The scientific explanation of why you can not catch a dollar bill with two fingers

If someone offers to easily earn $ 20 in a simple game - just grab a falling bill with two fingers, in no case do not agree, this is a trap !

The bill falls between your fingers, and you just can not catch it. Moreover, no man is capable of it. It’s a biological limitation: for most people, the reaction time is about 0.2 s .

The trick is that a person can easily demonstrate the trick himself: throw the bill with one hand and catch the fingers of the other hand, because the brain gives the command before the other hand releases the piece of paper. If you try to catch the bill, thrown by another person, then nothing happens.
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In the latest podcast Numberphile from the Research Institute of Mathematical Sciences (MSRI) , Tadashi Tokieda reveals this topic in detail .



The signal from the brain to the muscles of the fingers is about 0.2 seconds. The question is how much distance a piece of paper has time to fly by. Distance D is determined by the formula:

D = ½ gt ² ,

where t is time, g is the acceleration of gravity.

On the surface of the Earth at a latitude of 45.5 ° at sea level, g is, as is known, 9.8 m / s ² .

If we substitute these values ​​in the formula, we get the following:

D = 0.5 * 9.8 * 0.2 ² = 0.196 m,

that is, a little less than 20 centimeters.

Measuring a dollar bill, you can easily make sure that its length is 15.5 cm, so that a person cannot physically react. Even in the person with the best response, the fingers touch 4 centimeters higher when the bill has already flown down.