A frictionless system consists of a swing of given length and its massive rider, initially at rest. Is it possible for the rider to kick this system into its unforced natural frequency?
Umm.Originally posted by HallsofIvy
Without friction, so that all forces are internal, then "conservation of momentum" says that we cannot change the momentum of the system by inside forces.
Ie, a kid sitting on a swing.Originally posted by krab
We now have a compound pendulum....
That really doesn't make a lot of sense. It sounds like you are saying the starting conditions are no internal or external motion or forces. It will just sit there then. Newton's first law.Originally posted by Loren Booda
My question again: for a frictionless pendulum initially at rest, can any movement "within" the bob, now having ceased, have caused the pendulum to continue at its nonzero natural frequency? This holds for a compound or a simple pendulum.
Yes, and the answer is yes. A pendulum not under continuous force can swing at only one frequency: its natural frequency.Originally posted by Loren Booda
(You may have already answered this.)
Now try the same without friction - that was my contention.I as well as many other kids could manipulate the swing from a dead stop to full swing without their feet touching the ground.
Where is this friction you are talking about? Wind resistance? Its not enough to get you moving.Originally posted by Loren Booda
Doc Now try the same without friction - that was my contention.
Whereso on the SODA website?I couldn't get one swinging at the swing's frequency; only at the muscle's frequency.
You construct one using sodaconstructor. First Clearall, Then select Fixed mass, and place the pivot point of the pendulum. Now select Free mass and place it somewhere below. Now click Simulate instead of Construct, and the swing begins to swing. You'll have to set k very large. It is the spring constant between the pivot and the seat; there are no rigid connections. And set the damping to zero for frictionless swing. Now comes the fun part. Elaborate the lower mass with connections and muscles to be some facsimile of a person pumping.Originally posted by Loren Booda
I've seen something like it on cable TV where the the machines evolve. Very pleasing to the eye and visceral. Whereso on the SODA website?