Scientific explanation of why you can’t catch a dollar bill with two fingers

If someone offers easy to 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 can not catch it in any way. Moreover, not a single person is capable of this. The point is 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 a bill with one hand, and catch it with the fingers of the other hand, because the brain gives a command before the second hand releases the piece of paper. If you try to catch a bill thrown by another person, then nothing will work.

In the latest Numberphile podcast from the Research Institute of Mathematical Sciences (MSRI) , Tadashi Tokieda details this topic .



The signal from the brain to the muscles of the fingers takes about 0.2 s. The question is how far a piece of paper can fly in this time. The distance D is determined by the formula:

D = ½ gt ² ,

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

On the Earth's surface 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.

By measuring a dollar bill, you can easily make sure that its length is 15.5 cm, so that a person will not be able to physically react. Even in the person with the best reaction, the fingers will touch 4 centimeters higher when the bill is already flying down.