Energy Transmission — Heat
Three kitchen demonstrations and one research question. Everything here can be done with a kettle, two jars and some food colouring — and the one investigation CAPS actually sets is about a bird hitting the sea at a hundred kilometres an hour.
Investigations column, block 12, in full: "How do various birds adapt to refraction and pressure when diving from air into water?"
That is Investigation 4. Investigations 1–3 come from the booklet's own core concepts, which ask you to "draw a simple diagram to indicate the three forms of heat energy", to "explain how heat differs from temperature", and to "discuss convection currents in water". All three are kitchen-tier.
What you need
- 🟢 kitchen A kettle, two clear glass jars of the same size, and a metal spoon
- 🟢 kitchen Food colouring — dark colours work best
- 🟢 kitchen A kitchen thermometer, ice, and a measuring jug
- 🟢 kitchen A stopwatch (your phone), pencil and ruler
- 🟡 optional A cheap digital thermometer with a probe, if your kitchen one will not sit in a jar
Every measured investigation on this sheet carries a supplied data panel, so you can complete the tables, the calculations and every analysis question without running anything. Investigation 4 is a research task and needs no apparatus at all — its evidence is supplied too.
Aim
To observe conduction, convection and radiation, and to draw a labelled diagram showing all three forms of heat energy.
Method
- Conduction. Stand a metal spoon in a mug of just-boiled water, handle sticking out. Touch the handle after 10 s, 30 s and 60 s. Record how it feels each time.
- Convection. Fill a jar with cold water and let it settle completely still. Add one drop of food colouring at the surface, then place the jar on a warm surface, or rest it in a bowl of hot water so the base warms. Watch the dye for two minutes and sketch what it does.
- Radiation. Hold your palm about 10 cm to the side of the mug — not above it, so you are not feeling rising warm air. Record what you feel. Then slide a sheet of card between your palm and the mug and record what changes.
Supplied results — if you cannot run it
Conduction. At 10 s the handle is barely warm. At 30 s it is noticeably warm. At 60 s it is uncomfortable to hold. The heat has travelled up the solid metal without any of the metal moving.
Convection. The dye first sits as a flat layer at the surface. Once the base warms, a thin plume of colour lifts from the bottom of the jar, spreads across the top, drifts down the sides and returns to the base — a visible loop. Within two minutes the whole jar is faintly and evenly coloured.
Radiation. The palm feels a steady warmth from the side, with nothing touching it and no air movement. Sliding the card in front cuts the warmth off immediately, not gradually.
Results — draw the three forms of heat energy
Analysis
- Draw one labelled diagram showing all three forms of heat energy. Marks: all three modes shown and named (3), direction of heat flow shown with arrows (3), a correct example of each labelled (3), pencil and ruled label lines as per Topic 5 (1). 10
- Explain, at the level of molecules, how heat travelled from the water to the top of the spoon handle. 4
- In the convection jar, explain why the warmed water rose and the cooler water sank. Use the word density. 4
- Sliding a card in front of your palm cut the warmth off instantly. What does that tell you about how radiated heat travels, and how is that different from the other two modes? 4
- Which of the three modes can operate through a vacuum? Explain why the other two cannot. 3
- Water is a less effective conductor than metal. Give one consequence of that for the ocean. 2
Aim
To show that two samples at the same temperature can contain different amounts of heat, and to measure the difference.
Method
- Measure 100 mL of just-boiled water into jar A, and 300 mL of just-boiled water into jar B.
- Measure and record the starting temperature of each. They should be almost identical.
- Add exactly 50 g of ice to each jar at the same moment.
- Stir gently. Record the temperature of each jar every 30 s for 3 minutes.
- Record which jar melted its ice first.
Supplied results — 100 mL vs 300 mL, both starting at 96 °C
| Time (s) | 0 | 30 | 60 | 90 | 120 | 150 | 180 |
|---|---|---|---|---|---|---|---|
| Jar A — 100 mL | 96 | 61 | 44 | 36 | 33 | 32 | 31 |
| Jar B — 300 mL | 96 | 84 | 77 | 73 | 71 | 70 | 70 |
Jar B melted all its ice in about 70 s. Jar A still had unmelted ice at 150 s.
