Activities for Freefall

The slinky and the astronaut spine

A slinky on earth is compared to a slinky in freefall.
The comparison shows us a bit about astronaut spines.


An astronaut in the space station and a scientist on the ground each possess a slinky.

To Do and Notice

The bottom of each slinky is held in one hand the top is held in the other hand.

The slinky is oriented vertically. (In the frame of the camera.)

The scientist releases the top of the slinky, it remains compressed in his hand.

The scientist inverts the slinky, one end falls to the ground.

the audience is asked what will happen when the astronaut releases the top of his slinky.

The astronaut releases the top of his slinky. The slinky expands a little.

The astronaut inverts his slinky, it remains stretched just as before.

The scientist holds the slinky horizontal and compressed between his two hands like an accordion and releases it. It falls to the ground and expands while it is in freefall to the same length as the slinky in the space station.

What's Going On?

On the earth gravity pulls down on the slinks of the slinky compressing them into the hand of the scientist. When the slinky is inverted gravity stretches the slinks down toward the ground.

In freefall the slinky and the hand are falling together. There is no compression of the slinky between gravity down and the hand up so the slinky assumes its natural uncompressed length.

So What?

Astronaut spines are like slinkies.

On earth they are compressed by gravity pulling down on the head and the spine itself. In space they expand. This makes fitting space suits difficult.

Astronaut stories. How much did you grow?

Scientific Explorations by Paul Doherty

© 2000 The Exploratorium

21 November 2000