The answer is centrifugal force. It's not an actual force though, rather, it's an apparent force.
For example, if a person X is on a rotating platform (such as the one in the video) that rotates at a constant angular speed, an external viewer will see X do a uniform movement. But X, while seeing himself as immobile in the carousel, will perceive a force that drags him out (the centrifugal force) that pulls him away from the center of the carousel, which is balanced by the constraint reaction (not sure how it translates into English). Anyway, the only actual force here is this last one, the other one is apparent.
In any case, this is really a basic explanation and if someone can help me improve it, it'd be great.
An example in real life is when you enter a bend while inside the car. If you turn right, the centrifugal force will pull you (the body) to the left. Again: the force doesn't exist, it's only apparent.