Results
| Time (s) | 0 | 30 | 60 | 90 | 120 | 150 | 180 |
|---|---|---|---|---|---|---|---|
| Jar A — 100 mL | |||||||
| Jar B — 300 mL |
Analysis
- Both jars started at the same temperature. Did they contain the same amount of heat? Justify your answer using the results. 4
- Define heat and temperature so that the difference between them is clear. 4
- Jar B melted its ice much faster despite starting at the same temperature. Explain why. 4
- Calculate the temperature drop in each jar over the full 180 s, and state which fell further. 3
- Identify the independent variable, the dependent variable and two variables that had to be kept fixed. 5
- Using water's heat capacity of 1 calorie per gram per °C, calculate roughly how many calories jar A lost over the 180 s. (Treat 100 mL as 100 g.) 4
Aim
To compare what happens when a body of water is heated from below with what happens when it is heated from above — the comparison CAPS uses to explain why the ocean is an inefficient heat mover and the atmosphere an efficient one.
Method
- Fill two identical jars with cold water and let both settle until completely still.
- Add one drop of food colouring to the bottom of each jar, using a straw so the dye reaches the base without mixing.
- Jar A — heated from below. Stand it in a shallow bowl of hot water.
- Jar B — heated from above. Leave it on the counter and float a small dish of hot water on the surface, or shine a desk lamp closely on the top of the water. Do not let anything touch the sides.
- Observe both for 5 minutes. Sketch the dye pattern in each at 1 min and at 5 min.
- At the end, measure the temperature at the top and at the bottom of each jar.
Supplied results
Jar A (below). Within a minute the dye lifts off the base in plumes, reaches the surface, spreads outward and sinks down the sides. By 5 minutes the water is uniformly tinted. Final temperatures: top 31 °C, bottom 33 °C — nearly the same.
Jar B (above). The dye stays where it was put. At 5 minutes there is a faint tint in the lowest centimetre and clear water above it. Final temperatures: top 38 °C, bottom 19 °C — a difference of 19 °C in one small jar.
Results
| Dye at 1 min | Dye at 5 min | Final top °C | Final bottom °C | |
|---|---|---|---|---|
| Jar A — heated below | ||||
| Jar B — heated above |
Analysis
- Describe the difference between the two jars in one sentence. 2
- Explain, using density, why heating from below produces a circulating current but heating from above does not. 5
- Which jar represents the ocean, and which represents the atmosphere? Justify both. 4
- CAPS says heat transmission from the ocean surface is inefficient while transfer to the atmosphere is efficient. Use your results to explain why. 5
- In jar B, some heat did reach the bottom. By which mode, and why was it so slow? 3
- CAPS adds that in the ocean, "the deeper heated water will in turn move upward and float above bands of water colder than it." Explain what that produces, and name the layered boundary you met in Topic 4. 4
Aim
To investigate how various birds adapt to refraction and pressure when diving from air into water.
Method — two parts
- See refraction for yourself (🟢 kitchen, 2 minutes). Put a coin at the bottom of an opaque mug. Move back until the coin just disappears behind the rim. Without moving your head, have someone slowly pour water into the mug. Record what happens to the coin.
- Then research the birds. Read the three supplied bird cards and complete the table. If you have internet access, add a fourth bird of your own.
Supplied data — three diving birds, and what the water does to light
The physics, briefly. Light changes speed when it crosses between air and water, so it bends at the boundary — that is refraction. A fish viewed from above is therefore not where it appears to be: it looks shallower and displaced. And once a bird's eye is underwater, the front surface of its eye no longer bends light much at all, because eye fluid and seawater are optically similar — so an eye built for air becomes badly long-sighted underwater.
Pressure is the second problem, and it comes in two forms: the impact of hitting the surface at speed, and the squeeze of water pressure with depth.
