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Homework Help: I need help in applying Netwon's law of inertia

  1. Mar 9, 2004 #1
    Ok, I am a high school student who is currently taking Honors Physics. I really enjoy the teacher and what we do in the class, but I just can't seem to apply Newton's First Law of Inertia. I had taken a quiz on it, and I did not do very well. If someone is willing to please help me understand this I would greatly appreciate it.
  2. jcsd
  3. Mar 9, 2004 #2
    Do you have a specific question? The First Law is pretty simple, i.e. things move (or don't move) at a constant rate and direction unless a force acts upon it, but has quite a few consequences. Unless you can narrow down where you're getting confused for us, it'll be hard to help you.

  4. Mar 9, 2004 #3
    I think what I am trying to get at is, I am not sure how to apply to say this question:

    1)The head of a hammer is loose and you wish to tighten it by banging it against the top of a workbench. Why is it better to hold the hammer with the handle down, rather than with the head down. Explain in terms of inertia.

    See the problem is I can not quite apply it. Or for that matter I can not apply inertia to anything. I do not know why I have trouble with that, but that seems to be the main problem for me in physics. Thank you for your time.
  5. Mar 9, 2004 #4
    Okay. Let's say that the hammer is moving rightside-up so that it will contact the bench handle-first. The hammer is really two distinct parts, the handle and the head. The head is usually significantly heavier than the handle. So we got this hammer moving, including the head, and then all-of-a-sudden it hits the bench. Naturally, the handle can't magically pass through the bench, so the handle stops on the spot. Now's the question: What happens to the hammer head? The head is not the handle--they're distinct--so it'll still be moving. Which direction will it be moving? Toward the handle. Now, the head is pretty heavy, so it takes quite a bit of effort to stop it. Additionally, all of its inertia (movement) goes into pushing the head onto the handle, so after the head stops, it'll be snugged up against the handle.

    Now let's consider the other case. Let's say the hammer is moving upside-down and the head contacts the bench first. The bench stops the head (since the head also can't magically pass through the bench), but the handle is still moving. Now, the handle is significantly less massive than the handle, so it's easier to stop. Its inertia is also devoted into pushing the handle into the head, but since the handle is so much easier to stop, it doesn't snug up as much by the time it stops.

    Basically, both cases snug the handle up to the head, but in one, the handle's inertia is used while in the other, the head's inertia is used. So it becomes a question of which has more inertia, the handle or the head?

    Does that help any?

  6. Mar 9, 2004 #5
    Yes thank you very much. That helps a lot. Now all I have to do is just know when to apply it everyday situations. Thanks cookie monster
  7. Mar 9, 2004 #6
    That's an easier question! I'll give you a hint: Whenever something's moving or being moved!

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