Mass
Forces and Motion

Impossible Tower

Enrichment Activity for 5-11 11-14

What you need

  • About 15 identical flat blocks or books
  • A flat surface

Instructions

  1. Stack the blocks to make a tall column with each placed exactly over the one beneath. Move the top block to the right as far as it will go without falling
  2. Move the top two blocks together so that they overhang the third block as far as possible without falling. Keep going in the same way down the column

Results and Explanation

Your stack seems to defy gravity! You have to shift the blocks by tiny amounts towards the end, so it’s extremely difficult to build from the bottom up.

When you balance the first block, its centre of mass is at the edge of the block below. Each time you balance a new block plus all those above it, you’re judging the centre of mass of this new set.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.

2023 IOP Awards

Teachers of Physics Awards

Recognising and celebrating outstanding contributions to the field of physics education.

Learn more