Accelerating Top?

You Wrote:

"The "wobble" energy must be converted into rotational energy."

Why must the "wobble" energy be converted into rotational energy? Here is the equation for precession

Where Omega-P is the Angular Velocity of Precession, L is the angular momentum, and tau is a torque applied perpendicular to the axis of rotation.

In the example you give, Tau is due to gravity, Precession is the wobble, and angular mommentum is the rpm of the top. Notice that if tau is constant, then Precession velocity increases as angular momentum decreases. This is why when a top slows, it wobbles more.

Of course, Tau isn't constant when you first spin a top. In order to spin a top, you have to pick it up and then drop it or apply downward pressure to it. When you do this, the top feels a varying torque. This varying torque results in a large precession. When the torque decreases and then becomes constant (equal to gravity), the top stablizes and the wobble decreases (since the torque is lower).

So I don't see why it would increase in angular momentum, or as you put it, Wobble energy converted into rotational energy.

What do you think?

Try this:

Put a piece of reflective tape on a top.Use a strobe meter to check the rpm of the top as it changes from wobble to stable.The rpm increases.Why?

Enlighten me please.I am a willing listener.

this is called conservation of angular momentum. These tops that speed up change their weight distribution progressively so the average distance of the center of moment of inertia gets less. That means the top must spin faster to keep the angular momentum constant.

A real world example it a spinning ballerna or skater. They start their spin with arms and 1 leg extanded from the center of spin on the other lag and as they draw their leg and arms to their center their spin goes up dramatically.

here are a few hundred of them

http://www.google.ca/search?hl=en&q=%22spinning+skater%22+%2Bmomentum&btnG=Search&meta=

The rpm of the wobble (precession) and there is the rpm of the top (spin). If you mean the rpm of the wobble, yes, it does increase, but the spin does not.

I understood that the center of gravity of the top lowers slightly and this draws the former top portion into being the bottom portion(with it's greater weight) and this also makes it speed up.

As you start it is is unstable and the top falls to one side and the rate of spin slows markedly(as you would expect with the weight at right engles to the axis) as the top falls down and becomes the point on which the top spins the rate of spin goes up and the wobbles goes away as we now have symmetrical rotation again. Then it slows and falls over and runs away

You wrote:

As you start it is is unstable and the top falls to one side and the rate of spin slows markedly(as you would expect with the weight at right engles to the axis) as the top falls down and becomes the point on which the top spins the rate of spin goes up and the wobbles goes away as we now have symmetrical rotation again.

No, it wobbles at first because the torque is varying, once the torque stablilizes to gravity (g), it settles into a stable spin until friction reduces it's speed so that it starts to precess again.

Think of it this way, if you start a top and drop it an inch, it will wobble. Spin a top at the same speed, but drop it 6 inches and it will wobble much more. The higher you drop the spinning top, the larger the change in the torque in the begining (number of g's the top feels), the more of a wobble it will start with. The spin of the top is the same through all of this, its the "wobble" and the "torque" that changes.

As I previously stated, try it with a strobe tach and watch the speed(rpm) increase as the wobble decreases.Then the speed slowly decreases and the wobble increases and continues to increase as the speed drops.Seeing is believing..for some.

It seems that the initial state you speak of can be modeled as 2 simultaneous rotating masses. The first that we are familiar with is the flywheel effect. The center of rotation being a line through the verticle axis of the top, like an axle. The mass of the top is equally distributed about this line. A circular orbit. A sine wave. The second rotating mass has as its axle a line parralel to gravity which intersects the first axle at some point along its length(NOT necesarily the point of the top). The weight of the top is not equally distributed about this line. Nearly the full mass(momentum) of the top is opposed only be the centripetal force that is the friction of the point of the top against the table. As this rotating vector approaches being paralel to the initial impulse, it excedes the resistance of friction and moves the point of the top resulting in an eliptical orbit, the wobble, like a lasoo. Early on, before the initial impulse has time to decay, the elipse is large, its foci are wide apart. The intersection of the 2 axis occurs at a point below the table surface. They are out of phase with each other. You essentially have one gyroscopic force trying to move another. The interaction tends to move them into phase. The axis intersection rises to the point of the top at the table surface at the same time as the elipse foci move toward each other, eventually becomming coincident with each other as well as coincident with the axis intersection. At this point the 2 gyroscopes have syncronized. The first has reached its maximum angular velocity at the cost of the eccentricity of the 2nd. This is the most efficient state. However the initial impulse continues to decay, the elipse foci continue to move past each other, now widening. Likewise the axis intersection continues to rise, now above the table. Eventually the axis intersection is above the center of mass of the top and the focii have moved out so far that in order to complete an orbit, the sides of the top touch the table ending the spin.

Or not. I just kind of made that up while watching TV. I tend to spew a lot of nonsense when that happens.

Another pebble in the pool:

If one is the only rider on a playground roundabout (accepting that many contributors to this forum are old enough to know better) one experiences significant forces as the roundabout turns, as the load is out of balance. Now, apply muscular effort to bring the load towards the centre of the roundabout, and the angular velocity of the roundabout increases.

Does that help?

BINGO! Thats it, in very simple terms, I might add.