Why the balloon does not pop when there are a lot of needles? There is a famous experiment where a balloon pops when we push it against a needle, but it doesn't pop when we push it against a lot of needles.  Why is this?
 A: A link to that experiment will be welcome, but even without it :
If you push the balloon against a needle, this single needle will have to resist to your push on a very small area of the balloon, (its tip, essentially) thus exerting a very high pressure that would burst the skin of the balloon before the general shape of the balloon changes enough to adapt.
If you push it against many needles, the push will be shared and the pressure on each tip will be divided by the number of needles. And if you try to push harder, it will not work so easily, because then the whole balloon will change shape and spread in directions where there are no needles, without exerting much more push on the general area where the set of needles is concentrated.
A: Many needles minimizes pressure, given same pushing force as per :
$$ p= \frac F A = \frac {F}{kA_0} $$
where $A_0$ is needle tip area and $k$ - number of needles. So as number of needles $k$ increases - "pushing pressure" decreases, given same pushing force $F$.
