Quick demonstrations and activities

Practical Activity for 11-14 14-16 16-19

The activities in this collection are all easy to set up, require minimal kit and will take less than 20 minutes to run. They have been created to support purposeful, frequent and varied practical science in schools as recommended by the Gatsby Charitable Foundation.

Power
Energy and Thermal Physics

Kettle power

Classroom Activity for 14-16

In this demonstration students predict which kettle boils first. You can use it to illustrate that power is the rate at which energy is transferred and to introduce the relationship P = IV.

Equipment

  • 3 kW electric kettle
  • Small low-power electric kettle (eg 1 kW travel kettle of type found in hotel rooms)
  • 2 plug-in energy meters with voltage, current and power functions
  • 500 ml measuring jug or beaker
  • Thermometer (optional)

Preparation

A 3 kW kettle draws a large current. Don’t use an extension lead. Plug each kettle into its own wall outlet and check that the RCD circuits in your lab do not trip when you switch on both at the same time.

The energy functions on your meters are likely to be calibrated in kilowatt-hours. They are not needed for this activity. If you do decide to use them remember to reset meters to zero before you start and explain how to convert to joules (1 kWh = 3 600 000 J).

Procedure

  1. Plug the large kettle into a power meter and into the mains supply. Do the same for the small kettle.
  2. Set both meters to the voltage function and note values on board. They should see that both kettles give the same reading (240 V).
  3. Pour 0.5 litre of water into each kettle. Measure water temperature (optional).
  4. Switch on both kettles at the same time.
  5. Switch both meters to the current function and note values on board.
  6. Switch to the power settings and leave both kettles switched on.

Discussion prompts

  • Which kettle will boil first?
  • The kettles are plugged into the same mains supply. Which kettle transfers energy to the water more quickly?
  • Can you see a relationship between power, current and voltage?

Teaching notes

Students may think that the smaller kettle will come to the boil first because there is less casing material to warm. Remind them that inside there is a large mass of water. It is not possible to work out which kettle will boil first from its appearance alone.

The mass of water poured into each kettle is the same. The starting temperature for the water is also the same and so is the end temperature because both kettles switch off automatically when the water reaches 100°C. The energy required to raise the temperature of the water in each kettle is equal.

The power reading in watts is the energy in joules transferred electrically in one second by the heating element circuit. For the small kettle the rate is about 1,000 joules per second. For large the kettle it is close to 3,000 joules per second.

The current readings reveal the reason that the larger kettle will warm up more quickly. The current is three times as great and so energy is transferred at three times the rate. We’d expect the kettle with a 3 kW heating element to boil about three times as fast as one with a 1 kW element.

Explain that the electrical power depends on both voltage (ie energy transferred per charge) and current. Multiply current (I) and voltage (V) to introduce the relationship for electrical power (P). Show that P = IV for both kettles.

If students ask why the larger kettle has a higher current, calculate resistances by dividing voltage by current. The large kettle’s heating element has a lower resistance and so for the same ‘push’ (voltage) from the mains the current inside it will be larger.

Learning outcome

Students define power as the rate at which energy is transferred and can use the relationship P = IV to calculate power for an electrical appliance.

This experiment was safety-checked in March 2020.

Electrical Circuit
Electricity and Magnetism

Quick parallels

Practical Activity for 11-14

This activity allows students to investigate up to three bulbs without them having to rebuild their circuit. You can use it to test their understanding of current in parallel circuits.

Equipment

Each group of students will need:

  • Low voltage power supply (e.g. 1.5 V electrical cell)
  • Three identical bulbs
  • Two ammeters
  • Eight 4 mm leads
  • Glass of drinking water and straws (optional)

Preparation

Before the start of the lesson, set up one circuit as an exemplar so students can refer to it if required.

Drinking water through straws is a useful analogy for parallel circuits, but students should not eat or drink in labs. Only provide straws if you carry out the activity in a classroom.

Procedure

Ask the students to:

  1. Set up the circuit below. To start only one bulb should be lit.
  2. Record the readings on both ammeters (A1 and A2).
  3. Predict what will happen when they connect lead Y.
  4. Connect lead Y and record observations.
  5. Repeat for lead Z.

