Impact Velocities

[JayKay]

Mod note: Moved from this thread in General Discussion.

... now stuff is flying past me at insane speeds, also my old space station actually came close enough that it loaded but shot past to quickly to even see it

What's insane about 10,000 mph?

Edited October 20, 2014 by technicalfool

[Epthelyn]

What's insane about 10,000 mph?

About 5km/s, or ~11000mph.

[tater]

BTW, at around 3 km/s objects have more energy than their mass in TNT, and it goes up from there, obviously. Let's hear it for v^2.

[Taki117]

About 5km/s, or ~11000mph.

Actually it would be about twice that since both objects are travelling at about 5km/s, meaning that their total speed at rendezvous is about 10km/s or about 22,369MPH

[JayKay]

Actually it would be about twice that since both objects are travelling at about 5km/s, meaning that their total speed at rendezvous is about 10km/s or about 22,369MPH

Well, since we are getting technical, orbital speed on Kerbin is around 2200 m/s at 80 km, but varies depending on altitude and eccentricity. Twice that to account for orbiting in opposite directions is 4400 m/s which is 9842.519685039 mph (give or take.) By comparison, Earth orbit is around 18,000 mph.

[technicalfool]

Actually it would be about twice that since both objects are travelling at about 5km/s, meaning that their total speed at rendezvous is about 10km/s or about 22,369MPH

Of course, when they hit it'll still be "only" the damage from a 5km/sec impact, and not the damage of a 10km/sec impact. Mustn't forget that Mythbusters episode.

Of course at that speed I don't think it'll matter much for anything Human or Kerbal-made.

[Kryten]

Of course, when they hit it'll still be "only" the damage from a 5km/sec impact, and not the damage of a 10km/sec impact.

You must have misunderstood something; there's no difference between a collision between two objects moving 5km/s in opposite directions and one between a 10km/s and a static object.

[technicalfool]

You must have misunderstood something; there's no difference between a collision between two objects moving 5km/s in opposite directions and one between a 10km/s and a static object.

Thing is, it's not a static object. For objects of comparable mass and composition (say two cars, or two satellites) heading toward each other, that combined speed will still only result in the damage of two 5km/sec impacts. Again though, not like you'd care at those speeds.

[Kryten]

The only difference between the two cases is a change in the relative velocity of the observer by 5km/s.

[Red Iron Crown]

Thing is, it's not a static object. For objects of comparable mass and composition (say two cars, or two satellites) heading toward each other, that combined speed will still only result in the damage of two 5km/sec impacts. Again though, not like you'd care at those speeds.

I think you're mistaken about this. It is the total speed relative to each other that gets squared when calculating the energy, not the sum of the squares of their speeds relative to some third position.

[metaphor]

Of course, when they hit it'll still be "only" the damage from a 5km/sec impact, and not the damage of a 10km/sec impact. Mustn't forget that Mythbusters episode.

Of course at that speed I don't think it'll matter much for anything Human or Kerbal-made.

In the case of the cars, the deceleration of an impact between two cars each going 40 mph towards each other is the same as each car hitting a brick wall at 40 mph. It's also the same as one car hitting a parked car at 80 mph, but it's not the same as one car hitting a brick wall at 80 mph. The difference is that you have twice the crumple zone if there's two cars involved, so twice the stopping distance (half the acceleration).

If the situation is perfectly symmetric between the two cars, it's like each car is hitting an imaginary unbreakable wall which is along their axis of symmetry.

So an impact between two spacecraft going towards each other at 5 km/s would feel the same as an impact between a stationary spacecraft and one going at 10 km/s, and also the same as each spacecraft hitting a brick wall at 5 km/s (or a wall of neutronium, I doubt a brick wall would survive those speeds).

[Bobnova]

The two cars have to be identical or damn near it for the mythbusters result.

Do the same thing with a car and a semi truck and you'll find the car in more or less the same shape as if it hit a wall at 2x its velocity.

[z26]

One possible reason two cars facing each others at 40mph doesn't impact as strongly as one car hitting a wall at 80mph is because if the wall is "anchored" to the ground strongly enough, in this scenario it acts as if it has infinite mass (you can't push it back no matter how hard you try). Oh, and no crumple zone probably doesn't help.