Surely by now, someone online has clearly shown this image to be fake. Instead, let's use this as an example looking at the way people think about forces and motion.

I'm not exactly sure of the reasons someone would create a fake image. Maybe it is for attention or for amusement (I guess it is fun to trick people). But let's say you are the person creating this image. First you want to pick something that people have some experience with. How many of you have actually been on one of these spin-around-in-a-circle swing ride? I remember this ride as one of those rides you could get on and just chill out. If it was hot outside, the breeze always felt nice. They aren't even that scary. Actually, they can probably be scarier for parents watching their kids than for the kids themselves.

So the image faker now has a situation that people can relate to. All the image needs is to be modified to invoke an emotion.

Forces and Circular Motion ————————–

Suppose something is moving around in a circle. Maybe it is a amusement park swing. Here is a force diagram for one of the riders.

There are only two forces on the swinger. There is of course the gravitational force pulling down. The only other force is the tension in the chain pulling on the swinger in the direction of the chain. Then why does the swinger move in a circular path? A component of the tension force pulls up to counter act the gravitational force. The other part of the tension from the chain pulls towards the center of the circle. It is this part of the tension force that makes the swinger move in a circle.

If you like, you can break all forces into two types. If a force is in the same (or opposite) direction as the motion (velocity) of an object, that force will cause the speed to either increase or decrease. If the force is perpendicular to the direction of the velocity, this force will cause the object to change directions. Of course you can have a force that both speeds up an object and causes it to turn.

Really, that is it. That is the only physics that you need to get this swinger to move around in a circle. Sure, there is a relationship between the angle the swing is at and the speed that the swinger moves, but for now we can leave that alone.

What Would Really Happen? ————————-

If the chain suddenly breaks, what happens next? Well, the force diagram becomes a little bit simpler. It would just look like this:

This gravitational force would cause the velocity to change in the downward direction. So, clearly, it would fall down since before the chain broke it wasn't moving in the vertical direction at all. But what else would it do? Here is a diagram of the swinger from the top view.

In this view (after the chain broke), you can't see the only force pulling on the swinger - the gravitational force is pulling down. Since there aren't any forces pushing the swinger to the left or right, from the top the swinger would just go in a straight line.

In the faked image, the falling swinger is clearly moving away from the swing in a path perpendicular to the way he was originally moving.

Why Would a Faker Get This Wrong? ———————————

First, I will acknowledge the possibility that perhaps the artist make the error on purpose. Why? Perhaps the artist thought this was funny or even part of the artistic element of making a fake image. Another reason it could be wrong on purpose would be to make people accept the image as real. What? Did I just say that? Yes. Sometimes, if you create the picture correctly it will look odd to people. The same thing is true with the flying R2-D2 in Star Wars. No one questions the way he flies (except to question THAT he flies at all) because they made him fly in a manner consistent with the common incorrect ideas.

For the swing, many people seem to think that if an object is moving in a circle there is a force pushing outward from the center of the circle. This is the fabulous and mythical centrifugal force. Even though the centrifugal force is fake, it can still be useful in some ways. However, the point is that if you are in a stationary frame then there IS NO force pushing outward.

But if there WAS an outward pushing force, then what would happen when the chain breaks? I guess this outward pushing force would still be there but the chain would no longer be balancing this force. The conclusion of this line of thinking is that the swinger would shoot out directly away from the center of the circle.

You can try this yourself. Get a ball on a string and swing it around your head. Which way does the ball go when you let go of the string?