Discussion prompts

  • Why must the ammeter readings always be the same?
  • Why do they go up when you connect leads Y and Z?

Teaching notes

Most students should be able explain why the readings on the ammeters are the same. The meters show the rate at which charges flow in and out of the cell. The two values must be the same because charge isn’t used up in a circuit.

For students that struggle to explain why readings increase when they connect leads Y and Z, a useful analogy is drinking water through straws. Adding more bulbs in parallel is like increasing the number of straws: the overall rate of flow increases because there are more parallel paths along which the flow can happen.

Learning outcome

Students predict and explain how the current will change when two or more bulbs are connected in parallel.

This experiment was safety-checked in March 2020.

Sound Wave
Light Sound and Waves

Slink-o-scope

Practical Activity for 14-16

In this demonstration students see how a longitudinal wave can generate a sine-shaped curve. You can use it to introduce sound displays on an oscilloscope.

Equipment

  • Slinky spring
  • Metre rule
  • Rubber band
  • Clamp stand
  • Felt tip pen
  • Sticky tape
  • A few sheet of A3 squared or graph paper (eg made by sticking two A4 sheets together)
  • Stopwatch (optional)

Preparation & safety

Building and testing your slink-o-scope will take about 10 minutes. For instructions, watch the video above.

In this activity there is no need for precise timing. The student in charge of timing can use a stopwatch or count (eg “one thousand, two thousand..”) to estimate how long it took to plot the graph.

Procedure

  1. Ask for two volunteers, one to be your assistant that holds the paper under the pen and the second to be in charge of timing.
  2. Holding one end of the slinky in place move the other end back and forth to generate longitudinal waves. The pen will move on the paper.
  3. Show the resulting graph to the class - they should see that that it is close to a straight-line.
  4. Place a new sheet of paper under the pen.
  5. Send longitudinal waves down the slinky again. Ask the timing volunteer to shout “start” so that your assistant can start moving the paper at a steady speed in a straight line towards the clamp stand.
  6. Ask the assistant to stop when they near the end of the paper and to shout “stop”.
  7. Display the resulting trace to the class – they should see a curve with a shape close to a sine wave.

Discussion prompts

  • What labels should I use for the axes?
  • What does the distance between two peaks show?
  • How can I work out the frequency?

Teaching notes

To identify labels for axes encourage them to think about what caused the motion of the pen across the paper. The movement in the vertical axis is driven by the slinky coil. In the horizontal direction the paper was pushed at a steady speed. It’s a displacement-time graph and so the distance between two peaks on the graph represents the time period T.

Show how to estimate the frequency f by finding the average for T over a number of oscillations. For example, the graph in the video above took 6s to plot and has 12 peaks. So T = 6/12 = 0.5 s and f = 1/0.5 = 2 Hz.

Introduce oscilloscopes as electronic equivalents of slink-o-scopes. Explain that switching on the oscilloscope’s time-base is comparable to asking the assistant to push the paper, connecting a microphone is similar to slotting the meter rule between the slinky coils and an incoming sound wave is like a longitudinal wave on a slinky. Provide an example of a sound trace and explain that the time period can be found by counting the number of squares between two peaks and multiplying it by the time base setting in seconds per division (s/div).

Learning outcome

Students determine the frequency of a sound wave from an oscilloscope trace.

This experiment was safety-checked in March 2020.

Sound Wave
Light Sound and Waves

Dancing sprinkles

Practical Activity for 11-14

This activity shows that a loud sound is capable of making small grains jump. You can use it to introduce the idea that sound is a vibration of the air.

Equipment

Each group of students will need:

  • Bowl
  • Cling film
  • Hundreds and thousands sprinkles of the type used for cake decorations
  • Large spoon or drumstick
  • Metal baking tray, drum or similar to hit to make a loud noise

Procedure

Ask the students to:

  1. Cover the top of the bowl with cling film. Stretch it tightly.
  2. Scatter some of the hundreds and thousands sprinkles on the cling film.
  3. Hold the baking tray close to – but not touching - the cling film and strike it sharply with the spoon.

