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Easy way to figure FPS

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Unread postAuthor: jrrdw » Sat Oct 14, 2006 5:29 am

"Zero is a perfectly legitimate entry into such a unit-conversion formula."

I'm interested in knowing how so when we are talking about a moveing, or stationary object? Other then makeing a tenth, example : "50", not "0".
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Unread postAuthor: boilingleadbath » Sat Oct 14, 2006 7:38 pm

1 CM = 1/2.45 inch
0 CM = ? inch

0 CM = 0 inch, that's what!

1 mile = 5280 feet
0 mile = 0 feet!

1 hour = 3600 seconds
0 hours = 0 seconds!

1 MPH = 1/3600 MPsecond
0 MPH = 0 MPS

1 MPH = (1/3600 * 5280) feet/second
0 MPH = 0 feet/second

+++++

If that's not enough, let's solve your equation for 1 MPH:
1 MPH = (1 + .5 + 7) fps = 8.5 fps
Now, this means that, in an hour, the projectile which travels at one MILE PER HOUR has moved 30600 feet... or (in other words) ~5.8 miles.
Now, isn't it a tad odd that something that moves 1 mile PER HOUR has moved 5.8 miles IN AN HOUR?
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Unread postAuthor: jrrdw » Sat Oct 14, 2006 8:10 pm

Makes perfect sence if your measureing by the hour, but where not measureing by the hour, where measureing by the second. No projectile from a spud gun is going to travel 3600 seconds, or for a mile. I think your trying to put to much into a simple equation. Do you think the state police would use this equation if it didn't produce accuret results for accedend investagations? They been doing it this way for years and years. The funny thing is, your math is correct, and yes it is odd that they use this equation, when it checks out in the long run like it does.
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Unread postAuthor: schmanman » Sat Oct 14, 2006 8:19 pm

boilingleadbath wrote:Now, isn't it a tad odd that something that moves 1 mile PER HOUR has moved 5.8 miles IN AN HOUR?


yeah, that is weird.
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Unread postAuthor: MrCrowley » Sat Oct 14, 2006 8:55 pm

jrrdw wrote:Makes perfect sence if your measureing by the hour, but where not measureing by the hour, where measureing by the second. No projectile from a spud gun is going to travel 3600 seconds, or for a mile. I think your trying to put to much into a simple equation. Do you think the state police would use this equation if it didn't produce accuret results for accedend investagations? They been doing it this way for years and years. The funny thing is, your math is correct, and yes it is odd that they use this equation, when it checks out in the long run like it does.


in the long run its a tad off by a few fps,but what happens if your speed is changing like for 59min your going 5.8mph and at the last minute you change your speed to 1mph,then youve gone 5.8mph in one hour :D jokes :wink:
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Unread postAuthor: boilingleadbath » Sun Oct 15, 2006 2:38 pm

Something doesn't have to travel for an entire hour at a single speed for one to state the speed in MPH, in the same way a potato that gets snuffed out of existance after .1 seconds can still have it's speed be measured in FPS.

...and you are confusing one specific state policeman who came up with a way to amuse himself during long shifts with the entire force (and/or the judiciary system).
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Unread postAuthor: Flinchy » Sun Oct 15, 2006 3:18 pm

yeah by the way guys, if you can manage to find the muzzel velocity you can use this equation to determine how far the projectile will go at any angle.

Distance = Vo x sin(angle)squared
---------------------
Gravity

i think thats right, this doesn't include air resistance though, i don't know those ones yet. this one might be wrong, correct me if your familiar with this.

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Unread postAuthor: jrrdw » Sun Oct 15, 2006 6:03 pm

No not confussed, this guy was accident investigation, he had no reason to bs me. We were telling each other about the car recks we were in, but enough of this i think he's rite, you don't, no biggie.
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Unread postAuthor: POS » Tue Oct 31, 2006 5:05 pm

jrrdw wrote:I think theres a easier way, measure from the end of your barrel to the target, get a friend to time the shot, how ever much time it took the ammo to hit the target, is how many feet per second. Pretty easy, huh.


That should be rocket science ... :roll:

How the hell could that be acurate, is the projectile only flies 0.1 seconds. If you clock off at 0.2 seconds, the speed is already reduced by 50 %

It's a little acurate if you do distance shots, but then the ammo loses a lot of speed in mid air, so this is a not to use methode !

The sound-methode of Extrusion is exelent. Nice finding my friend !!

