[RickeyD]

Mythbusters on Head-on Collisions – Greg Laden's Blog

[Polar Bear]

Originally Posted by tuccillo

Consider a wall and two golf carts collide into the wall from either side at 20 MPH. The wall doesn't move. Each cart has the same amount of damage. Now remove the wall and have the carts collide head-on at the same 20 MPH. You will have the same effect. Two cars colliding head-on have twice the energy of one car running into a wall but with the head-on collision you have two cars damaged. One car running into a wall does not have to travel at 40 MPH to experience the same damage as if it had a head-on collision at 20 MPH. Now do you understand?

"same effect"...because you say it is so that makes it so? Pretty big assumption there.

How about this...
Scenario 1 - A wall is moving along at 20 MPH and hits a stationary wall.
Scenario 2 - Two walls are moving toward each other, each going 20 MPH, and collide.

The intensity of the impact for both scenarios is exactly the same? I don't think so. Now do you understand?

Look, I know what you're saying. And I don't disagree with you as much as it might appear. The problem is we're comparing apples and oranges. One has walls with zero energy absorption. Another has vehicles with who-knows-how-much energy absorption. But comparing the two is similar to saying the damage of two vehicles colliding head on is similar to one of them driving off a certain height cliff, or being near an explosion, or something else...again...apples and oranges.

Relative velocity at impact is the velocity that matters in a collision. After that is when you start considering other factors such as energy absorption, energy distribution, etc.

[tuccillo]

the effect will be roughly the same. Of course, the discussion was about something different: whether the damage to a cart having a head-on collision with another cart at 20 MPH was the equivalent of a cart colliding with a wall at 40 MPH. They aren't.

Originally Posted by golfing eagles

Well said. The situation is not equivalent because the brick wall is not moving therefore it's momentum (mass x velocity) is 0. This is directly proportional to the kinetic energy of the object, which determines all kinds of things such as damage and injury. If they don't believe this, there is always the field experiment----run your cart head on into another going 20, and run it into a brick wall at 20. Care to guess which is worse?

[RickeyD]

Mythbusters on Head-on Collisions – Greg Laden's Blog

[tuccillo]

Just so there is no confusion, I am addressing the statement that a cart has to run into a wall at 40 MPH to sustain the same (roughly) damage as if it had a head-on collision with another cart at 20 MPH. This is not true. When two carts at 20 MPH collide, the same amount of energy has to be dissipated as if they both ran into a wall at 20 MPH. The wall will absorb a small amount of the energy but the vast majority will be absorbed by the carts (plus some goes into sound and heat). Twice the energy, twice the number of carts, same damage to each cart, same as if the cart ran into a wall by itself at 20 MPH. Of course, there is a fundamental, and I assumed obvious, assumption that we are talking about a "substantial" wall. One that remains intact after the collision.

I will do the mathematical proof but I am not sure anyone will follow it.

Originally Posted by Polar Bear

"same effect"...because you say it is so that makes it so? Pretty big assumption there.

How about this...
Scenario 1 - A wall is moving along at 20 MPH and hits a stationary wall.
Scenario 2 - Two walls are moving toward each other, each going 20 MPH, and collide.

The intensity of the impact for both scenarios is exactly the same? I don't think so. Now do you understand?

Look, I know what you're saying. And I don't disagree with you as much as it might appear. The problem is we're comparing apples and oranges. One has walls with zero energy absorption. Another has vehicles with who-knows-how-much energy absorption. But comparing the two is similar to saying the damage of two vehicles colliding head on is similar to one of them driving off a certain height cliff, or being near an explosion, or something else...again...apples and oranges. But relative velocity at impact is the velocity that matters in a collision. After that is when you start considering other factors such as energy absorption, energy distribution, etc.

[tuccillo]

You are working from the assumption that a wall has the same mass as a golf cart.

Originally Posted by Polar Bear

"same effect"...because you say it is so that makes it so? Pretty big assumption there.

How about this...
Scenario 1 - A wall is moving along at 20 MPH and hits a stationary wall.
Scenario 2 - Two walls are moving toward each other, each going 20 MPH, and collide.

The intensity of the impact for both scenarios is exactly the same? I don't think so. Now do you understand?

Look, I know what you're saying. And I don't disagree with you as much as it might appear. The problem is we're comparing apples and oranges. One has walls with zero energy absorption. Another has vehicles with who-knows-how-much energy absorption. But comparing the two is similar to saying the damage of two vehicles colliding head on is similar to one of them driving off a certain height cliff, or being near an explosion, or something else...again...apples and oranges.

Relative velocity at impact is the velocity that matters in a collision. After that is when you start considering other factors such as energy absorption, energy distribution, etc.

[RickeyD]

Two old men walk into a bar and start to argue. The first guy throws a punch at 45 mph, hits the second guy square in the chin. First guy breaks his wrist, second guy his jaw. Both go to the VRH and wait 14 hours to see a doc. First guy is a Villager, second guy a Stonecrester. They both get ****ed.

[Allegiance]

All laws of science are suspended in the bubble.

[Arctic Fox]

don't forget that we are dealing with energy here, not momentum

momentum is mass x velocity: m x v

kinetic energy is "half m v squared": 0.5 x m x v x v

[Polar Bear]

Originally Posted by tuccillo

You are working from the assumption that a wall has the same mass as a golf cart.

Not at all. You are working from the assumption that "net damage" proves relative velocity does not matter. Not true.

And I could derive the theory of relativity for you too. But since you wouldn't understand it, I won't post it.

You get the last word. It's been fun.

[RickeyD]

Two retired teachers walk into a bar and start to argue. The first teacher takes a swing at maximum velocity straight to the second teachers belly. Immediately the second teacher kicks his opponent square into his family jewel box. Both see the futility of it all, step up to the bar and have a beer.

[RickeyD]

Originally Posted by Polar Bear

Not at all. You are working from the assumption that "net damage" proves relative velocity does not matter. Not true.



And I could derive the theory of relativity for you too. But since you wouldn't understand it, I won't post it.



You get the last word. It's been fun.

General or Specific, carry on...

[tuccillo]

I tell you what, you go ahead and prove your point, whatever that may be. You can have the last word when you post your proof. Oh, and you can skip the personal insults.

Originally Posted by Polar Bear

Not at all. You are working from the assumption that "net damage" proves relative velocity does not matter. Not true.

And I could derive the theory of relativity for you too. But since you wouldn't understand it, I won't post it.

You get the last word. It's been fun.

[RickeyD]

Mythbusters on Head-on Collisions – Greg Laden's Blog

[chuckinca]

From Wikipedia:

While it is true (via Galilean relativity) that a head-on crash between two vehicles traveling at 50 mph is equivalent to a moving vehicle running into a stationary one at 100 mph, it is clear from basic Newtonian Physics that if the stationary vehicle is replaced with a solid wall or other stationary near-immovable object such as a bridge abutment, then the equivalent collision is one in which the moving vehicle is only traveling at 50 mph.,[3] except for the case of a lighter car colliding with a heavier one.

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