Discussion prompts

  • Why does the baking tray make a sound?
  • How do the sprinkles move when they haven’t been touched by anything?

Teaching notes

Students will probably have heard of a ‘sound wave’ but, based on everyday experience (e.g. shouting or whistling), think it involves air travelling en masse from source to detector. In this activity there is no obvious source of moving air. Identify the source, medium and detector in your explanation and introduce the idea that a sound is a vibration of the air.

The baking tray is a sound source because it vibrates when it’s struck. The vibrations are transmitted through the air (the medium) to the bowl and cling film (the detector). The incoming sound wave makes the surface of the cling film move up and down and the sprinkles on its surface dance in response.

Learning outcome

Students describe sound waves as vibrations of the air, initiated by the vibrating source of the sound.

This experiment was safety-checked in March 2020.

Phase Change
Properties of Matter

Ice-water-oil

Practical Activity for 11-14

In this demonstration students observe oil floating on water and ice floating on oil. You can use it to test understanding of density.

Equipment

  • Two 50 ml measuring cylinders
  • 250ml beaker
  • Two electronic balances (capable of measuring to nearest g or better)
  • 400 ml vegetable oil
  • Water in a glass or clear plastic jug (at least 100 ml)
  • Blue food colouring
  • Ice cube tray
  • Tissues (to mop up any spillages)

Preparation

The night before the activity prepare blue ice cubes by adding a few drops of food colouring to water in an ice-cube tray and freezing. The blue food dye will make it easier for the students to distinguish the ice and resulting meltwater from the oil.

When carrying out the activity avoid getting oil on the bench or floor where it may cause a slipping hazard. Afterwards, dispose of the oil in the non-recycling waste by putting an absorbent material (e.g. newspaper or cat litter) into a strong bin bag and pouring the top layer of oil from the cylinders and beaker into the bag. The remaining coloured water can be washed down the sink with the tap running.

Procedure

  1. Add a few drops of blue colouring into the water in the jug.
  2. Pour 40 ml of the blue water into a measuring cylinder and add 10 ml of oil.
  3. Pour 40 ml of oil into the other measuring cylinder and add 10 ml of blue water.
  4. Put the beaker on a balance and zero it.
  5. Pour in the remainder of the oil into the beaker and add the ice cube.

Discussion prompts

  • The total volumes of liquid in each cylinder are the same. Are the masses?
  • When the ice in the beaker melts what will happen?

Teaching notes

Students may talk about ice and water being lighter or heavier than oil. Encourage them to think in terms of the density of these materials. Some may think that the mass or volume of an individual ice cube is important, show them this isn’t the case by floating both large and small ones in the beaker.

In both measuring cylinders the water settles at the bottom because it has a higher density than oil. The oil-water mixtures have the same volume, but the one with a greater percentage of water will have the larger mass because water contributes more mass per volume than oil. Confirm this by putting each measuring cylinder in turn on a balance (the mass difference should be about 3g).

The ice floats on the oil because it’s less dense than oil. When it melts, it turns to water and so we would expect it to sink. If they look at the beaker, they can confirm this. Blue water droplets are detaching from the bottom of the ice cube, dropping through the oil and collecting at the bottom of the beaker (if the ice cubes haven’t started melting use a ruler to submerge them to speed up the process).

During the change of state the mass doesn’t change (the reading on the balance under the beaker remains constant). The increase in density must be due to a decrease in volume. The molecules must pack more closely together when the ice melts (water is very unusual in this regard as most solid substances are denser than when they’re liquid).

Learning outcome

Students describe density changes during a change of state in terms of a rearrangement of the molecules.

This experiment was safety-checked in March 2020.

Force
Forces and Motion

Static crate

Practical Activity for 14-16

In this activity students observe a crate being lifted by two different methods. You can use it to introduce horizontal and vertical force components.

