If fleas were the size of dogs could they jump over the moon? No, says Hannah Fry, the strength of animals varies with size, and explains everything from fleas to Usain Bolt.

Have you ever heard the claim that if a flea was the size of a dog it could jump over the moon? Well it isn’t possible; the flea’s exoskeleton would explode on impact.

To explain why, Hannah Fry looks at the science behind how the strength of animals changes with size, and how this explains why sprinters like Usain Bolt have the body shape they do.

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