how to convert fps into mph

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Sat May 12, 2007 12:42 pm

Freefall has been working at a job with intelligent adults too long, and has forgotten that the target market for this how-to article <i>actually exists</i>.

The fact that they may use this how-to reveals that they are too poorly educated, or have little enough practice thinking, that they did not realize that you could figure out the conversion factor through that dimensional analysis.

For these people, it is handy (although possibly detrimental to their education) to have a nice, handy, conversion factor they can multiply their fps by.

Personaly, I figure it out through one of 3 ways:
1) Using a conversion factor of 1.5 fps/mph
It's off by a few percent, but it's a really nice number to work with mentaly.
2) Using a conversion factor of 1.47 fps/mph
I didn't intentionaly memorize it, but it saves me a few keystrokes when I'm using a calculator.
3) Using the 5280/(60*60) bit
Most accurate, when you have a calculator.
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Thu May 17, 2007 7:58 am

well i suppose ing every body is smart enouph to get a chronograph and get the fps off that and some chronographs will even tell the mph peaple who make cannons should be smart enouph
to see how fast they go so you know where to shoot and not to and it dosent take much to learn there are just alot o peaple that are stupid
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Corporal 5
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Thu May 17, 2007 8:20 am

Grow up people - there is no need to argue. MPH isn't a commonly used spudding unit, so I don't see why we really have to be petty over conversion factor.

We don't work in terms of hours or miles - no spud will stay aloft for more than about 0.01 hours, and ranges don't extend to whole miles.

Can anyone note a time they absolutely had to use MPH as a spudding unit?
Ok, it might be neat to compare spud velocity to a car's speed (or something similar), but it's not truly necessary.

Sticking in fps and m/s is far more convient.

So what would be far more useful is explaining that there are 3.28 fps to 1 m/s, or .3048 m/s to 1 fps, because those consitute regularly used units.
Novacastrian: How about use whatever the heck you can get your hands on?
frankrede: Well then I guess it won't matter when you decide to drink bleach because your out of kool-aid.
...I'm sorry, but that made my year.
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Thu May 17, 2007 9:00 am

one key factor in going from feet per second to mph is you need to know the feet per second of the cannon first most peaple here dont even know the cannons fps thats why when they say oh this type of valve is faster how do they know have they actualy tested it or do they just think becuse they spent more money on the valve and it lookes cool it shoots farther and lets more air threw it mph ist needed your right its just a cool factor of conversion you can say oh wow it shoots faster than a car

just somthing to think about
most cannons will shoot faster than hand guns if constructed right a nine millemeter only shoots at 6oo feat per second i have bb guns at 1000 fps and a paint ball gun at 300 feet per second goes 200 miles an hour rouphly
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Thu Jun 14, 2007 10:39 pm

I remember in Teched we would always use this single number
if you were goin from fps to mph you would multiply fps by .6818 and get a close aproximation of the mph. to go from mph, you would divide instead
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Fri May 12, 2023 6:16 am

shud_b_rite wrote:
Fri May 11, 2007 12:00 am
Another method is go to google and type in the search bar "564 feet per second in mph"

Google is the best tool, it can convert just about anything you can think of
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Tue May 16, 2023 12:16 am

The point is to know how to solve problems (not just this problem) without resorting to magical numbers specific to only one problem, like 22/15.

Dimensional analysis is based on the most fundamental mathematical fact: you can multiply anything by "1" without changing the underlying amount. If you can do dimensional analysis you can solve probably half of all the math you will ever run into. And, it provides a check on if your answer is correct.

Conversion factors are all equal to 1.
5280 feet = 1 mile.
So divide both sides by 1 mile:
5280 feet / 1 mile =1 mile / 1 mile
cancel number and units
5280 feet / 1 mile =1
and of course, you cold have dived through by 5280 feet instead;
1 mile / 5280 feet = 1

60 seconds = 1 minute.
60seconds / 1 minute = 1

The only other thing you need to know is that units act just like numbers. (This is a major flaw in how math is taught. Math teachers ignore units.)

2*3 = 6
4/2 = 2
feet*seconds/seconds = feet

To convert 10,000 feet to miles you take your number of feet and multiply by 1:
10,000 feet * (1 mile/5280 feet) = 1.89 miles

Why 1 mile/5280 feet instead of the other possible value of "1" (5380 feet/1 mile)?

Because only the first one will cancel the units properly. And here you see how dimensional analysis helps you tell if your answer is correct. If I use the right units but wrong value of "1", I would get:
10,000 feet * (5280 feet/1 mile) = 52,800,000 feet*feet/mile
which is obviously wrong because the UNITS are wrong. I don't even need to have enough domain knowledge to recognize that 52.8 million is the wrong answer, the UNITS tell me the answer is not what I want.

So the only other part for this particular calculation is the time conversion. 3600 seconds = 1 hour. So "1" is either;
3600 seconds / 1 hour = 1
1 hour / 3600 seconds = 1

Plug one in and see if the units work. If not, then use the other "1".

This approach will help with lots of your spudgun math. What is the volume of a 2" diameter by 3' barrel? Again a dimensional analysis problem, in part, since it has inches and feet and you want a volume.

Pi*((2inch)*(ft/12inch)/2)^2 * 3 feet = 0.833 ft^3
The first part has both the calculation of the area of the barrel (in ft^2) and the conversion from inches to feet. Note that if you multiply out the units you get ft^3.
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