Which shapes feel heavier?

A cream and purple coloured exhibit table and headboard with the text 'Which shapes feel heavier?'. On the table top sits a divider board with four black cylindrical objects.

The way your hand grips a shape can affect how heavy it feels, even though it's the same mass as another shape being lifted.

How it works

Lift two different sets of shapes or weights. One pair of shapes shows the texture-weight illusion, while the other pair of shapes shows the size-weight illusion.

Things to try or ask around the exhibit

  • If you close your eyes and lift the small and large objects at the same time, the illusion of the smaller object feeling heavier seems to disappear.
  • Have you ever picked up a large box, without realising that it was empty, and almost flung the box into the air?

Background

The size-weight illusion gives you the impression that a smaller object feels heavier than a larger object even though both objects are the same mass. When you prepare to lift something, your vision unconsciously primes your muscles to lift a larger object with more force or tension compared to a smaller object. Because the larger object actually needs less muscle tension than you expected, the larger object feels unexpectedly light. While you’re getting ‘bottom up’ signals from your muscles that the shapes actually weigh the same, you still experience an illusion that the smaller shape is heavier.

With the texture-weight illusion, some people find that a smooth shape feels a little heavier than a textured shape, because they need to use a stronger grip to lift the smooth shape, which gives the illusion that it feels heavier.

Finding the science in your world

You may experience the size-weight illusion when attempting to lift a large box that is lighter than you expect. Your brain probably assumed the box would be heavy, so you primed your muscles to use more force than you actually needed, creating a strange sensation when you lift the box and realise its true weight.