Impact force question

[mdv638]

I have a large mass of steel moving at 5 miles per hour. I have been asked to find the impact force so I can do some other calculations. I’m having a bit of trouble getting started. Currently I have assumed that there is a bumper on it, but I think there may be something better. Does anybody have any suggestions on how to calculate the impact force.

 

[IRstuff]

With a known bumper, you can simply use the kinetic energy of the mass and equate that to the amount of work required to compress the bumper. The work divided by the compression distance is the average force.

TTFN

 

[SlideRuleEra]

You need to know what happens to the "target" it hits - if the "target" is very massive and essentially immovable AND the 5 mph moving object comes to, and remains at a complete stop after the impact, you could use Newton's second law of motion: F= MA

Based on the materials involved measure or estimate the time to go from 5 mph to zero mph, you know the mass - you now have the impact force.

An ideal situation of course, but another way to start.

 

[GregLocock]

You have to decide on the interface between the moving body and the target. Typically in engineering situations we use a spring and a damper. In a crash we use a structure that crumples, which more nearly approximates a constant force. This is the easiest to work out, using F=m.a and v^2=2.a.s

However that is the least likely scenario.

The spring and damper is a bit more difficult to work out, but it is only a single degree of freedom system, and if you ignore the damping in the first quarter cycle then it is quite simple, since the energy stored in the spring when fully compressed is 1/2*k*x^2, and this is equal to the KE of the mass, 1/2*m*v^2

If you search through the threads you will find a long one on the impact of a steel ball on a steel plate.



Cheers

Greg Locock