How can a bluebottle fly fast into a window without damage?

Bluebottle flies are speedy for their size but it's this small mass that saves them from sustaining too much damage.

Asked by: Chris Kirk, by email

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Bluebottles fly quite fast for their size, but in absolute terms the speed is only around 11km/h – slower than a honeybee and much slower than most birds. But the main thing that protects them from damage is their very low mass. Kinetic energy is equal to half the mass times the velocity squared. For a fly that weighs less than 100mg, this comes to less than half a millijoule of energy. This is the same as the energy an adult man would have at a practically immobile speed of 3mm per second.


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