detect and calculate the speed of your thrown ball?
  • Where have you seen radar guns being used?


A radar gun is located in the middle of the target. Radar guns send out radio waves of a particular length. These waves hit a moving object such as a car (or in the case of this exhibit, the thrown ball).

The waves bounce back off the ball (or are reflected). The waves are 'squashed' by the moving ball so that the reflected waves have a shorter wavelength. The faster the ball is travelling, the shorter the wavelength of the reflected waves. The new wavelength is measured by the radar gun to calculate the speed.

Finding the science in your world

An object moving faster than the speed of sound pushes air particles into each other, creating a shock wave. This is called a sonic boom and sounds like a huge bang! You’d have to throw a ball faster than the speed of sound (1235 km/h) to make a sonic boom!