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physwizard
#19
Jan6-12, 12:33 PM
P: 153
Quote Quote by Simon Bridge View Post
You cannot prove the force law ... it the definition of what the Newton means when he uses the word "force". "Force" is defined to be a shorthand word for "the rate of change of momentum".

You are correct that you have to use the force law to determine the force due to the falling weight. Thus the experiment has set up a circular argument.

The best this shows is that falling motion will couple to horizontal motion in a manner consistent with newton's law. So the rules are internally consistent.

What you are seeing is a very common mistake in junior physics classes.

You could also use a newton-meter to drag an object and record the force you use and the acceleration you produced ... no falling weight and you measure force directly... but wait: a Newton-meter actually measures the extension of a spring, converting to force by Hook's Law. The calibration is done by using the 2nd Law, so once again.

I'm sure you can think of others.
thats right. its not really a law, it is the definition of 'force'