Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Moving energy from one thing to another 1

Demonstration

This series of activities is designed to give students experience of energy transfers.

Apparatus and materials

G-clamps, 5 cm, 2

Malvern energy transfer kit (click on link to see what this includes)

Variable low-voltage power supply

Mass, 0.5 kg

Brick, single

Cord

Rubber band or driving belt

Health & Safety and Technical notes


The Malvern energy transfer kit is also available as individual components from Beecroft & Partners Ltd and other suppliers. Individual items may also be substituted for those in the kit.
 
All motors can be driven by up to 12 V and can also be used as dynamos. Do not allow the dynamo to labour under too heavy a load.

 

Procedure


a Using the brick to operate a dynamo and light a lamp.

using brick to operate dynamo and light lamp
 
Clamp the motor/dynamo unit to the bench with a G-clamp. Fix the line-shaft unit next to it. Tie the cord round the brick and wrap it round the axle of the line shaft.
 
Connect the output terminals of the dynamo to the lamp unit.
 
When the brick is released it will turn the dynamo which in turn lights the lamp, or several lamps in parallel.
 
b Using a battery to drive an electric motor

using battery to drive electric motor
 
Connect the motor to a 4-6 volt battery.
 
c Using an electric motor to lift a load which then drives a dynamo to light a lamp(s).

Clamp the motor/dynamo unit and the line shaft unit next to each other. Connect the pulleys on each with a rubber band or driving belt. Secure a cord to the axle of the line shaft and attach the lower end of the cord to a 1/2 kg mass. Connect a 4-6 volt DC supply to the motor/dynamo unit via a two-way switch. The switch is thrown so that it connects the power supply to the motor and the load is raised. When the switch is thrown back and the load allowed to fall, then the dynamo lights the lamps.
 
d Using the motor to drive a dynamo, which can light a lamp.
 
Clamp the motor and dynamo units next to each other and join their pulleys with the rubber band or driving belt. Connect the motor to the power supply and the dynamo unit to the lamps.

using motor to drive dynamo and light lamp

e Using the motor to drive a flywheel and the flywheel to drive the dynamo.

using motor to drive flywheel and dynamo

Clamp the flywheel next to the motor/dynamo unit. Connect the pulleys on each with a rubber band or driving belt. Connect the power supply to the motor via the two-way switch so that when the switch is thrown the motor turns the flywheel.
 
When the switch is thrown back the flywheel turns the dynamo and the lamps light.
 
f Using the water turbine to drive a dynamo, which lights a lamp. This requires practice.

using water to drive turbine to drive a dynamo, which lights a lamp

Position the turbine/pump unit next to the motor/dynamo unit and clamp both rigidly with G-clamps. Connect the pulleys on the two units with a rubber band or driving belt. Connect the output from the dynamo to a lamp unit with one lamp. The water from the mains enters the turbine at the top and the pressure drives round the turbine blades, which in turn drives the dynamo. If the water pressure is not very great, some form of force pump will be necessary to increase the pressure.
 
g Using a pump to raise water.

using pump to raise water

Clamp the motor/dynamo unit next to the turbine/pump unit, which in turn is clamped next to the head of water unit. Connect the pulleys on the motor and pump units with a rubber band or driving belt. Apply 4-6 volts d.c. to the motor. This will drive the pump unit which takes water from the lower level to the higher one. (It is necessary to prime the pump by filling with water before use: this is achieved by sucking on the third connection to the pump unit with a finger over the output and the input under water.)

 

Teaching notes


1 You can set up a selection of these activities as a circus so that groups of students can progress round them. At each station students record the main energy transfers, saying where the energy is to begin with, where it ends up and how it is transferred.
 
2 In step a energy is transferred from chemical energy (food and oxygen) stored in the muscles to uphill energy stored in the raised brick. When the brick falls the stored uphill energy is transferred to motion energy of the brick. When the brick hits the floor the motion energy is transferred to the floor warming it up. The floor and the surrounding air may be caused to vibrate and a sound will be heard too.
 
When the raised brick is connected to the motor/dynamo unit and allowed to fall then the lamp lights. The energy stored in the raised brick is transferred to the dynamo by the belt when the brick falls. The dynamo and an electric current carries energy to the filament of the lamp. The filament becomes hot and glows, radiating light to the surroundings.
 
In b the chemical energy stored in the battery is transferred by the electric current to the motor, causing the motor to have rotational kinetic (spin) energy.
 
In c the spin energy of the rotating motor is transferred by a belt to the line shaft, raising the load so the load gains uphill energy. When the load is allowed to fall, gravitational potential energy stored in the raised weight is transferred via the belt to the dynamo. The dynamo rotates and energy is carried by the electric current to the filament of the lamp, which warms up and radiates light to the surroundings.
 
In d energy is transferred to the motor from the power supply giving the motor spin energy which is carried by a belt to give the dynamo spin energy. The electric current then carries energy to the filament of the lamp, which gets hot and the lamp then radiates light to the surroundings.
 
In e energy is carried from the power supply to the motor, which causes the motor to have spin energy. This energy is then carried, by the belt, to the flywheel, which also gains spin energy. The spin energy stored in the flywheel can be carried by the belt to the dynamo which rotates. An electric current then carries energy to the filaments of the lamps, which get hot and radiate light to the surroundings.
 
In f water from a high reservoir (feeding the water main) or a pressurized water pump flows through the turbine, turning the turbine blades before flowing out of the system. Uphill energy stored in the water because the water reservoir is at a high level is transferred to rotation energy of the rotating turbine blades. The belt transfers this rotation energy to motion energy in the dynamo. A moving dynamo produces an electric current, which transfers the energy to the lamp filament. The lighted lamp radiates the energy to the surroundings.
 
This demonstration depends critically on the water pressure and the pressure may only be high enough to turn a small generator and drive a very slender elastic band. If the lamp will not light, it can be removed and replaced with an ammeter to show that there is a small current flowing.
 
In g an electric current transfers energy from the power station to the motor, which gains rotation energy. This energy is transferred by the belt to the pump so that the pump gains rotation energy too. Water can then be raised to a high level reservoir, so gaining uphill energy. This is the reverse of demonstration f.
 
3 Steps f and g model a pump-storage hydro-electric power station such as at Dinorwig. There is only enough water in the reservoir to operate for about 3 hours. When there is 'spare capacity on the grid' the water can be pumped back up to the reservoir. Power stations like this can be brought up to generating speed in a few seconds to cope with a dramatic rise in demand for electricity.
 
This experiment was safety-checked in November 2005.