Joule’s Experiment

Mechanical work and thermal energy

James houle performed this experiment to show that the mechanical energy can be transformed into internal energy in water producing a rise in temperature.

The appratus used :

The structure :

Two heavy lead masses are attached to a string wounded around the spindle of an eight vanes paddle wheel.

Insulated copper vessel containig water including four fixed vanes to prevent the circulation of water (you will know why do we want to do so).

A thermometer to record the increase of temperature of water

The Experiment :

we wound the masses to the maximum height

when the masses fall freely , this leads to spining paddles(the potential energy stored in the masses is converted into kinetic energy in the paddles , i.e :the decrease in KE = increase in PE).

the turning paddles do work on water (churning it up)equal to force of gravity times L(the potential energy).

by the time the masses stop , all of the potential energy has been transfered to work in water (minus some friction in ropes).

the motion of paddle wheels cause friction between water molecules leading to an increase in the temperature of water.

the fixed vanes are used to increase the collisions between water molecules , because if water rotated uniformly , the water temperature won’t change much.