1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Force required to destroy identical objects....

  1. Jul 12, 2015 #1
    ...moving at different velocities?
    Hi, i'm a college student who has just taken an interest in Physics and I was up all night yesterday thinking about this. Suppose you have two identical rock, boulder, mountain or whatever sized objects but one is moving at a extremely high velocity while the other is stationary. Would it take more energy to destroy that object given it's speed, or, since both objects are identical, would it not matter? I know it would take more energy/force to change the direction and velocity of the moving object but what about outright obliterating it?? And these are external forces btw...like a grenade or something like that....
     
  2. jcsd
  3. Jul 12, 2015 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    This is a meaningless statement since all motion is relative and you have not specified a frame of reference for either one, plus the fact that you could, for example, specify a frame of reference in which one of the objects is at rest OR you could choose a frame of reference in which the other object is at rest.
     
  4. Jul 12, 2015 #3

    Drakkith

    User Avatar

    Staff: Mentor

    The amount of energy required to destroy something does not depend on the objects velocity. This is a result of the fact that an object moving at a high velocity in one frame of reference can be moving at a completely different velocity in another frame of reference. In its own frame of reference it is stationary.
     
    Last edited by a moderator: Jul 19, 2015
  5. Jul 12, 2015 #4
    Ok, something like....a grenade, bomb, or any destructive device is set to explode when an object moving towards it from....1000 miles away at...20,000 mph.....gets within an inch of reaching it. For the stationary object, that same
    destructive device is launched/thrown at it.
    Is that better?
     
  6. Jul 12, 2015 #5
    So, i'm just trying to wrap my head around this, say a spaceship is moving at near the speed of light. That spaceship would still be affected by missiles the same as any other ship?
     
  7. Jul 12, 2015 #6

    phinds

    User Avatar
    Gold Member
    2016 Award

    You're not getting it. YOU, right now as you read this, are moving at near the speed of light. It's all a matter of what frame of reference you choose. I have chosen a frame of reference in which an "accelerated" particle at CERN is at rest and you are moving at near the speed of light.
     
  8. Jul 12, 2015 #7
    Nah, I guess not. At least not yet. Are you saying that since everything can be put in a different frame of reference, speed is basically a non-factor as far as my question goes -- i.e the energy required to destroy the objects is the same???
     
  9. Jul 12, 2015 #8

    Drakkith

    User Avatar

    Staff: Mentor

    The fact that the closing velocity between the missile and the ship is very, very high will make the damage MUCH more severe, but that's only because there is much more energy in the collision. For any given amount of damage done, the energy is always equal, regardless of whether the energy comes from an explosion, collision, etc.
     
  10. Jul 12, 2015 #9
    So, the missile will still affect the ship same as any other but because of it's speed the damage it takes will be much higher?
     
  11. Jul 13, 2015 #10

    Drakkith

    User Avatar

    Staff: Mentor

    The simple answer is yes. Obviously real life is rarely simple. :wink:
     
  12. Jul 13, 2015 #11

    phinds

    User Avatar
    Gold Member
    2016 Award

    See Drakkith's post #3
     
  13. Jul 19, 2015 #12
    I believe this statement is an unnecessary complication. Once the observer states that the objects move at different velocities.(with respect to a single reference frame: the observer's) Say a difference of 50m/s, this difference in their velocities would be constant, no matter the reference frame (unless we start considering near speed of light, which again, is unnecessary.)
     
  14. Jul 19, 2015 #13

    phinds

    User Avatar
    Gold Member
    2016 Award

    I think you need to re-read the original problem statement, and perhaps Drakkith's post #3
     
  15. Jul 20, 2015 #14
    A collision between two objects, let's name them A and B, will depend on their relative velocities, in fact it will depend on their relative speeds. This relative speed is the speed measured for B in A's inertial frame or the speed measured for A in B's intertial frame, which is the same.

    The greater relative speed, the stronger impact, of course you would have to measure this relative speed just before the collision and you would have to take into account also the orientation (for example, in a car crash, a lateral impact is usually worse than a frontal impact) and probably other facts.

    Hope it helps :).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Force required to destroy identical objects....
  1. Forces in objects (Replies: 4)

Loading...