# Simple riddle involving time travel

This is a simple one, but it's BTTF (Back to the Future) day, so I figured it was appropriate:

What goes a minute in four seconds?

• A really bad clock? Four regular clocks? :P
– Deusovi
Oct 21 '15 at 14:25
• Technical: <blahblah>relativity< /blahblah> Something to do with time dilation, time-travel, and relative velocities. Oct 21 '15 at 14:30
• The TARDIS? The Doctor? Oct 21 '15 at 14:42
• Something travelling at ~900 knots. Oct 21 '15 at 14:43
• "simple" and "time travel" are not known for going together well. Oct 21 '15 at 20:11

The

Earth rotates through one minute of arc every 4 seconds.

• Got it. I figured it'd be a pretty simple one, but it was fun to think about. Oct 21 '15 at 14:45
• Hmm... The title was somewhat misleading then. Where's the time-travel? Oct 21 '15 at 14:46
• @chaslyfromUK : That was intentional misdirection. However, the other answer I was intending and would have accepted was the Sun, which travels across the sky over a period of time. So: time, travel. Just not exactly time travel. Oct 21 '15 at 14:49
• @chaslyfromUK: well.. one travels four second ahead in time in that four second time lapse. Nothing fancy, one sec per sec speed, but it is time traveling :-) But you are correct. Too.
– user10179
Oct 21 '15 at 18:53
• @DarrelHoffman - By the way I liked the riddle and upvoted it. I just don't personally think misdirection is a good idea. I tried it myself on one of my first few questions and it just caused annoyance. I believe that, with a little extra thought, it is possible to make the title and clues accurate but not obvious. Oct 21 '15 at 19:04

The hour hand on a 24-hour clock.

There are 360 degrees in a circle and 60 minutes in a degree, so a minute is 1/360/60 = 1/21600 of a circle. The hour hand moves 1/24/60/60 = 1/86400 of a circle each second, so in 4 seconds it moves 4/86400 = 1/21600.

Note: If you say "earth", make sure to qualify that you are talking about its rotation with respect to the sun, since its rotation with respect to the stars is about 1/365 off of one full rotation each day.

• +1: Can't deny that this would also be correct, though not the intended answer. (I was thinking of the sun's position in the sky, which takes the relative rotation into account, but was planning to accept "earth" as well, since it depends on your point of reference.) Oct 21 '15 at 18:01
• Your equation isn't balanced, just a typo you might want to fix. 4/21600 != 1/21600. :) Oct 21 '15 at 20:04

There is no time travel involved.

The fastest cars in the world (not counting drag racers)

Because... (The math is pretty rough but I think it shows I'm on the right track)

"Minute" means "minute of arc" and not a unit of time
Diameter of Earth = 7,917.5 miles
Perimeter of Earth = 24,873.6 miles (I know it's not really a sphere)
One degree of arc = 69.1 miles
One minute of arc = 1.15 miles
Top speed of the Venom GT = 270 mph
Distance traveled by Venom GT in 15 seconds = 1.13 miles

• Ahhhhh! OP edited as I was answering. I was on the right track, though, for the original time of 15 seconds. Oct 21 '15 at 14:45
• Sorry about that. My original mistake was based on a rewording of the puzzle: "What goes fifteen minutes in a minute?" Which is the same thing, just multiplied. Oct 21 '15 at 14:46
• @EngineerToast, StackExchange sites: where you post as quickly as possible regardless of quality before ninja editing a correct answer (for the timestamp!) Oct 21 '15 at 16:07
• If you only care about longitude, any vehicle traveling slowly around the south pole could accomplish the same thing :) Oct 22 '15 at 15:59
• @acbabis Fair point, since the minute of arc here is in reference to the Earth's rotation. Oct 22 '15 at 17:02