4B60.00 MECHANICAL EQUIVALENT OF HEAT - JOULE'S METHOD

PURPOSE: To determine the mechanical equivalent of heat.

DESCRIPTION:  Mechanical work is performed on the outside of a water filled copper calorimeter by turning a crank and rotating the cylinder against the friction of rope held under tension that is wrapped around the cylinder.

Each turn of the crank requires a calculable amount of mechanical energy. This energy is converted into heat in the copper calorimeter raising the temperature. The mechanical equivalent of heat can be calculated using two measurements.  The cranking device has a counter to count the number of turns so you can continue to lecture while cranking.  Typically 100-150 turns are needed to give good results with better than ten percent error.

REFERENCES: Thomas B. Greenslade, Jr., Nineteenth-century measurements of the mechanical equivalent of heat, TPT 40, 243-248 (2002)

EQUIPMENT: Joule's apparatus for mechanical equivalent of heat, digital thermometer with mount, 5Kg mass, 10g mass, adjustable right angle clamp and holder, small beaker with 30 g water.

SET UP NOTES: Make four turns of string around the cylinder.