Nascar Gets a Catcher's Mitt

Just curious - how does one calculate G-force knowing only the velocity of a moving object coming to rest in a case like this? An energy equation? I suppose a mass would have to be assumed.

Just as a guess, mass would certainly have something to do with it, but I believe the major contributor would be how the vehicle self destructs as it hits the wall. If the vehicle were a solid block of aluminum when it hit the wall, the g forces would be horrendous, because the deceleration would take place almost instantaneously.

Modern passenger vehicles are designed to fold up like an accordian in a crash, but this takes time. Extending the deceleration over time means that the G forces are less for the occupant(s) of the vehicle, resulting in less broken people.

I do long for my old '56 Chevy though, with real bumpers, with which I could push and pull things without having to worry about breaking it.

Bill

Force = Mass X Acceleration

Force X Time = Mass X Velocity

Substitute for Force

Mass X Acceleration X Time = Mass X Velocity

Mass drops out

Acceleration X Time = Velocity

Solve for Acceleration

Acceleration = Velocity X Time

Gravity is either 9.81 m/s squared or 32.2 ft/s squared

So your really just need the speed of the car at impact, and how long impact occured.

Okay - with this approach you assume a delta t, delta v is known, and accelleration is easily calculated (assuming it is constant). Still wondering how the author came up with 100G - an arbitrary assumption of delta t for a crashing race car? But I get his point.

And there you have the issue. How do you absolutely time the impact? Until everyone agrees with t₀ and t_f you'll get 100G answers.

Just for the heck of it, lets look at numbers. 55 mph corresponds to 80.666 feet per second. Now lets assume stopping times starting with 1 msec (.001 sec). We can make a table showing time, deceleration in feet / second², and using the 32.2 feet/sec² mentioned above, translate into g forces.

TIME (sec) DECELERATION G FORCE

.001 80666 FT/SEC² 2505 G

.01 8066 FT/SEC² 250.5 G

.1 806.6 FT/SEC² 25.05 G

1 80.66 FT/SEC² 2.505 G

Bill