Equipment

  • Crate filled with books (or other objects) to provide a total mass of approx. 2.5 kg
  • Two lengths of rope each about 2 m long

Preparation & safety

Before the activity attach a length of rope to each end of the crate. Ensure that the ropes are tied securely and that the crate doesn’t tip over when lifted. During the demonstration discourage volunteers from trying to impress their classmates by pulling on the ropes with exaggerated force.

Procedure

  1. Tuck the ropes into the crate and use your hands to lift it off the floor or bench.
  2. Hold crate stationary with your arms straight and then put it down.
  3. Ask for two volunteers to pull on the ropes to lift the crate and hold it stationary above the ground with the ropes at angles of about 45°.
  4. Now challenge them to try to pull firmly on the ropes until they are horizontal.

Discussion prompts

  • Which forces act on the crate?
  • Are the forces balanced?
  • Why is it impossible to get the ropes horizontal?

Teaching notes

Most students should be able to identify forces acting on the crate lifted by hand and explain why they balance. The forces are vertical. Each hand provides half the upward force required to balance the pull of gravity.

For the crate lifted by ropes some may struggle with the direction of the lifting forces. Explain how they arise. When the crate is lifted off the ground, the ropes stretch slightly, exerting forces along their length and at an angle of 45°.

To explain how the forces balance, introduce force components. They can think of each force as being made up of two parts one sideways and one upwards known as the horizontal and vertical components. In the horizontal direction the components are of equal size but in opposite directions and so cancel each other out. Similarly, gravity is balanced by the vertical components.

No matter how hard your students pull, it’s impossible to get the ropes completely horizontal because you always need a vertical component to balance gravity.

Learning outcome

Students explain equilibrium situations in terms of vertical and horizontal force components.

This experiment was safety-checked in March 2020.

Gravitational Force (Weight)
Forces and Motion

Steady spoon

Classroom Activity for 11-14

In this class activity students balance a ruler and a wooden spoon. You can use it to introduce the idea of centre of gravity.

Equipment

Each group of students will need:

  • Wooden spoon
  • 30 cm ruler
  • Electronic balance (capable of measuring to nearest g or better)

You will also need:

  • A saw
  • Masking tape

Preparation & safety

Choose identical spoons with an oval-shaped bowl and cylindrical handle. Check that each spoon balances at a point on its handle.

Cut through each spoon at its balance point. Connect the handle and bowl together again using masking tape to make a spoon once more.

Procedure

Ask students to:

  1. Use their outstretched finger as a pivot to find the balance point of the ruler.
  2. Repeat for the spoon.
  3. Take the masking tape off the spoon and balance each part of the spoon separately.
  4. Measure distances from balance positions to the cut edge for both handle and bowl sections.

Discussion prompts

  • Why does the ruler balance at its midpoint, but not the spoon?
  • How does the mass left and right of the pivot compare?
  • Where should I draw gravity force arrows on a diagram?

Teaching notes

Students will accept that a ruler balances at its midpoint because it has a uniform shape. The mass left and right of the pivot is equal. Gravity pulls downs on each side with equal effect.

Students may suggest drawing one, two or many arrows to represent the pull of gravity on the spoon or the ruler. Encourage the discussion. The number of arrows depends on how we think of an object: a single entity, two sections or many stuck together. In principle we could draw small arrows for each of the many atoms that make it up. Introduce the term ‘centre of gravity’ as the point where we should draw a single arrow to represent the gravitational pull on the whole.

Experimentally, the centre of gravity position can be found by finding the point at which an object balances. If the handle has half the mass of the bowl, its centre of gravity must be twice as far from the balance point. More generally, for both bowl and handle, multiply mass by distance to show that these are equal either side of the pivot for the spoon.

Learning outcome

Students can explain why the centre of gravity of an irregular object is not half way along its length.

This experiment was safety-checked in March 2020.

Gravitational Force (Weight)
Forces and Motion

Toppling bottles

Classroom Activity for 11-14

In this class activity students tilt three bottles to see which one topples first. You can use it to introduce the idea of stability.

