If you sit in a good swivel chair with your feet off the floor, the chair will turn slightly as you move about but will immediately stop moving when you do. Why can’t you make the chair spin without touching something?
To understand why a swivel chair stops spinning when you stop moving, we need to consider Newton's laws of motion. Newton's first law states that an object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force. In the case of a swivel chair, you provide the initial force by moving your body, which sets the chair in motion.
When you push against the floor with your feet, you create a force that propels the chair to spin. However, once you stop exerting force, there are no other forces acting on the chair to keep it in motion. The key point to understand is that the chair spins due to the conservation of angular momentum.
Angular momentum is a property of rotating objects and depends on both the rotational speed and the distribution of mass around the rotation axis. When you push off the floor, your body and the chair start rotating together due to the conservation of angular momentum. However, when you stop moving, there are no external torques acting on the chair, causing it to slow down and eventually come to a stop.
To sum it up, you cannot make the chair spin without touching something because it relies on the transfer of angular momentum from your body to the chair through the contact with the floor. Without this initial force or external torques, the chair will not continue spinning indefinitely.