Friction of air normally called drag (or air resistance), it could be argued that gravity also takes effect in stopping the swing, if it was only drag the swing could stop ten feet in the air, and if it was just gravity it wouldn't stop due to the laws of mass and momentum. The drag reduces the momentum, therefore making the swing slow to a stop and gravity keeps it as close to the ground as possible.
That would have to be perpetual motion
a child pushing his little sister on a swing
gravity
Gravity must be overcome.
Yes but they will not make the object start, they will only work once the object is going and will keep the object going the same speed from when the unbalenced forces stop.
it will stop
Bludgeon your self
Friction
forces are useful because they stop or make things moving e.g.car crashes
You can stop coming over the top in golf swing by doing a lot of practice.
That would have to be perpetual motion
Probably the movement on a swing can be approximated by assuming that the magnitude of each swing will be a certain percentage of the previous swing (because of lost energy).
If you stop your baseball swing in the middle and the ball is not in the strike zone, an umpire will look at your wrists. If your wrists are "broken" it is a strike. That means the position of your wrists determine if you took a swing or not. If they are still in the same position as they normally are before you take a swing, you did not swing. If your wrists are in the position they would be in after you took a swing, you took a swing.
a child pushing his little sister on a swing
gravity
air resistance and friction in the bearings
Gravity must be overcome.