How to convince your flat-earther friends that the earth is round

Illustration: Rhett Alleyne

We can see that there is a right triangle with a hypotenuse equal to the distance from the observer's eye to the center of the earth (R+h), the other two aspects are R and the distance to the horizon (s). Using the Pythagorean theorem, we can solve it as follows: s:

Illustration: Rhett Alleyne

Now, just assign the values. R and h The distance is 4,657 meters or approximately 4.69 miles. Of course, as the distance from the surface increases (h), you can also see further away. But if you stand on the shore of a lake and it's only three miles wide, you can't see the other side. Yes, because the earth is spherical.

swing the pendulum

This second experiment is a little more difficult to set up, but it doesn't require a huge lake. You need to hang a mass on the end of a string and rock the mass back and forth. That's right, it will be a simple pendulum. However, if you carefully release the pendulum (without giving it a circular motion), the pendulum will no longer just swing back and forth. Instead, the direction of the swing changes slowly. This is often called the Foucault pendulum (named after Leo Foucault).

Why does this happen? To make it more clear, let's consider this as an extreme case. Imagine there is a block hanging from a point just at the North Pole (assuming there is still ice there to stand on). As the pendulum swings back and forth, the Earth below it rotates (because the Earth's rotation causes day and night). Here's an animation (not real-time) showing what this looks like.

The pendulum is just swinging back and forth, but the Earth is rotating beneath it. This makes the pendulum appear to change direction as it rotates, but it takes half a day for the pendulum to swing back in its original direction (as seen from the North Pole). A complete cycle takes him one day.

wait a minute! This does not prove that the Earth is spherical. Maybe it just shows that the flat Earth is spinning like a record on a record player. OK, but what about this? If you take the same pendulum to the South Pole, the pendulum will also rotate, but in the opposite direction. Because when you stand at the South Pole, the pendulum swings completely upside down from the North Pole.

But you don't need to go to the North or South Pole to conduct this experiment. You can do it at home too. As the Earth rotates, the pendulum swings again in various directions, but it takes more than half a day to return to its original direction, and the time varies depending on latitude.