# Homework Help: Extended essay topic question

1. Feb 15, 2004

### Vodka

i'm starting [again] a physics topic for extended essay for IB...my last few topics haven't worked due to technical difficulties [ie: can't complete experiments, lack of avaliable resources, etc] so my new idea for a topic is firearms. the lab can easily be done by going to a shooting range sometime this week.

i'm looking to have at least three comprehensive subthesis', each focusing on a field of physics that is directly relevant. my ideas for two so far are:

momentum laws - primary/secondary recoil, terminal ballistics etc, all with a few relevant equations.

gas laws - actual firing of gun, how it cycles, noise generated and how it could be reduced, might be able to get some relevent figures [ratio of gunpowder grain to gaseous products]

i dunno what to do the last one on..kinematics and sound could be plasuable if i need, but are both sortof weak. so any sortof help would be great. thanks :)

2. Feb 15, 2004

### marcus

vodka, I dont have enough knowledge/ideas about rifles to help
except to dig up from memory an experiment that
a Freshman physics (like 1A or 1B) did years ago in class (!) with a 22.

I guess it was after class had ended.

there was a wooden frame like a sawhorse from which was
suspended a pendulum
and the pendulum bob was a large block of wood of known mass into which the bullet would embed itself on impact

the 22 rifle, IIRC, was clamped in a vise on the experiment bench.

an observer from the side (far enough away for safety)
could see what angle the pendulum swung

the bullet mass was determined
it was fired into the pendulum, which was hanging at rest,

the momentum imparted to the combined mass of wood block and slug
was determined from the angle of swing

the speed of the slug was calculated

perhaps this is a standard procedure
(i mention it only because it is all I got that is remotely
applicable)

BTW this seems potentially dangerous to me because the suspension of the pendulum is critical and the slug must hit dead center to avoid putting a torque on the block.

I'm not recommending this! It is just all I've seen done with firearms in first year college physics.

Last edited: Feb 15, 2004
3. Feb 15, 2004

### Moose352

I did a similar experiment, except with an airsoft gun. It was hard to get a correct angle reading, but once I did, i was surprised by the accuracy of the experiment. The gun shot 280 FPS according to the manufacturer. My experiment found the average velocity around 260-270 FPS. Not bad!

4. Feb 16, 2004

### Vodka

on a completely tangential point, what gun do you have? ^_^

i got a mk23 socom kit and a tm mp5a4hg. it currently has a navy flashhider, clawmount, guarder 11stage RDS, 2 and 3 pt slings, 2x hicaps, 5x locaps, an ICS triplerail handgrip, mag clamp, large 8.4 3000mah battery in a case. in the process of purchasing a vertical handgrip, and looking into a better flashlight and laser pointer. i've spent so much, its obscene.

i get to spend about twice what you would for the same thing because of the stoopid importation laws in canada. ah well. least we get trademarks and unpainted barrels