# HELP: How would you measure the force of an expolsion?

1. Aug 26, 2009

### Kool-Aid

I am trying to test different fuel types(for science fair, I am a sophomore in high school)
and i was wondering if anyone new something that could be bought or made to measure the force of an explosion. My current ideas don't seem like they would be very accurate.

Any help at all would be greatly appreciated, even if its just a rambling thought, it may be useful to me.

Thanks for your help, and Hi seeing as this is my first post, I hope I can help others while i'm
here.

2. Aug 26, 2009

### jasc15

You might be looking for impulse. I did a project once where i measured the thrust of model rocket motors over time, and calculated their total impulse. Does this sound like what you are after?

3. Aug 26, 2009

### FredGarvin

You would most likely use high response pressure transducers to try to capture the pressure wave.

4. Aug 26, 2009

### Danger

That sounds reasonable, Jasc. The method would have to depend upon the general magnitude of the explosion, though. I'm assuming, since it's for a science fair, that it will be pretty small.
If the explosion can be set up so as to create a spherical shockwave, a few strategically placed seismic sensors, such as piezoelectric elements or mini-accelerometers, should be able to extrapolate the overall force.

edit: You sneaked in on me again, Fred. Good idea.

5. Aug 26, 2009

### Staff: Mentor

Welcome to the PF.

First of all, explosions are usually discouraged as high school science fair subjects. Do your teachers and mentors know that this is what you want to work on?

Second, if they are okay with small explosions in your experiments, and are satisfied that you are using good safety precautions with the explosion part and the flammable liquid handling part (both of which would need to be part of your report, obviously), then you need to devise a way to measure the relative expansion of the rapid combustion / explosion of each fuel. One safe way is to have the explosion confined to a strong cylinder, where one end is open and covered by a movable stopper. You set off the combustion inside, and measure how far the stopper is displaced.

As an illustration of a safer science fair project, but along the same lines, berkeboy did a project that measured the effectiveness of different soda-type explosive expansions. He set up a 2 liter plastic bottle and a cork as a projectile launcher at 45 degrees, and loaded different test mixtures into the bottle and sealed them with the cork. The cork launch distances were recorded as a measure of the quality of the mixture...

I think his longest launch was in the neighborhood of 15 meters. He had fun with that project...

6. Aug 27, 2009

### TonopahJoe

There is a consulting firm based in Norway called GexCon that specializes in computer modeling and analysis of explosive gasses and liquids. Their clients include operators of off-shore drilling platforms, petrochemical plants, and so on. They have a downloadable "Gas Explosion Handbook" that explains the physics quite well. Check out Gexcon.com

7. Aug 27, 2009

### Kool-Aid

Thanks for all the great replies, I think I may have found something else out.

What do you guys think about using a bomb calorimeter to measure the heat produced and convert it into calories and also Joules?(because its the SI accepted measure)

It seems like that would be the most accurate, I had also been thinking along the lines of your cork idea berkeman but the cork would be altered with every trail(Burned, size changes, etc.) so it wouldn't be very accurate, plus there would be to many other variables I couldn't control.

My physics teacher at my school can teach me how to make a fairly accurate bomb calorimeter, so thats not a problem.

Oh and the problem with using a Gas explosion handbook like what Tonopah recommended is that I need to do some of the experimentation or it will not have a good enough effect on the judge.

And yes this is completely approved with my teacher. When I posted this last night it was still a little bit of a rough idea and i didn't explain it well enough so heres some more accurately what i plan to do is measure the amount of energy produced by X amount of each fuel type (CNG, gasoline, Different grades of ethanol, and other possible fuels) then compare that with all other factors concerning its viability of becoming a good alternative fuel.

So what do you think of the use of a bomb calorimeter in this or some other ideas? Thanks so much for all the help.

8. Aug 28, 2009

### Staff: Mentor

Well, I think that this subject is not appropriate for the PF. Sorry. Good luck to you and your high school advisor on this project. There are other web-based sources of information on this subject. As you can tell by re-reading the PF Rules link at the top of the page, we won't be of help on this.