Naked Science Forum
General Science => General Science => Topic started by: Alpesh Patel on 19/07/2010 10:30:02
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Alpesh Patel asked the Naked Scientists:
Hi, my name is AL,
I love your shows (http://www.thenakedscientists.com/HTML/podcasts/). Good works guys.
When you watch fire works there is fireball in sky.
But why does it look like it's coming towards us?
Thank you.
AL
What do you think?
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It's an optical illusion. Actually, half of the explosion is moving toward you, and half is moving away (Conservation of momentum).
Normally when something comes towards you the size of the object increases. So there's an assumption that's built into your brain that something rapidly increasing in apparent size must be approaching you.
Most of the time it's true, but with fireworks, half of the firework is moving away from you, but that's not very obvious.
The net upshot is that exploding fireworks always seem to be approaching you, even the bit that's moving away.
The reason your brain assumes this is survival- things that are approaching you rapidly is often a survival threat, better safe than sorry.