Why earth looks always flat when it is round Yes, we can easily explain to all intelligent adults why the Earth looks flat, when it is actually round.
But my question is, how can we explain this fact, that the Earth is round, to those people who will not accept new data, which contradicts their knowledge, by providing them with some proper facts?
 A: Tell them to take a flight to the edge. And call us there when they reach it.
A: Think of a circle first. So if you look at the whole circle you see it as round. Now just zoom into a small part of that circle. Now you don't see the whole cricle any more. But still you see a curvature. Similarly you making the cirlce larger and look into the same point. When the circle get large the difference between one point and the next point looks (gets) lower. Now think in 1000 km scale 
A: If showing them a picture taken from space won't convince them, I doubt there is anything you can do about  it.
A: If the landscape in front of you and your sceptical 'other people' is very flat, some curvature is still perceptible (but only just). Standing at a higher vantage point will increase your ability to see the curvature. I see this regularly near where I live, as I drive to the top of an escarpment and look down at the very flat Vale of York. This effect will only increase as you go higher up. If you can get your sceptics to the top of any sort of mountain, they will see it for themselves, and measure it by holding a long (meter or longer) straight edge up to the horizon. Going up in a plane above 20000m should clinch it, but could be an expensive proof!
A: The simplest thing to do would be to point them to the sun and show a person that it's round. Also point out that how could  sun move below horizon if it was flat?  
And one thing more, you could achieve with a clock. Get a clock and travel 3000 miles and ask a person why did the sun rised later/sooner, while the clock is moving at constant speed.
A: Possible options


*

*Show them picture of earth (taken from space)

*If the guy believes in Mathematics , ask him to measure distance between two far separated points. ( The metric of sphere will serve the purpose and not the Euclidean one)

*Go for a straight nose tour along any direction till you come at the same point. ( nothing as such can happen in a flat space)

*There is a famous shadow and stick experiment.
A: Use Google Earth:


*

*Start at high zoom level at your location, or anywhere — so that Earth would actually feel flat, as it does normally

*Use middle mouse button to rotate camera to get view parallel to Earth or similar

*Gradually zoom out showing how the curvature becomes more and more apparent as you go deeper to space

*Finally you are looking at the Earth from space. Now let the person you're trying to convince rotate it and play with it in other ways.


After that show several images of the Earth taken from space to confirm that what one sees in Google Earth is what the astronauts see.
A: Fly in a plane with that person. With enough fuel one day you guys shall reach at where you had started. This will prove that earth is round.  
Response to comments:
All material objects apply the gravitational force on all other material objects. The earth is made up of atoms,molecules etc, all these constituent particles exert force on each other.  
All the heavenly bodies in the universe are more or less spherical in shape. This is due to the fact that any material object of a given mass has least surface area if it is spherical in shape, lesser the surface area lesser the potential energy more the system becomes stable. So for a given mass the object tends to become spherical in shape.  
What would happen if earth becomes cylindrical?
Then all the objects placed on the curved surface of the cylinder near the  edge will fall towards the centre until the Earth becomes spherical because of the gravity. In fact every system tends to go from higher potential to lower potential state.   
Why some meteorites are not of spherical shape?
This is only the case for meteorites of small size. As the size grows the meteorites becomes  more an and spherical. The small sized physical objects does not have enough gravity to change their shape.
A: Simple, empirical questions to ask a person who believes the earth is flat:


*

*If the earth is flat, there must be countries that live on the edge,
literally. In this day and age, why haven't we seen any videos from
these spectacular sites?

*Why haven't we heard of any accidents where
a person got drunk and fell off the edge? Better yet: would such a
person actually fall off? Where does the attractive force keeping us
on the ground come from according to you? If it comes from the plane
that is the earth in your view, would they not simply swivel down and
end up on the other side of the earth? But then we would have heard stories from such people, going over the edge and coming back.

*Also: why do we have
oceans? If there were an edge, the water would flow off the edge and soon all be gone (or transfer violently to the other side of the earth). We don't see this happening either.


I wouldn't bring in things like the rotation of the earth or photographs from space because it's easy to dismiss things like that. Any argument you give yourself is probably easy to dismiss for such people. However, when you ask the right questions, they might come to the understanding that they can't satisfactorily answer them. They might experience that "hey, I hadn't thought of that!"-feeling.
A: Show them a lunar eclipse. A flat earth would not always cast a round shadow on the moon.
