You have a vehicle (a car, let's say) which we'll refer to with the subscript v
You have an old tin can, which we'll refer to with the subscript c
You connect the vehicle and the can with a length of inelastic fishing line (technically there is no such thing, but Power Protm 60lb braided line comes damn close.)
And the vehicle accelerates, towing the can that's on the line. Here we'll assume perfect conditions, and the can just slides rather than bouncing around.
Newton's third law tells us that "action and reaction are opposite and equal", so the vehicle's motive force (its traction against the road) must be opposite and equal to the can's resistive force (its friction sliding along the road).
fv=-fc . So far so good, and we're all on the same song sheet, right? RIGHT??
Now, force=mass*acceleration as we all know, so:
(ma)v = -(ma)c
But the vehicle and can are connected by an inelastic line, so the acceleration values are identical by definition, so we can cancel the acceleration from both sides of the equation, leaving:
mv = -mc
Here we have proven that the vehicle and the can are the same but opposite mass. 1500kg of car and -1500kg of can? Or 16gm of car and -16gm of can? Or the reverse polarity (as it were), of course.
QED
Either way, you don't want those buggers to get into close proximity or your experiment just got blown to poop. Beats me how anything ever moves, what with ol' Isaac and his 3rd law. Wonder if he knew what horrors he invented there?
You have an old tin can, which we'll refer to with the subscript c
You connect the vehicle and the can with a length of inelastic fishing line (technically there is no such thing, but Power Protm 60lb braided line comes damn close.)
And the vehicle accelerates, towing the can that's on the line. Here we'll assume perfect conditions, and the can just slides rather than bouncing around.
Newton's third law tells us that "action and reaction are opposite and equal", so the vehicle's motive force (its traction against the road) must be opposite and equal to the can's resistive force (its friction sliding along the road).
fv=-fc . So far so good, and we're all on the same song sheet, right? RIGHT??
Now, force=mass*acceleration as we all know, so:
(ma)v = -(ma)c
But the vehicle and can are connected by an inelastic line, so the acceleration values are identical by definition, so we can cancel the acceleration from both sides of the equation, leaving:
mv = -mc
Here we have proven that the vehicle and the can are the same but opposite mass. 1500kg of car and -1500kg of can? Or 16gm of car and -16gm of can? Or the reverse polarity (as it were), of course.
QED
Either way, you don't want those buggers to get into close proximity or your experiment just got blown to poop. Beats me how anything ever moves, what with ol' Isaac and his 3rd law. Wonder if he knew what horrors he invented there?
via International Skeptics Forum http://ift.tt/1M05EHk
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