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Help understanding a physics inertia experiment(Hammer and a heavy block)

by ShizukaSm
Tags: block, experimenthammer, heavy, inertia, physics
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ShizukaSm
#1
Jan10-13, 11:20 AM
P: 85
The experiment is the following:

First part - The demonstrator puts an egg in the table, and places a heavy block resting above the egg, then he applies a force in the heavy block using the hammer, and the egg doesn't break.
Second part - Now he takes the heavy block away, and instead places a lighter wooden block, then applies a force with the hammer again, and breaks the egg.

The explanation to this was "The inertia of the heavy block doesn't allow the egg to break" but I don't really get it. I mean, wouldn't the same force be 'transferred' through the block and act on the egg? The same way if I push one block that touches another, the both will move?

Ps: A similar experiment can be found here, if my explanation was not clear:
http://webapps.lsa.umich.edu/physics...mo.aspx?id=473
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A.T.
#2
Jan10-13, 12:18 PM
P: 3,932
To squeeze the egg you need to accelerate the block. A more massive block will accelerate less, so it will move less in the short time period of the impact. If the force is applied continuously, the it doesn't matter which block you use. But a hammer applies just a short force impulse.
ShizukaSm
#3
Jan10-13, 05:25 PM
P: 85
Sorry but I still don't get it. What do you mean by it will accelerate less? I mean, I believe you, but I don't get it, take a look at my point of view:

IF I apply a force F in a block (Any block, that is) that force would be transmitted to whatever this block is touching (in this particular case, the egg). So, after applying a force F I would have F + Weight acting on the egg, and thus, the heavier the block the easier it would be to break the egg.

I understand that some part of my reasoning must be wrong, but... where?

Studiot
#4
Jan10-13, 05:30 PM
P: 5,462
Help understanding a physics inertia experiment(Hammer and a heavy block)

The hammer doesn't apply a sustained force as AT noted.

It applies what is known as an impulsive force or impulse.

The mechanics of impulse is different from ( and harder than) sustained forces like weight.

http://en.wikipedia.org/wiki/Impulse_(physics)
ShizukaSm
#5
Jan10-13, 07:12 PM
P: 85
Oh, I see, I think I understand a little better now.
Thanks a lot!
russ_watters
#6
Jan10-13, 10:08 PM
Mentor
P: 22,252
In order to transmit the same force, the egg would have to be perfectly rigid. But since the egg will compress a little before breaking, the motion (acceleration) of the block matters. The acceleration essentially absorbs the force.


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