Force required to destroy identical objects....

[KalStark]

...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...

 

[phinds]

...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.

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.

 

[Drakkith]

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.

 

[KalStark]

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

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.

destructive device is launched/thrown at it.
Is that better?

 

[KalStark]

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 on 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.

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?

 

[phinds]

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?

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.

 

[KalStark]

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.

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?

 

[Drakkith]

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?

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.

 

[KalStark]

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.

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?

 

[Drakkith]

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?

The simple answer is yes. Obviously real life is rarely simple.

 

[phinds]

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?

See Drakkith's post #3

 

[abdullahi abass]

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.

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.)

 

[phinds]

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.)

I think you need to re-read the original problem statement, and perhaps Drakkith's post #3

 

[USeptim]

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 :).