# How fast does light travel in 1 ft?

1. Aug 7, 2007

### dan001

Hello everyone,

I was wondering if anyone could help solve my problem...

...How much time in seconds (or milleseconds) would light travel in 1ft? (assuming that it was traveling in a vacuum.)

I spent 2 and a half hours yesterday trying to solve this problem, but without much luck. I remember back in school, I would know how to do this kind of stuff, but now...well, you know.

If anyone knows the answer to this problem (and if possible, a formula), I would much apreciate it.

2. Aug 7, 2007

### cesiumfrog

speed = distance / time. Use google calculator. Welcome to PF.

3. Aug 7, 2007

### Gokul43201

Staff Emeritus
How much time to cover 300,000,000 meters (that's about 1,000,000,000 ft)? So, how much time to cover 1 ft?

4. Aug 8, 2007

### dan001

Wow, I don't believe how I could forget something so simple.

Thanks anyways for reminding me.

5. Aug 8, 2007

### robphy

um... wait, gimme just a ....

6. Aug 8, 2007

### neutrino

...and a teeny, tiny bit more. :tongue2:

7. Aug 8, 2007

### mgb_phys

Light travels at 1 foot / atto-fortnight, everyone knows that.

8. Aug 8, 2007

### Feldoh

You are a nerd among nerds :rofl:

9. Aug 8, 2007

### mgb_phys

No, a real nerd uses c = 1.8 terafurlongs per fortnight

10. Aug 8, 2007

### HallsofIvy

Staff Emeritus
And watch them ponys run!

11. Aug 8, 2007

### Dick

Um, what's that in planck units?

12. Aug 8, 2007

### mgb_phys

That would be a good homework question, what is planck's constant in the furlong/firkin/fortnight system.

13. Aug 8, 2007

### Dick

Mines a trick question. In planck units c=1, hbar=1 and G=1. Yours is harder. What's the mass unit in the firkin system? Stones, right?

14. Aug 9, 2007

### robphy

Using dimensional analysis,
h is in Joule-seconds or kg*(m/s)^2*s = kg*m^2/s

Although http://en.wikipedia.org/wiki/FFF_System says that firkin is a mass,
However, since it is used with water (whose density is about 1000 kg/m^3), we have an expression for the mass in kg of a firkin of water http://www.google.com/search?q=kg+in+firkin*(1000+kg/m^3)

So, since google has a problem with numerical constants in the unit conversion,

h / 1 000 = 4.8405995 × 10-34 (firkin * (kg / (m^3)) * (furlong^2)) / fortnight

or
h = 4.8405995 × 10^(-34) (firkin of water) * (furlong^2) / fortnight