Balanced Forces
Above is an image of the forces acting on a dancer when she is stationary. There are only two forces acting, support force and weight. As you can see, the two forces are equal/balanced, which means the dancer has no net force, (net force is the force left over after you take the smaller force away from the larger force) and so she is not moving at all in any direction. The weight force acting on the dancer is the gravitational pull of the earth, and the support force is the force that stops the weight from pulling the dancer down into the earth. In all stationary objects these two forces are balanced, and these two forces are present in all objects on earth.
Should the support force become more than the weight force, then the two forces will be unbalanced, and the dancer will have a net force in an upwards direction, which would cause her to move upwards. If the weight was (for some reason) more than the support force, then the unbalanced forces would cause the dancer to sink into the earth (or fall through the floor).
When the dancer begins to move, two more forces are applied, thrust and friction. The thrust is what causes the dancer to move forwards, and accelerate, and the friction is what causes the dancer to decelerate and stop moving. The thrust and friction are equal when the dancer is moving at a constant speed.
Should the support force become more than the weight force, then the two forces will be unbalanced, and the dancer will have a net force in an upwards direction, which would cause her to move upwards. If the weight was (for some reason) more than the support force, then the unbalanced forces would cause the dancer to sink into the earth (or fall through the floor).
When the dancer begins to move, two more forces are applied, thrust and friction. The thrust is what causes the dancer to move forwards, and accelerate, and the friction is what causes the dancer to decelerate and stop moving. The thrust and friction are equal when the dancer is moving at a constant speed.