However, to be more acurate, you should place the microphone just in the middle between the tarket and the barrel.

Sound takes a (short) while to move from the place it starts to the place the microphone is in. So if you put the mike close to the target, the sound of the barrel will reach the mike, when the ammo is already in mid air, and flying for a short period of time. If you calculate the speed like this, the outcome is less than the actual speed. (due to the difference in speed between the ammo and the sound)

If you put the mike right in the middle of the traject, the sound will need as much time to get from the barrel to the mike, as from the target to the mike. Whatever the speed of sound is, doens't mather in this case, cause the time between the start of the barrelsound and the targetsound will be exacly the time the ammo needs to get there, so you have a exact outcome.

Extrusion, you should try this once, so you can compare the two results. You will see that the result of your measurement will be less than the measurement when the mike is right in the middle.
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Unread postAuthor: POS » Tue Oct 31, 2006 5:21 pm

jrrdw wrote:Makes perfect sence if your measureing by the hour, but where not measureing by the hour, where measureing by the second. No projectile from a spud gun is going to travel 3600 seconds, or for a mile. I think your trying to put to much into a simple equation. Do you think the state police would use this equation if it didn't produce accuret results for accedend investagations? They been doing it this way for years and years. The funny thing is, your math is correct, and yes it is odd that they use this equation, when it checks out in the long run like it does.


Man oh man, what is wrong with you guys. The speed of an object will increase when the pressure behind it, is bigger that the pressure in front of it. So in a barrel, when shot, the projectile will accelerate. When it leaves the barrel, the first mm's the pressure is still higher behind it, it will still increase it's speed. But from the moment the pressure in front is bigger, or even equal to the pressure behind it, it sill start to slow down.

So from the moment the object is at least about 1/2 of the ID of the barrel away from the barrel, it starts to slow down. Speed changes constantly, unless you are in outer space, and even then it changes due to the gravity all around.

However, when a object hypoteticaly flies at the same speed during a period of time, and the speed is lets say 600 fps, the object will fly 600 feet far in one second.

Accordingly to that, the object will fly 1 mile, if it has a speed of 1 MPH and it flies during 1 hour. It can never fly 5.8 miles in an hour, at 1 MPH during the entire hour. (Unless it uses a time machine)

Thsi is no rocket science, this is pure logica.
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Unread postAuthor: POS » Tue Oct 31, 2006 5:33 pm

jrrdw wrote:Where did this - " ...50 mph is 73 mph, and 0 MPH is NOT 7 fps" come from?

I never said that, what i'm saying is, if your driveing 50mph you measure fps by doing this, - 50 (or any speed your driveing) divide by 2, gives you 25, add 25 to 50, = 75, add 7,= 82, your traveling 82 fps.

example 2 - your driveing 70 mph, divide by 2, = 35, add 35 to 70, = 105 +7 = 112, at 70 mph your travling 112 fps.


Man, what a bad cop. He is so wrong.

You should take the MPH, multiply it by 1.47 (cause 1 MPH is the same as 1.47 fps) That's it. Easy as that.

So 50 MPH (times 1.47) is 73.5 fps
70 MPH is 102.9 fps
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Unread postAuthor: Dazza_Bo » Sat Nov 04, 2006 1:10 am

just becuse your moving 0 mph doesnt mean your not moving. you can just be moving so slowly that you dont move over 1 mph meaning you are moving at 0 miles every hour. you could be moving 1 mile per 2 hours but technically you'd still be moving 0 miles per hour. but in this case 7 fps works out to 4.772 miles per hour.
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Unread postAuthor: MrCrowley » Sat Nov 04, 2006 1:18 am

but wouldnt you be going .5mph? or .24444*yps?(not sure if thats right as i use metric and im pretty sure there is no such thing as yps(yards per second :lol: ))
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Unread postAuthor: SpudStuff » Sat Nov 04, 2006 2:49 am

Yes that sounds aproximently correct. Because ~1.5 FPS =1 MPH.
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Unread postAuthor: boilingleadbath » Sat Nov 04, 2006 4:59 pm

Well, nobody uses "yards per second", but it's still a valid unit.

Also acceptable, although somewhat eccentric:
furlongs per fortnight (200 yards / 14 days) [this is a classic]
anstroms per minute
inches per second [I've acctualy done calculations with this]
scotch_tape_thicknesses per simpsons_episode_13
meters per 3.33x10^-10 seconds [acctualy, not that ecentric]
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