# Time change and degrees longitude

#### missrikku

The problem states:

Travelers reset their watches only when the time change is 1.0 h. How far, on avg, must you travel in degrees of longitude until your watch must be reset by 1.0 h.

I don't really understand what this question is asking for, but I attempted to "solve" this by keeping in mind that the Earth rotates 360 deg in 24 h.

This is what I tried:

x/360 = 1/24
24x = 360
x = 15 degrees

is 15 deg, the correct ans? if not, what exactly is this problem asking for and what associations should i make in order to solve it?

thanks!

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#### Tom Mattson

Staff Emeritus
Gold Member
Originally posted by missrikku
This is what I tried:

x/360 = 1/24
24x = 360
x = 15 degrees
That's a good try, but it is not quite right.

Travelers change time when passing to a new time zone. These zones were set up because of the rotation of the Earth, but they do not exaclty correspond to the Earth's rotation. To be more specific, there are 25 (not 24) time zones.

So, if one big time zone corresponds to 3600 then how many degrees do 25 time zones correspond to?

#### missrikku

ok, with your suggestion i did the following:

1 timezone / 360 degrees = 25 timezones / x
x = 9000 degrees

is this the distance? that sounds like great distance to reset your watch by 1.0 h!

#### Tom Mattson

Staff Emeritus
Gold Member
Oops, my fingers moved faster than my brain!

There are 25 time zones in 360 degrees, and there is 1 time zone in x degrees.

Sorry!

Staff Emeritus
Gold Member
Dearly Missed
That's not quite right. Most time zones are approximately 1 hour = 15 degrees wide. But for political reasons their boundaries do not exactly follow lines of longitude (in the US, for example, they tend to follow state boundaries). The extra time zone in the Pacific is identified by a 1/2 hour change. 15 degrees is right on the average, but to be absolutely correct you have to consult a map or globe with the zones marked.

#### Tom Mattson

Staff Emeritus
Gold Member
The extra time zone in the Pacific is identified by a 1/2 hour change.
Now that I didn't know.

#### HallsofIvy

Homework Helper
Ah, now that makes sense. I was wondering why in the world there would be 25 time zones instead of 24 and about to speak harshly to Tom.

However, having two "1/2 hour time zones" would make sense- and correspond to 24 "regular" one hour time zones. The original 15 degrees per hour change was correct.

#### physics247

If it is noon in New York, What time is it at the North Pole?

Several hours later, when it is noon in LA, now what time is it at the North Pole?

How many times a day is it noon at the North Pole?

How many days a year are there at the North Pole?

#### HallsofIvy

Homework Helper
This was a joke, right? Sometimes I have trouble telling.

#### physics247

Sometimes physics is phun(?)

The phun arises sometimes when standards don’t make sense - as in this case. All time zones converge at the north pole, so at the north pole it is any time you want it to be.

From the political viewpoint, one time zone is as valid as the next, although one may be more convenient than another for any particular group. It makes just as much sense to say that “noon” occurs at the same time at the north pole as in NY as it does to say it occurs at the same time as in LA. It would also “make sense” from this viewpoint to say that there are about 365.25 days per year at the north pole.

From a geophysical point of view none of the above makes sense. Noon occurs when the sun is at its highest point in the sky. At the poles, there is only one noon each year, there is only one dawn and one sunset each year. There is only one day per year at the poles.

What’s my point(s)? Mainly: we can get complacent about standards until we realize their limits ( or: measuring things can give us a false sense of security that can stand in the way of understanding); what is time?; what is “real?”.

Is it s joke? Not “really.” Is it phun? I hope so.

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