PASCO ET-8781 Equivalent of Heat Tube - Manual (Page 5)

Mechanical Equivalent of Heat Tube Model No. ET-8781
4 ®
Introduction
PASCO’s Mechanical Equivalent of Heat Tube (ET-8781) is used for demonstrating changes
in gravitational energy to thermal energy. While the energy conversion is occurring, students
can measure and observe the temperature change in real-time in a DataStudio display.
As the tube is turned over, the steel balls fall the length of the tube and strike the thin, metal
plate at one end. Fastened to the bottom of the metal plate is a fast-response thermistor for
continuously measuring the temperature of the plate. The thermistor can be directly plugged
into either a PASPORT Temperature Sensor or a ScienceWorkshop Thermistor Sensor.
Students can then use DataStudio to measure the temperature increase caused by the impact.
In addition, students can measure the mass of the falling balls and the distance over which
they fall to calculate the change in gravitational energy.
The Mechanical Equivalent of Heat Tube is typically used in conservation of energy studies.
The tube can also be used as an analogy for the “disappearance” of kinetic energy during a
collision.
Theory
m
b
= mass of the steel balls
m
p
= mass of the aluminum plate
c
b
=specific heat of the steel balls
c
p
=specific heat of the aluminum plate
T=change in the temperature
L=length of the tube
Q=thermal energy (heat)
PE= gravitational potential energy
Potential Energy
The change in gravitational potential energy of the balls as they fall a distance h is given by
PE=mgh. If the tube is held vertically at its center and rotated 180 degrees, the balls fall a
distance of L, the length of the tube. If the tube is then rotated back to the initial position, the
balls again fall a distance of L. Note that it is important that your hand stay at a constant
height during rotation. Thus, the balls fall a total distance of h=2L for each back and forth
rotation, and the total change in gravitational potential energy of the balls is
PE=m
b
g(2L) (1).
∆