How can something like a ruler be straight when we live on a round planet?

Answer 1

Geometry is a theoretical concept, nothing in reality conforms to these shapes perfectly..
The earth is not round and the ruler is not straight. They are close enough for them to be described so.
I hope the question is asking how we can insure that a ruler is straight enough when most measuring relies on a reference point that is independent of the curvature of the earth, this is a more sensible question.
There are numerous ways to make a straight line, one of the oldest is to hang a string from a hook with a weight on the end, when it comes to rest you can measure your ruler against it, a string under tension between two points will form a straight line, another method is to use a hose with water in it, the levels at each end will always be level and is a way of measuring horizontal levels (This would theoretically create a ruler with the curvature of the earth but this would be lost within the error of measurement).
Modern methods would obviously use a Laser and this would be far more accurate and independent but not perfect.
If you think of it another way, take a very long ruler that is curved so it stretches round the world and joins itself. Chop up this ruler into one meter lengths. Any of these meter lengths would be perfectly usable as rulers as the degree of curvature over one meter is negligible.
Another thing to consider is that the curvature would be along the length and it is the curvature along the width that would effect the straightness of the line.

Answer 2

Njbritton, that is a VERY intelligent question. Consider an extremely long building (several miles long). The builders have to use 'plumb lines', to make sure the walls are perfectly upright, right? So, if they 'plumb line' one end of it, so that it is perfectly upright and do the same with the other wall, at the other end of the building, a couple of hundred miles away, the roof is going to be longer than the floor, innit? AND, that roof, which was measured with a huge 'ruler' (spirit level), will be "curved", just like the ruler, to fit the curvature of the planet and the gravity within in, innit?? Hope you follow this, it's really quite simple. All rulers and buildings, would eventually show their curvature, the longer they stretched over the Earth's surface.

Answer 3

Because the planet is so big that a small ruler can be made straight, and it will look so close to lining up with the curved earth that you can't tell the difference.

Answer 4

Why not? A ruler is straight and a ball is round. So what? That ball could be a regular basket ball or the Earth. Rulers and balls are just different things that don't control each other.

Answer 5

A ruler is short enough that its easy to make it straight (to reasonable accuracy) without running into any manufacturing problems.

I guess if you tried to make a ruler larger than a few miles in length it would be more difficult.

You'd probably have to cut a trench into the ground and level it out using surveying equipment. Then you could build a table on the levelled ground and as long as the legs were all cut to equal lengths you'd know it was good to go.

The ruler could then be made on that 'flat' surface and you could really be sure it was straight.

Good thing rulers are only a few 10s of cm long.

Answer 6

huh? that's like asking why are the roads straight when we live on a bended planet, right? first, let's get one thing straight. since grade school we've been taught to believe that the planet is round like a huge basketball. it was reinforced when the teacher had a globe on his/her desk (you know, the one with the continents, rivers, oceans on it?). know why it was displayed as a globe? 'cause it was cheaper & quicker to construct a globe rather than what it really is: egg-shaped/oval in fact. now, back to your question. our rulers are an invention by us. we see 'straight' so we constructed rulers or measuring devices for that reason. we'd have to walk something like over 33k miles before we bend around the planet & start walking back to where we began. i appreciate questions like this (from a 13 year old) but hopefully you won't take my word for it. check it out. have tv & hooked up to cable or satellite? the science channel, discovery, etc. all have wonderful shows on subjects like this. educated yourself about the world we live in, find out what makes it tick 'cause when we do, we also find out what makes us tick!

Answer 7

Some mean answers to a decent question.

Some above have it right:

Any line, no matter how straight it seems, will eventually curve. This is because space is curved. Rulers, sides of buildings, and all other finite lines can be assumed as straight due to the fact that they do not stretch to inifinity.

All straight lines are simply minute fractions, or facets on a curved surface.

Answer 8

How can something like air be a gas when we live on a solid planet? One detail does not rule out the other.

Rulers are artificial and made to be as straight as necessary. The planet is not perfectly round either- it is covered in mountains and valleys etc. Think about it.

Answer 9

Why should the ruler bend with the planet?
Why is my shirt yellow when I live in a red brick house?

Answer 10

We're so small it seems ruler straight - if you discount the hills. If a beetle is on a ball to it, you imagine the ball seems straight.