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It has happened many times and i have ignored it everytime. Yesterday it happened again .
I was travelling in a train and saw a fly (insect) flying near my seat.

Train was running at a speed of around of 100 km/hr. So according to the physics rules , my speed will also be 100 km/hr as i am sitting inside the train. But as far as the fly is consider, it is flying inside the train , the speed of the fly is very less as compared to the train. So why does not the fly stuck on the one side of the train ?

As the fly is not in physical contact with the train, will its speed be 120 km/hr?

Qmechanic
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vikiiii
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2 Answers2

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Have a look at http://en.wikipedia.org/wiki/Galilean_invariance. This is not too mathematical and explains what's going on.

The basic idea is that there is no such thing as absolute motion. For example, because the earth is rotating as I sit here typing I'm moving at about 800 miles per hour. Why am I not splattered against my computer screen? It's because everything around me is moving at the same speed, so relative to where I'm sitting I'm not moving.

In the specific case of the fly, the fly moves by beating it's wings against the air. But the air is stationary with respect to you, otherwise you'd be sitting in a 100km/hr wind. That's why you see the fly moving at whatever speed flies normally move at.

John Rennie
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The fly is flying in the air inside the closed train. As this air moves with the train (you don't feel the wind blow), the fly can just fly in the air in your frame of reference. If it is flying with 20 km/h in the train, it is 120 km/hr relative to the earth.

Bernhard
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