Date: Thu Nov 5 11:15:22 2009

Author: Zani, Gerald

Subject: Electron Orbitals for Hydrogen



Do you have a favorite graphic that your faculty use to show the electron orbital shapes for Hydrogen?

Something similar to this graphic:

But hopefully you use something a little better that you can share.

- jz

-----Original Message-----
From: [] On Behalf Of Zani, Gerald
Sent: Thursday, November 05, 2009 9:50 AM
Subject: Re: [tap-l] Windmill generator - Bicycle Generator

When the Bicycle generator demo was used in the sophomore E&M class on Wednesday one student who is on the cycling team pedaled the bike generator. He had the bank of parallel lamps glowing quite bright as he tried to output 1000 Watts. He was coincidently scheduled for his power try outs later that very same day so he didn't want to work himself for too long.

I asked him to bring his power meter and bike to the demo lab so I can make a video of him riding as we measure him with power meter and then have him use the bicycle generator to compare. - jz

-----Original Message-----
From: [] On Behalf Of Sam Sampere
Sent: Thursday, November 05, 2009 9:14 AM
To: ''
Subject: Re: [tap-l] Windmill generator - Bicycle Generator

I have 2 devices for measuring power on my bike, and both are VERY cool. A third and more expensive but likely more accurate power measuring device exists, but I'm a demo guy and cannot afford that one. I'll also describe that, too.

First, the Polar Power meter.

No matter what gear you are in, the length of the chain that's free, i.e. not wrapped around a gear, remains constant. When you pedal, you put tension on your chain. If you know the length and the mass of your chain, then you know the linear mass density. Pop in a sensor that measures the vibration frequency, and you have just done Melde's experiment! Cool, measure the frequency of vibration and you learn the tension in the chain.

There is a sensor mounted on the chain stay, the frame member that runs from the bottom bracket (the point of rotation of the crank) to the rear dropout (where the wheel connects). That magnetically measure the vibration frequency.

There is a sensor on the rear derailleur which measures the chain speed. Knowing the chain speed and tension allows you to calculate the power. P = T*v. Cool. Lots of filtering and averaging to get the power.

(2) Power tap. This device uses strain gauges to measure the force applied to a know radius in the rear hub of the bike wheel. Force * r = torque. I think that's all that needs to be said.

(3) Most expensive are the SRM power meters. This puts the strain gauges right into the crank. You measure the torque and you get out your power. This really measures your output power. What makes it through to the wheels after losses in the drive train, frame flex, etc. is unknown. The first two methods do not measure power into the pedals, but only after the mechanical losses in the drive train, etc.

Anyway, there's your primer on cycling power measuring devices. Costs - polar, about $700, Powertap, about $1000, and SRM, about $1500 for the basic model. From a physics point of view, I think Polar is way cooler, but less accurate.

My fluid trainer came with a power chart. The fluid unit dissipates energy by warming an oil by rotating an impeller, ahhhh, Joules experiment! The unit is calibrated at the factory by speed. So if I know my speed, which every cyclist does, then you can look up your power on a chart.


-----Original Message-----
From: [] On Behalf Of
Sent: Thursday, November 05, 2009 8:42 AM
Subject: Re: [tap-l] Windmill generator - Bicycle Generator


Were you using a Power Tap on a bike for the measurements? If you were
you might explain to everyone how those devices work. I think they're
very cool.


Quoting Sam Sampere :

> I can put out 1000 W for all of about 20s before I fall over panting
> like a baby‚?¶ I can go for 23:00 time at 300 W (about 25 mph on at
> TT bike).
> Sam