Simple experiment you can try on your own.

http://nerdist.com/8-reasons-we-know-the-earth-isnt-flat/

"...THE SAME OBJECTS MAKE DIFFERENT SHADOWS
Here’s one you can try at home. If the Earth were flat, you could drive two sticks into the ground at any place on Earth, and the shadows those sticks would make would be the same length. (Because the Sun is so far away from Earth, its incoming rays can be considered parallel).

Place a stick in the ground on a sunny day, then measure the length of the shadow. At the same time, call a friend who is at least a few miles away from you and tell them to do the same. The lengths you measure will be different! The curvature of a spherical Earth means that sun rays will hit each stick differently if they are far enough apart...."