It's common knowledge that light can produce chemical and electronic changes (photography is based on those effects); however, many people consider light to have no mechanical effect. Some are familiar with the novelty of a radiometer that spins when placed in the light. Fewer are aware that a cymbal will vibrate audibly if hit by the light from a camera flash.1 It came to our attention that the bubble in an ultra-sensitive level would move toward a flashlight beamed at the level from one end. Our investigations of this phenomenon show that it is thermal in nature and the effect large enough to be demonstrated in a classroom. With the addition of a small heating wire, the bubble level can be converted into a small heat engine.

1.
Antonio
Serrano
, “
Hearing a flash camera
,”
Phys. Teach.
43
,
309
(
May 2005
).
2.
The appendixes can be viewed online at http://dx.doi.org/10.1119/1.3670081. E-PHTEAH-50-013201.
3.
Ducourret SA, 11 Rue de Chenival - BP 29 - 95690 Nesles la Vallée, France; www.ducourret.com.
4.
Level Developments Ltd.
, Spencer Place, 97-99 Gloucester Rd., Croydon, Surrey, CRO 2DN, England; www.leveldevelopments.com.
5.
MSC Industrial Supply Co.
, 75 Maxess Rd., Melville, NY 11747-3151; www.mscdirect.com.

Supplementary Material

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