Using an electric motor to raise a load
The transfer of energy through an electric motor to potential energy of a load.
Apparatus and materials
Switch unit (very useful to break circuit quickly)
Line shaft unit
Demonstration meter, 0 - 5 amp DC
Rubber band or driving belt
Mass, 1 kg
Power supply, 0-12 V
Health & Safety and Technical notes
The mass you select as the load must be suitable for the size of motor you have available.
a Clamp the motor unit next to the line shaft unit and connect their pulleys with a rubber band or driving belt. Secure a length of cord to the axle of the line shaft and attach the other end to the chosen mass. Connect the motor to the power supply in series with the demonstration meter.
b Read the ammeter when the load is being lifted and compare this with the reading obtained when the motor is running light (that is, when disconnected from the line shaft).
1 In this demonstration energy is transferred from the power supply to the motor by means of the electric current. The chemical store of the battery or the fuel in the power station is therefore transferred to kinetic energy in the motor which is then transferred, via the line shaft, to gravitational potential energy of the rising load.
2 The current increases as the load increases showing that more energy has to be transferred in order to raise greater loads. Even when the motor is running 'light' with no load connected to it, there is a continual supply of energy to it. You might ask students:
'Where does this energy get transferred to?'
It warms up the motor.
3 Energy transferred by the electric current, E = IVt
Potential energy gained by the rising load, E = mgh
If you measure these, it is very unlikely that the two will be equal enough to satisfy students because of the energy 'losses' in the system, but they could be used to measure the efficiency of the energy transferred.
= (mgh / IVt ) x 100%
This experiment was safety-checked in August 2007