Comments on: Mythbusters on Head-on Collisions

By: ????????????

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By: Kelly

Kelly — Sat, 09 Sep 2017 02:54:26 +0000

Here’s what you knuckleheads aren’t understanding… it’s actually not about what the cars experience, but what the PEOPLE driving the car experience. They are not only feeling half of the impact, they are feeling 100% of the force of the impact.

By: jay

jay — Fri, 24 Feb 2017 11:00:58 +0000

they didn’t actually test the myth – a third test of one car going 100 mph hitting a stationary one was the missing point. Assuming the two masses are the same and ignoring road friction and other minor annoyances, the math is pretty straightforward . if a moving mass hits a stationary mass and neither deforms (think of a newtons cradle with only two balls) the moving mass stops and the second accelerates away and is soon moving at the same speed and direction that the first had. If the masses connect and lock together but do not deform, the new blob of twice the mass will move in the same direction as the initially moving mass, but (in this case) at around 70.7 mph. If both masses deform (momentum, kinetic energy converting into deformation and heat) both masses travel in the same direction as the initial mass at some speed less than 70.7 mph – and because they are still moving, (and still have some energy) the deformation to each is likely to look like 50mph for vehicles with moderate deformability IMHO. Look at it one more way, if a moving car hit a stationary car backed up to touch the wall, at 50mph, some energy would deform the moving car, and both ends of the stationary one. At 100 mph, the deformation would be 4X the energy spread out where the two vehicles touch each other and where one touches the wall The myth IS busted no matter what.
TL;DR one car, 50mph, strong wall – energy converted to smush =X, car stops. Two cars, each 50mph, hit each other – energy converted to smush =2X, each gets half, both stop. Two cars, one 100mph and the other zero, energy AVAILABLE to convert to smush =4X … identical smush would be related to the final speed of the still moving combined mass..
super TL;DR: one car moving at 50, hits wall and stops, energy is X, car absorbs it. Two cars moving at 50 hit each other, energy is 2X spread over 2 cars, therefore same outcome as hitting the wall – all STOP. if one moving 2 times speed and other zero, energy is 4X the lower speed, both cars will smush, and the combined mass is STILL moving after the collision (with the possibility for more smushing – where is that wall exactly?).
Myth busted with math.

By: David

David — Sun, 20 Nov 2016 16:42:14 +0000

This is all fun theory but bottomline:

Head-on collisions are VERY DANGEROUS!

Better to nudge or side swipe car going in same direction or hit a small stationary object.

P.s. who would drive head on into a solid wall?

By: Martin Pedersen

Martin Pedersen — Fri, 11 Nov 2016 07:18:34 +0000

Hello.
I was thinking about the test with the 2 cars crashing with 50 mp/h. But what if car 1 was at 0 mp/h and car 2 at 100 mp/h.
Same result?

By: Akash Phalak

Akash Phalak — Thu, 06 Oct 2016 11:24:51 +0000

hi guys, In my project of accident detection i m using accelerometer to detect impact and i m placing it at footweel(driver foot place) in car so which g value sensor do i need for appropriate detection.
i m confuse about 40 to 50 or 100g sensor. i think the main concern here is the place where we can place our sensor(accelerometer).

By: Brainstorms

Brainstorms — Sun, 11 Sep 2016 21:28:38 +0000

Question, don’t miss the assumptions in your #42 that the wall is “solid and immutable”, and therefore absorbs some of the energy of impact without any substantial damage…

Whereas your “not moving car” differs considerably: It is SIGNIFICANTLY lower in mass than the wall (which is presumed to be so massive that it can be treated as having essentially infinite mass for the purposes of calculating the collision effects), and it is “plastic”, in that the energy of collision will very significantly –and easily– deform the second car.

The deformation will absorb some of the energy of collision, while having a mass comparable to the moving car will result in it acquiring a velocity post-impact.

In short, you have a very different physics problem if you replace the wall with a stationary car…

By: Question

Question — Sun, 11 Sep 2016 21:04:14 +0000

I get it for hitting a wall that is that force is mainly distributed to crush the car while wall provided it doesnt move and is really solid doesnt absorb much.
But…
If we would replace the wall with not moving car then that comparision (2*stat = 1*head on) will be true right?

By: 2016 American muscle cars Crash Test - Video

2016 American muscle cars Crash Test - Video — Tue, 24 May 2016 23:15:13 +0000

[…] did a good job on that issue of mass and speed in collisions. Turns out ol' Newton was right:http://scienceblogs.com/gregladen/20…on-collisions/ At the same time – they may have gotten it wrong, while getting it right..right?!? The mass of two […]

By: Doug

Doug — Fri, 20 May 2016 20:23:07 +0000

david —

To answer your question, since your car is going a bit slower than the other, and since we don’t care about hurting anybody else — all we care about is ourselves — and I assume that the tunnel wall is 100% rigid and immovable … it would be slightly better to hit them head on than to hit the tunnel wall.

And if the two speeds were equal, it wouldn’t matter which one you did — both would result in approximately equal damage to your car and yourself.