Question

What is the principle of a sucker?

Answer 1

Why can suckers be hold on walls tightly without falling down to the ground?

Answer 2

When you press on it, you force all the air out. This means that there in now a pressure of 1 atmosphere pressing from the outside.

Answer 3

wow this is quite curious question! How can they suck the blood from animals?

Answer 4

We say "suction cup"... Stan is right; the other part of the answer is that max static friction is equal to mu N, and N is the atmospheric force on the outside of the suction cup.