Does a horizontally spinning weight = no motion weight?

evowerks

OK. We seem to have a consensus that the scale would indeed read 100kg. I think the concept I was missing was that the spinning weight is not on the same plane as the center. (i.e. not horizontal) It makes sense that the weight can be transferred down to the scale given the vertical component of the string is still present. Thanks to all for the input.

J

Grizzled

Krrrhm, a small correction folks. I submit that if the scale in questison is properly constructed, it will register MORE than 100kg. You all forgot horizontal force applied to the scale!

What prevents that ball from flyng away? String tension. Where does THAT come from? Well, via the man and the soles of his feet, ultimately - it's friction with the scale surface. Spin that ball fast enough and it can pull you off the scale...together with your electric contraption :-)

So, if your scale can measure horizontal as well as vertical forces applied to it, the total will be more than 100. How much more - depends on rotation speed. The resulting force vector will be rotating around the vertical and the angle - how far off the vertical it is, also depends on the speed.

Drakkith

How does a horizontal force make a scale have a higher reading?

Grizzled

I thought I explained it above. In detail.

The platform the man stands on must compensate (with a spring, counterbalance, whatever) not just for the gravity but also for the inertia of that ball flying in a circle.

But really... I repeat myself.

sophiecentaur

Before starting on this thread, I think we ought to think (have thought) what the consequence would be if the two weights didn't 'add up'. If they didn't, then we would have the makings of a reaction-less propulsion system and that's how we would all be travelling about the planet these days. I don't see any craft of any type which work this way.
What you have to do is find reasons for this suggestion to be basically flawed rather than to try to kid yourself that it could be right. It all boils down to the forces acting on the whirling mass and the string. The vertical component will be the same (assuming we eliminate vibration by controlling the spin well enough) whatever rate the mass is whirling round. The centripetal force will be just enough to sustain the circular motion and the tension in the string will be the vector resultant of the centripetal force (H) and the weight force (V).
How could this thread possibly have extended to two pages, I wonder? It must be such an attractive idea that people actually want Physics not to apply.

Grizzled

More likely it's simply the way even elementary physics is [not] taught in schools today.

On the other hand, that's the propupsion UFOs use, haven't you heard?

Drakkith

Yes, but I don't see how that matters to a horizontal force. (Not saying it doesn't, I'm saying I don't know)

sophiecentaur

You haven't ever been abducted and 'probed', obviously.

sophiecentaur

The man and mass will mutually move about their mutual CM if they are decoupled from the platform of the scales (either by having frictionless shoes or by wiggling his bum appropriately to maintain no horizontal force on the platform - a-la hula hoop). In that case, there will be no H force on the scales.

evowerks

Since I started this thread I feel obligated to ask some of you guys to take a deep breath. I think it was a fair question worthy of asking and if you guys wish to debate how American high schools blow please do it elsewhere.