One less 458 in the world

[j2 lot]

What If 10 cars crash into each other at 10mph at the same time?

It's pensioner day at B&Q.

[Noops]

[Stevoraith]

Appears the Ferrari lost it at the roundabout at the junction of Queensferry Road & Queensferry Terrace. Spun several times and hit a Land Rover (might be a Range Rover) coming in the opposite direction.

If that's accurate then he must have been doing some speed past the school!

This picture shows a high wall in the background and as far as I can remember there's no such wall anywhere near the roundabout.



There is however a large wall like that on the Stewarts Melville side of the road along at the junction with Orchard Brae. So perhaps he's lost it coming out of the cross-roads at Orchard Brae, but I'd venture that he hasn't lost it at the roundabout- unless he has spun for a further 500m up the road after hitting the other vehicle which seems unlikely.

[robin]

It does appear to be parked facing back towards Edinburgh on the Stewart's side of the road. That wall is in the stretch between the two large office blocks and the church.

Force is the first derivative of momentum with respect to time. Thus it's a nonsense to equate momentum and force, e.g.

"Think also about this: If you applied a force equivalent to 100 km/h times the mass in the opposite direction of vehicle 1, that would actually make vehicle 1 change direction and go backwards at 50 km/h after the collision. Conversely it would also make vehicle 2 do the same. That doesn't happen."

What would such a force be? 100m/h is a speed, so base units would be m/s. Mass is mass, i.e. kg, so we have kg.m/s (otherwise known as momentum). Meanwhile force is measured in Newtons which are actually kg.m/s/s. So the units of momentum and force are incomparable and so cannot be equivalent in any way. You would have to apply that force over a period of time for it to become a change in momentum. Of course that's the difference between braking to a stop and crashing - the time over which the force is applied and the magnitude of the force.

All of the arguments around conservation of momentum would only be valid in the case where you first defined the system and then made sure there were no external forces acting on the system.

The only time a collision between two cars is the same as crashing into a stationary brick wall at the same speed is when the cars have equal but opposite momentum, which is never in the real world. The rest of the time the car with more momentum will experience less deceleration than were it to hit a brick wall and the car with less momentum would experience a higher deceleration (i.e. bigger crash). Take it to extremes and you'll see it's obvious. Imagine hitting a 10,000kg block of granite at 50mph. Now imagine hitting the same block when it's moving towards you at 50mph. I think you'll agree that the second case is going to be worse for you than the first.

So yes, you cannot just add the speeds in a collision, but equally you cannot ignore the speed/mass of the second vehicle when considering what deceleration the first vehicle will experience.

I hope that helps!

Cheers,
Robin

[Dark]

Appears the Ferrari lost it at the roundabout at the junction of Queensferry Road & Queensferry Terrace. Spun several times and hit a Land Rover (might be a Range Rover) coming in the opposite direction.

If that's accurate then he must have been doing some speed past the school!

This picture shows a high wall in the background and as far as I can remember there's no such wall anywhere near the roundabout.

There is however a large wall like that on the Stewarts Melville side of the road along at the junction with Orchard Brae. So perhaps he's lost it coming out of the cross-roads at Orchard Brae, but I'd venture that he hasn't lost it at the roundabout- unless he has spun for a further 500m up the road after hitting the other vehicle which seems unlikely.

Yeap, that's apparently what happened!

Although I didn't fully appreciate how far down the road he'd got! Lucky nobody was crossing at the pelican crossing outside the school gates.

[Peter]

It does appear to be parked facing back towards Edinburgh on the Stewart's side of the road. That wall is in the stretch between the two large office blocks and the church.

Force is the first derivative of momentum with respect to time. Thus it's a nonsense to equate momentum and force, e.g.

"Think also about this: If you applied a force equivalent to 100 km/h times the mass in the opposite direction of vehicle 1, that would actually make vehicle 1 change direction and go backwards at 50 km/h after the collision. Conversely it would also make vehicle 2 do the same. That doesn't happen."

What would such a force be? 100m/h is a speed, so base units would be m/s. Mass is mass, i.e. kg, so we have kg.m/s (otherwise known as momentum). Meanwhile force is measured in Newtons which are actually kg.m/s/s. So the units of momentum and force are incomparable and so cannot be equivalent in any way. You would have to apply that force over a period of time for it to become a change in momentum. Of course that's the difference between braking to a stop and crashing - the time over which the force is applied and the magnitude of the force.

All of the arguments around conservation of momentum would only be valid in the case where you first defined the system and then made sure there were no external forces acting on the system.

The only time a collision between two cars is the same as crashing into a stationary brick wall at the same speed is when the cars have equal but opposite momentum, which is never in the real world. The rest of the time the car with more momentum will experience less deceleration than were it to hit a brick wall and the car with less momentum would experience a higher deceleration (i.e. bigger crash). Take it to extremes and you'll see it's obvious. Imagine hitting a 10,000kg block of granite at 50mph. Now imagine hitting the same block when it's moving towards you at 50mph. I think you'll agree that the second case is going to be worse for you than the first.

So yes, you cannot just add the speeds in a collision, but equally you cannot ignore the speed/mass of the second vehicle when considering what deceleration the first vehicle will experience.

I hope that helps!

Cheers,
Robin

You got back ok then...LOL!!!


---
I am here: http://maps.google.com/maps?ll=56.043448,-3.427184

[Noops]

What a waste , arse

[tut]

At least it was not a Spider.

http://www.topgear.com/uk/car-news/fern ... 2011-09-12

tut

[I-Mac]

Physics 101:

Hitting a landrover at 40mph.... Is Exactly like hitting a stone wall at 40mph

[robin]

I believe it was a BMW, actually, although it has been reported as a Land Rover.

[Dominic]

Don't get me wrong, as others have said, it would appear the driver must have been exceeding the speed limit from the damage to the car, which I do not condone. However, lets not assume things, and just because a sports car was involved it was not necessarily the sport's car drivers' fault. There was apparently another vehicle involved. Say it was doing 40 MPH, the Fezza was doing 30 MPH, and the hit head on; that would be a 70 MPH impact, possibly with no blame to the sports car. We all know how the press loves to get hold of a story like this, and will not let mere facts get in the way of a good story.

What did I start ??!!??

I was just trying to make the point that all may not appear as it is presented.

[ClarkyBoy]

Physics 101:

Hitting a landrover at 40mph.... Is Exactly like hitting a stone wall at 40mph

Im not exactly sure on that iain,

heres my logic - i have seen you r land rover mount a granite wall at a little under 40 mph and it drove clean over the top of it, so by that thinking, hitting a landy would be worse than a granite wall

what a waste of a nice car though

[Doc883]

One of the parents from Stew Mel was injured in the accident, in hospital with serious leg injuries.
However not sure if they were one of the drivers or a pedestrian. From the photos you'd think it was the Ferrari driver, will try to find out more details later.

Just found out my wife is pals with the wife of the driver that was injured in the Landrover Discovery. He suffered multiple fractures to his leg and could be off his work for up to 12 months to fully recover (Easyjet Pilot). Will be 3 months before he can even stand up and attempt to walk. His daughter was also in the car but luckily she was up front on the passenger side so away from the impact area and managed to walk away from the crash.