Topic: hey physics guys...

[grumpy]

physics question....

How do I figure out the energy needed to spin a wheel?

I want to compare the HP/watts needed to spin rims of differing weights.
Note that I'm looking at rims specifically, so assume all else is constant.
Let's use easy numbers. Say:
Radius = 10cm
Weight A = 100g
Weight B = 200g

How do I do it?

Is it just a "simple" torque problem or does it matter that the mass in question is at the end of the radian?
It seems like the placement of the mass would make a difference because of the mechanical (dis)advantage if the weight being out at the end of a lever - or does that not apply with a wheel?

[Duke McDukiedook]

W = F(d)

[TwoTired]

You need a time factor.

To keep any wheel spinning steady state, you need only produce the power needed to overcome resistance (friction or air drag).

Usually, greater power is needed to CHANGE the present speed, from stopped to some rotational RPM, for example.  And, how fast you need to change the rotational speed, vs. the mass of the object.

As long as you provide more power than friction or air drag resistance, the rotational speed will increase.  How fast it increases will be determined by the mass and magnitude of the power over friction and drag factors.

[scottly]

Here ya go, Grump!

[grumpy]

Cool, I can work with that.

Question: V1 and V2 are expressed in feet or meters / sec. Does that mean the roll-out of the wheel? EG say the circumference = 1ft  and the wheel spins twice/sec then V = 2ft ??

[Duke McDukiedook]

V is the velocity in ft/s or m/s.
I assume it is talking about rotation velocity and not translation.

[scottly]

Cool, I can work with that.

Question: V1 and V2 are expressed in feet or meters / sec. Does that mean the roll-out of the wheel? EG say the circumference = 1ft  and the wheel spins twice/sec then V = 2ft ??

The circumference is determined by the mean radius; the average radius of the mass. Let's say you have a 19" rim. The mass will be centralized close to about 18.75" diameter, as an SWAG, so the ft per rev would be 4.9'. If you know how much a steel rim and an aluminum rim weigh, you can just start plugging in numbers. Whatever number you plug in for V1, double it for V2. The flywheel effect is linear.   

[grumpy]

roger.

this is good - I can mess w/ this all day & it'll look like I'm actually working at work.

[dusterdude]

This is interesting


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