Cape Gannet
Solves refraction by not fighting it: it dives steeply and fast, so the light path bends least and the aiming error is smallest, and it commits before the fish can react. Against impact it has a reinforced skull, no external nostrils (they are internal, so water is not forced in), and air sacs under the skin of the face, neck and chest that cushion the blow. Bird Island in Algoa Bay holds one of the world's largest breeding colonies.
Cape Cormorant
Does not plunge — it swims. That means its eyes must work underwater, so it has an exceptionally deformable lens and powerful ciliary muscles that squeeze the lens into a much rounder shape, restoring the focusing power the cornea loses in water. Its feathers are also less waterproof than most seabirds', which reduces buoyancy and makes diving easier — and is why you see cormorants standing with wings spread, drying out.
African Penguin
Lives the problem permanently. Against pressure it has dense, solid bones rather than the air-filled bones of flying birds, which cuts buoyancy and resists the squeeze; it can collapse its air sacs and slow its heart rate to stretch one breath. Its eye is adapted for underwater vision, at some cost to sharpness in air — the opposite trade-off to the gannet.
Results
| Bird | Diving style | Adaptation to refraction / vision | Adaptation to pressure |
|---|---|---|---|
| Cape Gannet | |||
| Cape Cormorant | |||
| African Penguin |
Analysis
- Describe what happened to the coin when water was poured into the mug, and explain why. 4
- Complete Table 4.1. 9
- Explain why a fish seen from above the surface is not where it appears to be, and what that means for a bird aiming at it. 4
- A gannet plunges almost vertically. Explain two separate advantages of a steep, fast entry — one about refraction, one about the prey. 4
- Cormorants are less waterproof than most seabirds. Explain how a disadvantage on the surface becomes an advantage underwater. 3
- The gannet's eye works best in air; the penguin's works best in water. Explain why neither bird can have both, using the word trade-off. 4
- Flying birds have air-filled bones. Penguins have solid ones. Explain how giving up flight made deep diving possible. 4
- Extension. This investigation is about refraction, which is a property of light, not heat. Explain why CAPS still puts it in the energy-transmission block. 3
Memo — worked answers and mark allocation (does not print)
Total: 109 marks — Investigation 1: 27 · Investigation 2: 24 · Investigation 3: 23 · Investigation 4: 35.
Investigation 1 — three modes
- Q1 (10): Look for the sun radiating to a surface, a solid (spoon, anchor chain, seabed) conducting, and a fluid loop rising and sinking. A common loss is drawing convection as a single upward arrow with no return path — convection is a circulation.
- Q2 (4): Heat makes the water molecules move faster (1). They collide with the metal atoms at the spoon's surface, passing energy on (1). Those atoms vibrate harder and collide with their neighbours further up the handle (1), and the energy travels along the metal while the metal itself stays put (1).
- Q3 (4): Warmed water expands slightly, so the same mass occupies more volume and it becomes less dense (2), so it rises. At the surface it loses heat, becomes more dense than the water below (1), and sinks — producing a loop (1).
- Q4 (4): The warmth stopped instantly, so it was travelling in straight lines that the card could block (2) — as waves, not by heating the air in between (1). Conduction and convection would have continued for a while because the warmed air and surfaces would still be there (1).
- Q5 (3): Radiation (1). Conduction needs molecules in direct contact and convection needs a fluid that can move; a vacuum has neither (2).
- Q6 (2): Any one, well explained: heat cannot spread downward through the ocean by conduction at any useful rate, so the deep ocean stays cold; or the ocean must rely on convection and currents to move heat at all. (2)
Investigation 2 — heat vs temperature
- Q7 (4): No (1). Jar B held three times as much water at the same temperature, so it held about three times the heat (2) — shown by it melting the ice faster and ending 39 °C higher (1).
- Q8 (4): Heat = the total kinetic energy of all the particles in a substance, so it depends on how many there are (2). Temperature = the average kinetic energy per particle, so it does not (2).