Equipment

Each group of students will need:

  • 3 identical small clear plastic bottles with caps
  • Beaker with at least twice the capacity of one of the bottles
  • Enough coloured water (use food colouring) to fill two bottles
  • Thick cardboard
  • Pencil
  • Sticky tape
  • Protractor (optional)

Preparation & safety

Using coloured liquid makes it easier for students to see the mass distribution for the bottles. Add a drop of food colouring to a beaker of water for each group of students.

Try to find bottles with flat bases so there is less ambiguity about the area of the bottle in contact with the board.

Procedure

Ask students to:

  1. Fill one bottle with coloured water to the very top.
  2. Half-fill another bottle (leaving the last one empty).
  3. Using sticky tape, secure the pencil to one end of the cardboard to make a lip.
  4. Place the three bottles in a row in increasing mass order along the board next to the lip.
  5. Raise the other side of the board slowly.

Discussion prompts

  • What force makes a bottle fall over?
  • Can you predict the order in which the bottles will topple?
  • Why is the middle bottle the most stable?

Teaching notes

Students may be surprised that the bottles with the least and most mass topple at the same time. Encourage them to think about the how the mass is distributed in the bottles.

If students are unfamiliar with the idea of centre of gravity explain that it is the point on an object at which we can consider the gravity force to act. It is a sort of average position for the mass in the object. In the full and empty bottles the mass is distributed evenly and so the centre of gravity is at half way up the bottle. The half full bottle is different because it has an uneven distribution of mass and a lower centre of gravity.

When the bottles are upright, the gravitational force acts downwards through the base of the bottle (the area which is in contact with the board). As the bottle is tilted, it will remain in contact with the board until the line of action of the gravitational force falls outside the base -at which point it will topple over and so will no longer be stable. The full and empty bottles topple first because they have a higher centre of gravity and so reach their tipping points first; the half full bottle is more stable because it has a low centre of gravity.

Learning outcome

Students relate the stability of an object to the position of its centre of gravity relative to its base.

This experiment was safety-checked in March 2020.

Electrical Circuit
Electricity and Magnetism

Short series

Practical Activity for 11-14

This class activity allows students to investigate circuits with up to three bulbs without having to take their circuit apart. You can use it to test their understanding of current in series circuits.

Equipment

Each group of students will need:

  • Low voltage power supply (e.g. 1.5 V electrical cell)
  • Three identical bulbs
  • Two ammeters
  • Eight 4 mm leads

Preparation

Before the start of the lesson, set up one circuit as an exemplar so that students can refer to it if required.

During the activity students will need to bypass some of the bulbs by connecting leads around them. To avoid damaging the ammeters, ensure they don’t short circuit all the bulbs. There must be at least one bulb in the circuit to avoid the current becoming too high.

Procedure

Ask students to:

  1. Set up the circuit below. To start, they should connect leads around two of the bulbs so that only the first bulb is lit.
  2. Record the readings on both ammeters (A1 and A2).
  3. Predict what will happen when they remove lead Y.
  4. Disconnect lead Y and record observations.
  5. Repeat for lead Z.

Discussion prompts

  • Why must the ammeters readings always be the same?
  • Why do they go down when you disconnect the leads?

Teaching notes

Students may not understand how leads Y and Z allow them to change the number of bulbs in the circuit. Explain this in terms of the current taking the path of least resistance. The leads have a much lower resistance than the other components. Connecting a lead around a bulb means (almost) all the current will go through the lead, not the bulb.

There is only one loop in a series circuit and so an ammeter placed anywhere in the circuit will read the same. Disconnecting a lead adds another bulb in series, increasing the circuit’s overall resistance and so reducing the current throughout.

Learning outcome

Students predict and explain what will happen to the current when another light bulb is added in series.

This experiment was safety-checked in March 2020.

Magnetic Force
Electricity and Magnetism

Magnetic force pairs

Practical Activity for 14-16

This demonstration shows that the forces of attraction between two magnetically interacting objects are equal and opposite. You can use it as an example of Newton’s third law.

Equipment

  • Two identical small, strong neodymium magnets with holes in – the diameter of the hole should be large enough to thread string through (e.g. 2.5 mm)
  • Three 30 cm lengths of string
  • Two clamps and stands
  • Small bulldog clip
  • Two G-clamps(optional)

Preparation & safety

Rare-earth magnets are brittle and shatter easily. Don’t drill a hole into an existing magnet. Source neodymium magnets with pre-made holes or make a harness out of string or wire. When handling or moving magnets towards each other ensure that they don’t collide.

