Determine Joule’s mechanical equivalent of heat (J) using a rotating friction calorimeter with suspended load and revolution counter, measuring the mechanical work done against friction (W) and the corresponding thermal heat absorbed (Q) by the calorimeter water system. Explore a virtual apparatus, collect readings and analyse a graph.
Ready for a virtual observation.
Adjust the apparatus, then take a reading.
Readings are generated by an ideal model. The diagram is schematic and is not to scale.
The teaching simulation models friction calorimetry under idealized thermal conditions with constant initial baseline temperature T_0 = 20.00 °C, constant drum radius r = 0.0500 m, suspended load mass M_load = 3.000 kg, and invariant system heat capacity C_sys = 118.48 cal K⁻¹. In physical experiments, convective and radiative heat losses to the ambient room during rotation (~3–8 min) cause the observed final temperature to fall below the adiabatic value, belt tension fluctuations and spring balance vibrations cause small work variations, friction between the axle bearings and support pillars dissipates a small fraction of work outside the water chamber, water evaporation through drum seals can cause minor latent heat cooling, and thermometer thermal response lag introduces slight peak temperature reading delays. The simulation evaluates mechanical work using W = 2π r M_load g N, where r = 0.0500 m is the drum radius, M_load = 3.000 kg is the suspended load, g = 9.80665 m s⁻² is gravitational acceleration, and N is the revolution count. Heat absorbed is evaluated using Q = C_sys (T_f − T_0) in calories, where C_sys = 118.48 cal K⁻¹ is the total thermal capacity (100.00 g water + 18.48 g water equivalent of the copper drum). Equilibrium temperatures are calculated using T_f = T_0 + W / (C_sys · J), with J = 4.1860 J cal⁻¹ and rounded to 0.01 °C to simulate precision laboratory thermometry. Ordinary least-squares regression of W against Q across five revolution settings yields the reported mechanical equivalent of heat.
A thin-walled, specularly turned electrolytic copper cylinder (outer diameter 100.0 mm, radius 50.0 mm) mounted upon a low-friction horizontal axle with thermal insulating phenolic couplings, driven at steady rotational speeds (100–200 RPM) by a variable-speed motor or geared hand crank.
A wide, flexible woven friction band wrapped 1.5 turns around the circumference of the drum, supporting a calibrated suspended load mass (M_load = 3.000 kg) on the descending side and anchored through an adjustable helical spring balance (measuring back-tension T_2) on the ascending side to maintain steady floating equilibrium.
A precision five-digit mechanical cyclometer directly geared to the rotating drum drive shaft to record the exact total number of revolutions N traversed during each experimental run with single-rotation resolution.
A sensitive mercury-in-glass thermometer graduated from 15 °C to 45 °C in 0.05 °C increments, inserted axially into the hollow interior of the drum through a water-tight seal to monitor water temperature before and after friction cycling.
Determine Joule’s mechanical equivalent of heat (J) using a rotating friction calorimeter with suspended load and revolution counter, measuring the mechanical work done against friction (W) and the corresponding thermal heat absorbed (Q) by the calorimeter water system. Suggested independent settings: 200.0, 400.0, 600.0, 800.0, 1000.0 rev.
Weigh the clean, dry copper drum to ±0.01 g on a laboratory analytical balance, recording its empty mass m_cal = 200.00 g. Add exactly 100.00 g of distilled water at room temperature. Seal the drum cap securely and remeasure the total mass to confirm the water charge.
Exact gravimetric measurement of the copper drum and water mass is essential to evaluate the total thermal heat capacity C_sys = m_w + W_cal in calories per kelvin.
Mount the filled drum onto the insulated drive axle. Wrap the woven friction belt 1.5 times around the copper drum circumference. Attach the 3.000 kg load mass to the free hanging tail and hook the opposing end to the upper spring balance. Verify that the belt tracks centrally without wandering off the drum edges.
Proper belt alignment ensures uniform interfacial contact pressure and prevents edge-rubbing against stationary frame components.
Insert the precision thermometer axially into the drum cavity. Rotate the drum slowly by hand for several turns to mix the internal water, allow the reading to stabilize, and record the initial baseline temperature T_0 = 20.00 °C. Reset the mechanical revolution counter to 00000.
Establishing a uniform baseline temperature guarantees that all subsequent thermal elevation originates exclusively from friction work during the timed run.
Start the drive motor or turn the hand crank smoothly, accelerating the drum to a steady speed of approximately 120 to 150 RPM. Observe that the friction between the spinning drum and belt lifts the 3.000 kg load slightly off the bench rest so that it floats in free dynamic equilibrium. Monitor the small residual tension T_2 on the spring balance.
Floating equilibrium confirms that the net tangential frictional force acting on the drum surface is exactly equal to the suspended weight F_f = M_load · g − T_2.
Continue rotating smoothly until the target number of revolutions N is attained (e.g., N = 200 revs). Immediately halt the rotation, disengage the belt, and gently agitate the water inside the drum by rocking the axle. Watch the thermometer meniscus rise through an optical magnifier and record the maximum equilibrium temperature T_f attained before cooling commences.
Recording the maximum temperature after thorough internal mixing captures the true adiabatic thermal plateau before environmental radiation dissipation occurs.
Allow the drum to cool back to ambient baseline temperature. Repeat the measurement across five distinct revolution settings (N = 200, 400, 600, 800, and 1000 revolutions). For each run, compute the mechanical work W = 2π r M_load g N in joules and the heat absorbed Q = C_sys (T_f − T_0) in calories. Plot W against Q and determine Joule’s constant J from the slope of the regression line.
Linear regression over multiple revolution settings eliminates single-trial zero offsets and provides a statistically rigorous determination of the mechanical equivalent of heat.
Points are your observations. The fit uses SI x and y values before display scaling.
| # | Revolutions N (rev) | Final temperature T_f (°C) | Heat absorbed Q (cal) | Mechanical work W (J) | Remove |
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