Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Sir Isaac spoke, and there were light. But why, really?

  1. Jun 22, 2004 #1
    Some vise guy once stated that "a body in uniform motion stays in uniform motion, if no force is acting on it, a body at rest stays at rest if no force is acting on it."

    Sure, our universe works this way, I think we all agree on that... but why does it work like this? Does anyone know?

    As far as I know, not relativity nor quantum mechanics or string theory violate this principe (allthough I know little of relativity and extremely little of quantum mechanics and string theory). Is that correct?

    Cheers fellows.
  2. jcsd
  3. Jun 22, 2004 #2
    How could it not work like that? I think of it as part fact, part definition. If there is an action then there MUSt be a cause. No cause (force) no action (movement)
  4. Jun 22, 2004 #3
    yes but we explain staying stuck to the ground with gravity whereas u just thought of it as fact a few centuries ago. For full definition of our srroundings we need to question why. But it seems beyond everyone to explain why forces are.
  5. Jun 22, 2004 #4
    Oh, so this is philosophy, well perhaps then...

    Should we simply negate the reason to have forces simply because we can not imagine a world without them?
  6. Jun 23, 2004 #5
    Newton's laws of motion are over-simplifications of a more subtle situation described by Einstein. In Relativity, motion and the lack of motion just depend upon your point of view. That is why a body in motion seems to maintain it's velocity and direction unless something else changes it, because for all we know it is we who are moving rather than the object we are observing.
  7. Jun 24, 2004 #6
    ok. thanks.
  8. Jun 24, 2004 #7
    Yer welcome.
  9. Jul 5, 2004 #8
    This is precisely what pre-Newtonian physicists said. They believed essentially the same thing as Newton except had it reversed, and as we all know they were wrong. They thought that the natural position of an object was at "rest" until a force acted upon it. This seems completely in line with common sense (and in fact with what you stated in your post). You throw a rock, your force (cause) guides it through the air but it always inevitably attempts to come back to its natural state, which is resting on the ground. Newton suggested the opposite, you throw a rock, it will continue indefinitely in motion unless another force acts upon it. Essentially Newton was able to transcend Earthly experience and think outside the box. Newton's laws of motion, though they seem fairly simple to us moderns, were actually extremely counter-intuitive.

    My point in all of this is that Newton's laws aren't as obvious as you seem to imply. The "obvious" would end up being the opposite of what Newton discovered. The key in all of this, of course, is gravity which wasn't really viewed as a force until Newton.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook