Professor Tadashi Tokieda from Cambridge University, He explains why it is impossible to catch someone a bill of $ 20 in free fall with his fingers.

Initially there is a biological limit: The majority of people are reacted at about 0,2 seconds. This is the time that it takes to transfer the command from the brain in their hands to catch the greenback.

If you add to the equation the velocity of an object in free fall, we see that it is possible to catch the bill only if it has fallen from a distance greater than 20 cm. However, this is impossible, as the bill has a length of only 15,5/100.