Before the activity, thread strings through each of the magnets and secure with a knot. Also tie one end of a string to the bulldog clip. Suspend the two magnets from a clamp stand so they hang around 10 cm below where the string is tied.

Setting the distance between the magnets and magnet and clip can take a bit of practice. Try it out beforehand. Mark positions on the bench and/or secure stands with G clamps to allow a quicker set-up next time.

Procedure

  1. Attach one magnet by its string to a clamp and secure the string tightly so that the magnet hangs around 10 cm below where the string is tied.
  2. Hang a second magnet from the second clamp. Arrange the stands so that the two magnets are close and attracting each other strongly with their strings almost horizontal.
  3. Repeat step 2 but replace one of the magnets with the bulldog clip.

Discussion prompts

  • What causes the magnetic force on the left magnet? What about the right magnet?
  • What causes the forces on the magnet and clip?
  • How do the size and direction of the forces compare?

Teaching notes

Students will be aware that magnets can attract each other and so will accept that two identical magnets pull equally on each other. The force on the left magnet is due to the right magnet; the one on the right is due to the left.

They may be surprised to see the same effect with the magnet and clip. These need to be closer to produce the same size forces but as previously the size of the forces are equal in size and opposite in direction. Like all interactions, magnetic interactions create Newton’s third law force pairs.

Learning outcome

Students identify Newton’s third law force pairs for objects that interact magnetically.

This experiment was safety-checked in March 2020.

Charge
Electricity and Magnetism

Attracting can

Practical Activity for 11-14

In this class activity, students see that after it’s rubbed against your clothes a balloon will attract a drinks can and make it roll. You can use it to introduce why charged objects exert forces on uncharged objects.

Equipment

Each student will need:

  • Empty aluminium soft drink can
  • Rubber balloon
  • Cloth or woollen clothing

Procedure

Ask students to:

  1. Inflate the balloon and tie its neck.
  2. Place the empty can on its side on a flat surface.
  3. Hold the balloon close to the can. They should see that nothing happens because the balloon is initially uncharged.
  4. Rub the balloon on their clothing or a piece of cloth so that it becomes charged.
  5. Bring the balloon close to the can. They should see the can start to move towards the balloon.
  6. Move the balloon gradually away from the can so that the can rolls along.

Discussion prompts

  • After it’s been rubbed, the balloon attracts the can. Have you seen this sort of thing before?
  • How can you tell that the forces on the aluminium can are unbalanced?
  • How do you think the balloon creates a force on the can?

Teaching notes

Charged objects attracting other objects may be familiar from, for example, a comb attracting hair. You could rub the balloon and show that it also attracts a student’s hair. To help them visualise charging processes, introduce electrons as negatively charged particles that move between the materials.

The balloon becomes charged when it’s rubbed because it’s made of a material that attracts electrons more strongly than the cloth. Electrons are transferred from the cloth to the balloon and so the balloon gains a negative charge overall. Explaining that the cloth is left with a positive charge will help students appreciate that charge is conserved, but there is no need to discuss atomic structure or the nature of the positive charge in the objects.

The charging process for the aluminium can is different. The two objects do not come into contact. Instead, electrons in the can are repelled by the balloon and so move to the part of the can furthest away. The back of the can becomes negatively charged and the front positive, but overall the can remains electrically neutral. The reason the aluminium can starts rolling is because the back of the can is further away and so the repulsive force on the back of the can is smaller than the attractive force on the front.

If students use the phrase ‘static electricity’, explain that it can be a misleading one. The charging process for the balloon involves the transfer of charge between cloth and balloon, and the process for the aluminium can involves charges moving within the can. The charging processes may be different, but in neither are the charges ‘static’.

Learning outcome

Students describe how an object made of an insulating material becomes charged when we rub it and also why it then attracts other objects.

This experiment was safety-checked in March 2020.

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