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### Finding Miles Per Hour

```
Date: 03/06/2002 at 20:21:44
From: joshua
Subject: RPM (How to find mph)

Let's say I'm going 64.2 rpm. How many mph am I going? How do you
solve it?
```

```
Date: 03/06/2002 at 21:26:21
From: Doctor Twe
Subject: Re: RPM (How to find mph)

Hi Joshua - thanks for writing to Dr. Math.

That depends on the size of your wheel(s). Suppose your tire is 28" in
diameter. Then the circumference is 28*pi inches, or about 88".

Assuming that there is no slippage, that means that the wheel is
moving 88" every time it makes one complete revolution. At 60 rpm,
that equals 60 * 88" = 5280" every minute.

Now we must convert inches per minute to miles per hour. There are 60
minutes per hour so:

5280 in.   60 min.   316,800 in.
-------- * ------- = -----------
1 min.     1 hr.       1 hr.

There are 12 inches per foot, so:

316,800 in.    1 ft.   26,400 ft.
----------- * ------ = ----------
1 hr.      12 in.      1 hr.

And finally, there are 5280 feet per mile, so:

26,400 ft.     1 mi.    5 mi.
---------- * -------- = -----
1 hr.     5280 ft.   1 hr.

So with a 26" diameter wheel (and no slippage), 60 rpm = 5 mph.

I hope this helps. If you have any more questions, write back.

- Doctor TWE, The Math Forum
http://mathforum.com/dr.math/
```
Associated Topics:
High School Conic Sections/Circles
High School Geometry
High School Practical Geometry
Middle School Conic Sections/Circles
Middle School Geometry
Middle School Terms/Units of Measurement

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