# Impulse vs Sticking plaster

1. Oct 4, 2013

### Fabric

Hello everyone,

I do not need homework-guidance, but having read the COC, I decided this was the best suited place for my question. It's a conceptual-understanding type of question.

I am trying to fully understand some new physics concept, namely momentum and impulse.

ƩF = dmv/dt

I = mv2 - mv1

Now, I read about a woodpecker banging its head against a tree about 20 times a second and about 12000 times a day with an average force of 1200 times the weight of its head. The reason that the woodpecker is capable of doing this, is because the impulse i.e. F*Δt = p2 - p1 is very small when it strikes its beak.

My question:

Can Impulse also explain why it never really hurts when you peel off a sticking plaster very quickly, opposite to when you are slowly peeling it off, i.e. is F*Δt = p2 - p1 < epsilon?

Hope this wasn't too irrelevant and any answer is appreciated. Thank you.

2. Oct 4, 2013

### Staff: Mentor

I think this is more a biological/psychological effect. It hurts in both cases, but if you do it quickly the time where something hurts is shorter, and your nerves cannot do more than send "oh no it hurts here!" even if the force is larger.