Question

Why does a gymnast rub powder on his hands before exercising on a set of parallel bars? (I need a scientific answer)

Answer 1

So he doesnt slip. Gives himself a good grip. The powder and the bar have friction. More friction = better grip

Answer 2

Answer

To increase friction for a better grip.

Answer

Most human beings do sweat hands especially on the palm. When this happens the person will not have a good grip of heavy objects because they will slide/slip from the hand.

By applying the powder, you are trying to make the hand dry hence increasing the friction for a better grip.

If the gymnast doesn't do this the parallel bars may slip from the hands and injure himself or herself.