# Collisions problem

1. Aug 17, 2007

### tonytnnt

Hi, I'm trying to figure out the number of g's something undergoes after being dropped and hitting the floor. So far I've figured out that I need the time it takes for the collision to occur. I know it's not instantaneous, but I can't find any information on it, so can you point me in the right direction? Are there tables with this information available?

P.S. If you need a scenario to figure out what I'm talking about (since I'm not sure if I've worded it correctly) if I were to drop my TI-89 graphing calculator from a height of about 2 meters, it should reach about 6.3 m/s in a vacuum. I need to figure out how many g's the calculator would experience when hitting a concrete floor (or slate or marble etc.)

Last edited: Aug 17, 2007
2. Aug 17, 2007

### ranger

All you need to do is find that acceleration (m/s2). To get the g-force, just divide that by the acceleration due to gravity.

3. Aug 17, 2007

### tonytnnt

Yeah I know I need to find the acceleration. I have the velocity, but I need the time it takes for the impact deformation to occur when the plastic (or some other material) hits the concrete.

4. Aug 17, 2007

### mgb_phys

It depends on the structure and rate of deformation of the thing and the floor. It is just about possible to model this using finite element programs but for an accurate answer you pretty much have to measure it experimentally.
In fact it is usually easier to measure the acceleration with embedded accelerometers and calculate the time.

5. Aug 17, 2007

### tonytnnt

Actually I'm trying to figure out what kind of tolerance I need for accelerometers The ones I want to use are rated for 3500g max, but I'm not sure how much I should account for. Oh, well. Trial and error I suppose.

6. Aug 17, 2007

### mgb_phys

I think 3500g is up in artillery round accelaration.
Typical 2-3 foot drop tests for laptops are around 200g.

7. Aug 18, 2007

### tonytnnt

thanks, looks like I might need to do some testing.