- Q9 (4): Melting ice needs a fixed quantity of energy (1). Jar B had far more total heat available (2), so it could supply that energy without its own temperature dropping much (1).
- Q10 (3): Jar A: 96 − 31 = 65 °C (1). Jar B: 96 − 70 = 26 °C (1). Jar A fell further (1).
- Q11 (5): Independent: volume of water (1). Dependent: temperature (1). Fixed, any two (3): starting temperature, mass of ice, jar shape and material, stirring, room temperature, timing intervals.
- Q12 (4): 100 g × 65 °C × 1 cal/g/°C (2) = 6 500 calories (1), ≈ 27 kJ (1). Accept the answer without the joule conversion.
Investigation 3 — above vs below
- Q13 (2): Heated from below the whole jar mixed and ended at almost one temperature; heated from above it stayed layered, with a large top-to-bottom difference.
- Q14 (5): Heating from below warms the bottom layer, making it less dense than the water above it (2) — an unstable arrangement, so it rises and cold water sinks to replace it, and the loop keeps running until the jar is mixed (2). Heating from above puts the warm, less dense water on top, which is already the stable arrangement, so nothing has to move (1).
- Q15 (4): Jar B (above) = the ocean, heated at its surface by solar radiation (2). Jar A (below) = the atmosphere, heated from beneath by the land and sea (2).
- Q16 (5): The ocean's heat stays near the surface because there is no density instability to drive mixing — 19 °C difference across one small jar (3). The atmosphere is heated from below, so warm air must rise, and vertical movement of air carries heat efficiently (2).
- Q17 (3): By conduction (1) — water is a poor conductor (1), and conduction is slow because energy passes molecule to molecule with no bulk movement to help it (1).
- Q18 (4): Layers, or stratification — bands of water at different temperatures stacked with the warmest on top (2). The boundary is the thermocline (2).
Investigation 4 — the diving bird
- Q19 (4): The hidden coin reappears (1). Light from the coin bends as it leaves the water and enters the air (2), so it now reaches the eye along a path the straight rim previously blocked (1).
- Q20 (9): Three rows, three columns of content each. Gannet: plunge diver / steep fast entry minimises the aiming error / reinforced skull, internal nostrils, facial and neck air sacs. Cormorant: pursuit diver / deformable lens and strong ciliary muscles restore focus underwater / less waterproof plumage reduces buoyancy. Penguin: deep pursuit diver / eye adapted for underwater focus / solid dense bones, collapsible air sacs, reduced heart rate.
- Q21 (4): Light bends where it leaves the water (1), so the fish appears shallower and displaced from its true position (2). A bird aiming at the image would miss, so it must either correct for the offset or remove the problem (1).
- Q22 (4): Refraction: a steep, near-vertical path crosses the surface close to head-on, where the bending is least, so the aiming error is smallest (2). Prey: the speed of entry gives the fish almost no time to react, and carries the bird several metres down before it must swim (2).
- Q23 (3): Wet feathers hold less trapped air, so the bird is less buoyant (2) and does not have to fight to stay under — at the cost of getting cold and waterlogged on the surface, hence the wing-drying (1).
- Q24 (4): The cornea only bends light when air is on the other side of it (2). An eye shaped to focus correctly in air is therefore wrong underwater, and one that focuses underwater is wrong in air — so any eye is a trade-off, and each bird's is tuned to where it does most of its hunting (2).
- Q25 (4): Air-filled bones are light, which flight requires (1), but they add buoyancy and are more vulnerable to being squeezed (1). Once a bird no longer needs to fly, solid bones become an advantage — less buoyancy to overcome and better resistance to pressure (2).
- Q26 (3): Because the block is about how energy moves through water, not only heat (1). CAPS's own first key concept is that energy is transmitted in water in three ways — heat, light and sound (1) — so refraction is the light case, and it points forward to the light block (1).
Marking note. Q1 is the only drawing mark on the sheet and it is worth 10. Mark it against the four stated criteria, not on artistic quality — a rough but correctly labelled diagram beats a beautiful one that shows convection as a single arrow.