Being hit by a car or a bike

[Glom]

There is science to be looked at from a discussion I had elsewhere.

I'm thinking of a high street type environment, where cars will not (or at least should not) be doing more than about 30 km/h but an Audi cyclist might be tearing through at the same speed.

A gross simplification compares momentum and/or energy but that's misleading because the car at least won't be stopped by the impact so the entirety of additional momentum and energy won't be transferred to the victim.

The shape of the vehicle is the major issue. Modern cars are designed to be as kind to the cows they catch as possible ( no more of that of that Jaguar ornament and the Mercedes ornament retracts). The victim is supposed to go over the bonnet and perhaps fall off the side. A bike on the other hand presents a rather nasty looking profile to be hit with.

Remember, either vehicle is doing 30 km/h so the car isn't travelling at car-ish speeds.

Which would be most likely to cause more serious injury?

[BazBear]

A gross simplification compares momentum and/or energy but that's misleading because the car at least won't be stopped by the impact so the entirety of additional momentum and energy won't be transferred to the victim.

Wouldn't the fact that car doesn't stop mean there would be an even larger transfer of energy and momentum to the victim?

Of course that's only one of the factors in your scenario, and my gut feeling is I'd rather take my chances with the "friendlier" front profile of the car.

[Glom]

A gross simplification compares momentum and/or energy but that's misleading because the car at least won't be stopped by the impact so the entirety of additional momentum and energy won't be transferred to the victim.

Wouldn't the fact that car doesn't stop mean there would be an even larger transfer of energy and momentum to the victim?

Of course that's only one of the factors in your scenario, and my gut feeling is I'd rather take my chances with the "friendlier" front profile of the car.

I'd expect the opposite. If the change in speed is small then the energy transferred is small squared.

[Allan F]

A gross simplification compares momentum and/or energy but that's misleading because the car at least won't be stopped by the impact so the entirety of additional momentum and energy won't be transferred to the victim.

Wouldn't the fact that car doesn't stop mean there would be an even larger transfer of energy and momentum to the victim?

Of course that's only one of the factors in your scenario, and my gut feeling is I'd rather take my chances with the "friendlier" front profile of the car.

I'd expect the opposite. If the change in speed is small then the energy transferred is small squared.

Multiply by mass. 1500 kg vs. 100 kg. for example. If the masses on the other hand, are about equal, they share the energy. Also, a bicycle and -cyclist isn't rigid as a car is, so the collision is drawn out over a longer time.

[Al Johnston]

In the UK about one pedestrian per annum is killed by collision with a cyclist (statistics don't record which one). About 3,000 per year are killed by motor vehicles.

I don't think there are 3,000 cars for every bike on the road...

I also suspect the shape of cars has some optimisation to go - there are some very hard head-shattering bits of engine under that relatively flexible bonnet,,,

[Allan F]

The windshield is quite a killer too - head injuries.

[Daniel Dravot]

I'd expect the opposite. If the change in speed is small then the energy transferred is small squared.

It's small times big.

v₀²-v₁²=(v₀-v₁)(v₀+v₁)

Which is still less than big times big.

[Glom]

In the UK about one pedestrian per annum is killed by collision with a cyclist (statistics don't record which one). About 3,000 per year are killed by motor vehicles.

I don't think there are 3,000 cars for every bike on the road...

I also suspect the shape of cars has some optimisation to go - there are some very hard head-shattering bits of engine under that relatively flexible bonnet,,,

True but not entirely relevant since that includes accidents in all situations. This example focuses on a high street where the cars are crawling along but the bike may still be going relatively fast.

I also just checked the stats since your figures sounded unfamiliar. According to DfT, for FY11-12, the number of people killed in "road accidents" was 1,870. That would definitely include occupants of cars in car on car violence and accidents with motor vehicles other than cars.

That's just an FYI. Death is unlikely in either case in the example I posed since one is a car travelling at low speed and the other is a bike. It's more about the level of injury.

[Glom]

A gross simplification compares momentum and/or energy but that's misleading because the car at least won't be stopped by the impact so the entirety of additional momentum and energy won't be transferred to the victim.

Wouldn't the fact that car doesn't stop mean there would be an even larger transfer of energy and momentum to the victim?

Of course that's only one of the factors in your scenario, and my gut feeling is I'd rather take my chances with the "friendlier" front profile of the car.

I'd expect the opposite. If the change in speed is small then the energy transferred is small squared.

Multiply by mass. 1500 kg vs. 100 kg. for example. If the masses on the other hand, are about equal, they share the energy. Also, a bicycle and -cyclist isn't rigid as a car is, so the collision is drawn out over a longer time.

My concern is how the components of the bike are a bit more impaling. It's blunt force trauma vs whatever being smacked by a crowbar is.

[Allan F]

If you're hit by the handlebar, it will turn and deflect, not deliver the full force, while the person on top would go flying. The structure is not really able to deliver the force. The most dangerous thing (imho) is if you were hit by the person, not the bike. Getting someone's skull in the face is never a good idea.