Mechanical Equivalent Of Heat Apparatus

Product Code: TD-8551A



This Mechanical Equivalent of Heat Appara­tus provides an updated version of one of Joule’s most important experiments, converting mechanical work to thermal energy.

Replacement Items:
Cylinder (TD-8582)
Brush (TD-8583)

How it Works

The apparatus is simple and accurate. Turn the crank to perform a measurable
amount of work. The crank turns an aluminum cylinder. A flat nylon rope is
wrapped several times around the cylinder. As the crank is turned, the friction
between the rope and the cylinder is just enough to support a mass hanging from
the other end of the rope. This ensures that the torque acting on the cylinder
is constant and measurable. A counter keeps track of the number of turns of the

The work required to turn the cylinder is converted to thermal
energy by the friction between the cylinder and the rope. The thermal energy is
measured by monitoring the temperature of the cylinder using the embedded
thermistor. The ratio between the work performed and the thermal energy produced
and transmitted to the cylinder determines the mechanical equivalent of heat.
With this apparatus, the equivalence of work and heat is easily established to
within 5%.


  • The base, cylinder, crank and counter with a built-in table clamp
  • 3.6 meters of flat nylon rope
  • A 1-gallon can that can be filled with a measured mass of sand or water (if 10 kg of laboratory masses are not available)
  • Laboratory manual including theory, step-by-step instructions and data tables


  • Crank Counter — Counts the number of turns on the handle.
  • Thermistor — Embedded in the cylinder, it has lower thermal mass
  • Durable Construction — Constructed primarily of steel and aluminum, there’s virtually nothing to break. The thermistor is protected in the cylinder.

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