Demos: 3A-01 Expansion Lever

A long, thin brass rod, clamped at one end, is heated by a match or candle. The expansion of the rod is demonstrated by the turn of a small-diameter axle beneath the rod. The axle has a small mirror attached that reflects a laser beam onto the screen. This is essentially an optical lever so that the small expansion of the rod is magnified greatly through the moving spot on the screen.

Directions: Shine the laser beam onto the mirror and adjust the mirror to produce a spot relatively high on the screen. Using a match or candle, heat the rod by moving the heat source back and forth along the rod. The spot on the screen should move significantly. NOTE: There is always the possibility that the axle might get “stuck”, causing the rod to slide over it. Moving the axle slightly forward or back may prevent this.

Suggestions for Presentation: After presenting the concepts of linear expansion, point out that that the expansion is very small and essentially invisible to the naked eye. You might want to spend a little time explaining the principle of the optical lever and how this can magnify the expansion visually.

Applications: The axle suggests that if there is a problem with a beam or pipe expanding or contracting, it can be placed on rollers to avoid buckling.

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Last Updated: May 9, 2016 11:44 AM