Force of the average car crash

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Discussion Overview

The discussion revolves around the forces generated during car crashes, particularly focusing on the average force experienced when a car impacts a solid object, such as a wall. Participants are exploring the physics behind these forces, including calculations related to kinetic energy, impulse, and momentum, as well as seeking relevant research and data on the topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about existing research on the average force generated during car crashes, specifically when a car hits a wall.
  • Another participant suggests a website for reference but notes that a search did not yield specific data on forces in car crashes.
  • A participant expresses curiosity about the magnitude of 500,000 Newtons and asks for a comparison to understand if it is a large force.
  • It is stated that 500,000 Newtons is a significant amount of force, and a method is proposed to determine average force based on the distance the car's center of mass travels after impact.
  • A calculation is presented for a specific scenario involving a 4 m long car with a mass of 1200 kg moving at 30 m/s, leading to a derived force of 270,000 Newtons, with a suggestion that the initial figure of 500,000 Newtons may be realistic.
  • A participant introduces the concept of impulse, explaining that the average force can be calculated by dividing the impulse by the duration of the crash, and mentions the need for a force-time curve to determine peak force.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding and curiosity about the forces involved in car crashes, but there is no consensus on specific values or methods for calculating these forces. Multiple approaches and calculations are presented without resolution of which is most accurate.

Contextual Notes

Some calculations rely on assumptions about the mass distribution of the car and the duration of the crash, which may not be universally applicable. The discussion also highlights the lack of readily available data on the topic.

Da Apprentice
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I was wondering is there any research that has been done into the typical amount of force generated duing a car crash. Eg, when the car hits a wall for example does anyone know the average force needed to stop it? thoght it'd be interesting to know since I'm doing similar research on this topic in Physics at the moment.

Thanks,
 
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Da Apprentice said:
I was wondering is there any research that has been done into the typical amount of force generated duing a car crash. Eg, when the car hits a wall for example does anyone know the average force needed to stop it? thoght it'd be interesting to know since I'm doing similar research on this topic in Physics at the moment.

Thanks,
The http://hypertextbook.com/facts/index-topics.shtml" is a good site for such things. The information is usually well referenced. A quick search, though, does not show data on forces in car crashes. A more thorough search might.

I think the Myth Busters did something on this. Not the level of rigo you probably want, but it might provide a lead...
 
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Yeah searched all through there... got nothing... can someone please tell me how much 500,000N is equivalent to... Is this a large Force?
 
Yes, that's a fairly large amount of force (a bit over a hundred thousand pounds). If all you're looking for is the average force, simply look at how far the car's center of mass traveled after impact. From that, you can determine acceleration, and thus determine force.
 
For a 4 m long car of mass 1200 kg moving at 30 m/s, the kinetic energy is
.5mv2 = 540000 Joules

If we use cjl's approximation and take the center of mass at the center of the car, the work needed to stop the car is
FD = F(2m) = 540000 Joules
F = 270000 Newtons

I suspect the center of mass is farther forward (given the mass of the engine block) so the 500000N figure looks realistic.

I am surprised by that magnitude.
 
I like to look at this in terms of impulse, i.e., change in momentum.

If you know the mass (m) and the speed (v) of the car initially, and we assume that the car comes to a stop after the crash, the total impulse delivered to the car is m*v.

If you want to know the average force applied to the car during the crash, divide the impulse by the duration of the crash.

To find the peak force, you will need to have a curve for the relative change of the force over time during the crash. If you scale this curve so that its integral is the impulse then the peak of the curve is the peak force.

Cheers,
Chris
 

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