Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Prove this wrong!

  1. Jan 31, 2009 #1
    mom says my airsoft damaged her car. i call bs! need a drawn out formula to prove this.
    given:

    plastic bb at 6mm in size
    the bb weighs .30g
    and moves at about 300FPS


    the car was 40 yards away. (120ft)

    i would suppose impact damage is mini here if any. the bb is plastic the car is metal?
    help needed bad!!! thanks guys.
     
  2. jcsd
  3. Jan 31, 2009 #2

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    How severe was the damage? Did the car explode?
     
  4. Jan 31, 2009 #3
    Lol it doesn't need a formula to prove that wrong. It's pretty hard to imagine that the car was dented by your airsoft gun. I would use a formula but I'm not entirely sure how to put in 300 FPS into an equation. FPS could mean either of two things to me;

    Foot-pound-second

    or

    Feet Per Second

    Both are much different.
     
  5. Jan 31, 2009 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    FPS obviously means feet per second. Just as obviously (but apparently not), using your Mom's car for as a target with a projectile moving at 200+ miles per hour is not a good idea.
     
  6. Jan 31, 2009 #5
    Unfortunately the facts are not in your favor. Even making the assumptions favorable to you, the pressure at the point of impact was likely at least 50 KiloPascals. For comparison, the pressure exerted by a slim woman if she put all her weight on one high heel would be 110 KiloPascals.
     
  7. Jan 31, 2009 #6

    Nabeshin

    User Avatar
    Science Advisor

    The moral of the story is: Don't shoot bb guns at cars.
     
  8. Jan 31, 2009 #7
    i didnt! she thinks it might happen. and its feet per second. maybe like a impact fomula.

    its enough to go into a can. but with an object weighing in at .30 grams. after 40ish feet it quickly losses speed. the wind anything could even throw it off coarse.

    and the bb is plastic!
     
  9. Jan 31, 2009 #8
    If you are so sure your gun couldn't do this, demonstrate it to her by shooting at a clean spot on the car. Works much better than formulas. On the other hand, if you were wrong, you might get in trouble.
     
  10. Jan 31, 2009 #9
    You originally stated 40 yards, now you've stated 40 feet. That's quite a difference.

    Regardless, velocity drastically increases the kinetic energy of an object. Each time velocity has been doubled, the kinetic energy has been quadrupled, so that which is small becomes mighty by the time 300 FPS (204.5 MPH) is achieved.

    Additionally, the lesser the distance provided for the object to come to a complete stop, as is the case for the BB's, the greater will be the impact damage. If those plastics BB's can pierce a can, they'll likely be able to damage the paint if nothing else even at 40 yards. There's a good chance that they may put little dings in the sheet metal of the car, but realistically, we're not able to assess the damage from here.
     
  11. Jan 31, 2009 #10

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    However air resistance also quadruples, so the pellet may well be doing much less than that by the time it gets to the car, especially if it's 40yrds away.

    Anyway it was very irresponsible of you - airguns should only be fired at younger brothers (kidding!)
     
  12. Jan 31, 2009 #11

    turbo

    User Avatar
    Gold Member

    Ooh!

    I have an air rifle that I bought a couple of years ago when red squirrels started getting REAL destructive around here. It is a Daisy single pump (you have to be in good shape to pump it that one time) break-barrel pellet gun rated for 1000 fps. I can shoot it at a tin can 30-40 feet away, and the can will barely move. Nice neat holes in front and back, because the can did not offer enough resistance to the pellet to slow it down and strip off some of its momentum. Due to the action of the spring-loaded piston, the rifle does not recoil - it "fore-coils" if I can coin a word, and conventional rifle scopes cannot be fitted to this rifle, since they are designed to resist front-to-back recoil.

    To get back to the OP and avoid totally derailing this thread, I suggest that he visit a junk-yard or some other place with "sacrificial" vehicles and test the air-soft gun's ability to dent sheet metal before shooting at his mother's car as a demonstration. Since most salvage businesses want to keep sheet-metal as pristine as possible for future re-sale, I suggest doing the experiment at night. OK, just kidding, but there should be someplace around that has some vehicles just waiting to be scrapped (not parted out).
     
  13. Jan 31, 2009 #12
    Experiment evidence is in order. Shoot the car again with several pellets at an undamaged region and see if any leave dents.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?