please help?

Question

Your empty hand is not hurt when it bangs lightly against a wall. Why is it hurt when it bangs the same wall while carrying a heavy load? What Netwon's law is this?

I need it for my science hw
help is appreciated
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Answer 1

I think it is the second and third laws of motion of Newton. I think that, according to the second law, F=ma, were F=force, m=mass and a=acceleration.

And according to the third law, there is an opposite reaction for every action.

So, your hand bangs with a force against a wall and receives a reaction equal to that force. If you carry a heavy load at the same acceleration, then the force is greater (since we have to add the mass of the load to the mass of your hand), and then the reaction is greater, and thus there are more chances to get hurt.

I guess that is the reason, what do you think?

Answer 2

What happen is that you hit stronger when you carry some heavy load. Apply this Newton law: F = a . m , then

In case of empty hand:

F1 = a1 . m1

F1 is the force that the wall act on your hand weighted m1 when it deaccelerate at a1.

Case of loaded hand:

F2 = a2 . (m1 + m2)

Where m2 is the mass of the load.
The deacceleration results the same in both cases, then a1=a2=a and so:

F2 = a . ( m1 + m2) = a . m1 + a. m2

==> F2 = F1 + a . m2

So the extra force you receive in your hand is depending drectly on the extra load you carry.

Answer 3

The heavy load increases the mass. The force is proportional to the mass (times the acceleration):

F = ma

So the force on the hand is very much greater. This is Newton's Second Law.