We can bounce objects off each other, and by measuring their velocities before and after the bounce, figure out the ratios of their m's. Pick one object to call the unit mass, and now we have a set of m's.
Now we get to the hard part. What are the F 's? Let's say we see some m with an a. So we must insist on some rules about the F 's. The third law says that there needs to be an opposite F on something else, and we can insist that the something else is fairly nearby. More generally, we can insist that the rules for when there should be an F shouldn't be too weird or complicated. Up to a point, that program works. That's a very compressed version of a long discussion. Feel free to follow up.
It seems like this is what Mr. Newton did while experimenting on accelerating objects before he came up with this law, but since he was the head of the British Royal Society of science, no one dared question him. It doesn't have to take an Einstein to realize that, but a willing to be disattached from prejudices. I hope no one gets offended by my questioning as if I attacked their religious beliefs. Historically speaking, humans held unshakable beliefs as facts for hundreds of years before they finally tossed them out as falsehoods, and I believe that there are still lots of falsehoods that will be tossed out of science facts in the future.
Thank you. In physics, force is the thing defined as the product of mass a scalar and the acceleration vector of that mass.
This means the more mass an object has, the more force you need to accelerate it. For a constant mass, force equals mass times acceleration. F is force, m is mass and a is acceleration. Thank you. Isaac Newton's First Law of Motion states, "A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.
That situation is described by Newton's Second Law of Motion. For a constant mass, force equals mass times acceleration. F is force, m is mass and a is acceleration. The math behind this is quite simple.
If you double the force, you double the acceleration, but if you double the mass, you cut the acceleration in half.
Newton expanded upon the earlier work of Galileo Galilei , who developed the first accurate laws of motion for masses, according to Greg Bothun, a physics professor at the University of Oregon. Human beings can see and manipulate the position and velocity of everyday objects quite well; much, much better than they can see the acceleration.
People routinely get the sign! Indeed, I suspect it is possible to in some sense deduce the second law of motion from thermodynamics. Cf the work by Ted Jacobson on the Einstein field equations as equations of state , and more recent followups. And so on — a panoply of great questions! It takes as given a lot of pre-existing intellectual structure. I assume you have a basic comfort with differential equations, with test particles, with gravitating bodies, with acceleration, and so on.
And then we leave most of it fixed, and poke hard in a few places, seeing what happens when you change those things around, but leave most of the intellectual edifice unchanged. The notion of universal force laws is one of the most beautiful and audacious ideas humans have ever developed. Perhaps one approach could be to write a piece of discovery fiction explaining how the second law could have come to be discovered. I find it truly remarkable just how much Newton and his contemporaries needed to get right.
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