photo credit: Richard Heeps Photography

How Things Work: Front and Rear Bicycle Brakes

The car in this photo (hi-res version) is "doing a wheelie." Note the big racing slicks on the rear wheels--the force of friction that the road exerts on the rear tires creates a torque that rotates the front end of the car upwards. The same effect limits the effectiveness of stopping a bicycle with the rear brakes alone, since in this case the torque rotates the rear of the bicycle upward (see How Things Work:  Front and Rear Bicycle Brakes by Lou Bloomfield). For photos of motorcycle wheelies, see the Wheelie King from the Motorcycle Hall of Fame Museum.

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Cold Metal

Visit Cold Metal for an Exploratorium activity on the science of heat. You'll make observations with your sense of touch and then interpret them.

To learn more, visit Thermal Conductivity, part of Phun Physics from the University of Virginia.

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image credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF; image source.

Spectra

This image (hi-res version) shows absorption lines in the sun's visible spectrum. To find out more, see Atomic Absorption and Emission Spectra.

Analysis of these lines determines the chemical composition of a star.  For an explanation of why the lines of calcium--rather than hydrogen--dominate the solar spectrum, go to "Analysis of absorption Lines" in Spectra, from the University of Illinois (the other sections are interesting, too).

Eames Office: Powers of Ten

To see the universe at different scales, from the most distant galaxies all the way down to subatomic particles, visit these sites:  
   CERN Powers of Ten
   Secret Universe: The Worlds Within by Molecular Expressions
   Powers of Ten by Charles and Ray Eames.
One of these sites shows the same image for six consecutive powers of ten. Can you find it? Do these six images make sense?