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Q & A: Brownian motion

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Most recent answer: 09/11/2014
Q:
In the Brownian motion experiment using a smoke cell..The smoke molecules are struck on all sides by air particles with the same speed why do the smoke particles not stay still?
- Tara (age 14)
UK
A:

Nice question.

On average, the particle is hit as much from one side as another. That means that on average it won't head on direction or another. That's only on average, however. Just by random chance, any particle will be hit a bit mre from one direction or another. So it will jitter around in unpredictable directions.

Despite the randomness of the motions of individual particles, you can predict very accurately how rapidly a cloud of these particles will spread out.That's a funny thing about pure chance processes like coin flips. They can be very predictable in some ways.

Mike W.


(published on 09/11/2014)

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