# Forces in Car Crashes

 Force on car Calculation of force on car Example of force on driver
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Work-energy principle

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# Example of Force on Car

(This initial example is cast in U.S. common units because most U.S. readers can make comparisons to known forces more easily in those terms. The calculation provides the results in SI units as well.)

### Vary the parameters of the collision

Note: these examples of forces during collisions use the average of force over distance rather than the average over time. The profile of force during a collision such as that of a car with a tree can be complex, whether expressed in terms of time or distance. The average over distance is used here because of its relationship to the conservation of energy and the work-energy principle.

 How do you define average force?
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Work-energy principle

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# Calculation of Force on Car

If the weight of the car is N = lb, corresponding to
mass = kg = slugs,
and the car is traveling with a speed:
v = m/s = km/hr = mi/hr,
then a crash which stopped the car in a distance d=m = ft
would result in an average impact force of

### Impact force F = N = lb = tons!!

You may change any data value. Clicking outside the box will then initiate a calculation of the impact force and conversion of the data value to the other types of units.

### Discussion of car crash scenario

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Work-energy principle

 HyperPhysics***** Mechanics R Nave
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