Pick a goal, then build a chain: choose an energy source and up to three devices. Each device needs the right form of energy in. The Sankey diagram shows 100 J going in and how it splits into useful energy (bright band) and wasted energy (red, mostly thermal). Solve 4 of the 6 goals.
Numbers are typical values for real devices (for example a solar panel turns about 20 % of the light into electrical energy, an LED bulb about 30 % of its electrical energy into light).
12 everyday things. Choose the main form of energy each one has. Get 10 or more right in one round.
All three bulbs give about the same brightness (about 800 lumens). Switch one on for a number of hours. Energy used: E = P × t (watts × hours = watt-hours, Wh). Then answer 2 calculation questions.
| # | Bulb | Power (W) | Time (h) | Energy in (Wh) | Light (Wh) | Thermal (Wh) | Efficiency |
|---|
A Sankey diagram shows energy as a flow: the width of each arrow is the amount of energy. Energy in = useful out + wasted. Efficiency = useful ÷ total in × 100 %. Find the missing number. Get 3 right on the first try.
Each energy chain has one wrong form of energy. Click the wrong step. You get one try per chain; 6 of 8 right completes the mission.
Click a card, then the group it belongs in (or its “Place card here” button). Kinetic = energy of motion. Stored (potential) = gravitational, elastic, chemical or nuclear energy waiting to be used. All 12 right with at most 2 mistakes per check; more than 2 sends every card back.
10 questions from a bank of 20. Score 7 or more to complete the mission. Each new round picks new questions.
Anything that moves, lights up, makes a sound or gets warm needs energy. A flashlight is a good example: the battery stores chemical energy, the circuit carries electrical energy, and the bulb gives out light, and gets a little warm (thermal energy). We can write that as an energy chain: chemical → electrical → light + thermal.
Some forms are stored (potential) energy, waiting to be used: chemical (food, fuel, batteries), gravitational (anything raised up), elastic (springs, rubber bands) and nuclear (inside atoms). Others are energy on the move: kinetic (motion), thermal (moving particles), light, sound and electrical energy. Devices change one form into another: a solar panel changes light into electrical energy, a motor changes electrical energy into motion, a speaker changes electrical energy into sound.
If 100 J of electrical energy goes into an LED bulb, about 30 J comes out as light. The other 70 J is not destroyed: it warms the bulb and the room. Energy that does not do the job we want is called wasted energy, and it almost always ends up as thermal energy spread through the surroundings. Efficiency = useful energy out ÷ total energy in × 100 %. An incandescent bulb is only about 5 % efficient, which is why LEDs save so much energy for the same light.
In a chain, the efficiencies multiply: a power station that burns fuel (85 % into steam), spins a turbine (40 %) and a generator (90 %) delivers about 0.85 × 0.40 × 0.90 ≈ 31 % of the fuel’s energy as electricity (real fuel-burning power stations are roughly 30–45 % efficient). A Sankey diagram draws this as arrows whose widths are the amounts of energy, so you can see at a glance where most of it goes. Engineers improve a system by attacking the biggest waste first (for example, using the hot water from a power station to heat buildings).
In the Energy Chain Lab, light a room with sunlight twice: once with an LED and once with an incandescent bulb, and compare the Sankey diagrams. Then make electricity from fuel and find which step wastes the most energy. In the Light-Bulb Lab, run the 60 W and the 9 W bulb for the same time and compare the thermal-energy bars.
| Form | Stored or on the move? | What it is | Examples |
|---|---|---|---|
| Chemical | Stored | Energy in the bonds between atoms, released in reactions | Food, fuel, wood, batteries |
| Gravitational potential | Stored | Energy of an object because of its height | Water behind a dam, a book on a shelf |
| Elastic potential | Stored | Energy in something stretched or squashed | Springs, rubber bands, a bent bow |
| Nuclear | Stored | Energy in the nucleus of atoms | The Sun (fusion), nuclear power plants (fission) |
| Kinetic | On the move | Energy of a moving object | Wind, a rolling ball, a spinning motor |
| Thermal | On the move | Energy of the moving particles in a substance; hotter = more | Hot soup, a warm engine, a heater |
| Light (radiant) | On the move | Energy carried by light and other electromagnetic waves | Sunlight, a lamp, a screen |
| Sound | On the move | Energy of vibrations traveling through matter | A beep, thunder, a voice |
| Electrical | On the move | Energy carried by moving electric charges | Current in a wire, lightning |
Some courses use “energy stores” (kinetic, gravitational, elastic, thermal, chemical, nuclear, …) and “energy transfers” (by heating, by light, by sound, by an electric current, by forces). The ideas are the same: energy moves between stores and is never lost. Related pages: kinetic and potential energy (roller coaster lab), heat transfer, photosynthesis, electric circuits.
Kinetic energy: KE = ½ m v². Gravitational potential energy near Earth: GPE = m g h with g = 9.8 N/kg. A 2 kg ball raised 5 m has GPE = 2 × 9.8 × 5 = 98 J. Dropped (no air resistance), all 98 J becomes kinetic energy just before it lands: ½ × 2 × v² = 98, so v = √(2gh) ≈ 9.9 m/s.
Power is the rate of energy transfer: P = E ÷ t, in watts (1 W = 1 J/s). So E = P × t. A 60 W bulb on for 1 hour uses 60 × 3600 = 216,000 J = 60 Wh = 0.06 kWh. Electricity is sold by the kilowatt-hour: swapping it for a 9 W LED saves 51 Wh every hour.
Efficiency η = Euseful ÷ Ein. For devices in a row the efficiencies multiply: ηtotal = η1 × η2 × η3. Sunlight → solar panel (0.20) → LED (0.30) gives 0.06, so only 6 % of the light falling on the panel comes back out as light.
For a system, the change in internal (thermal) energy equals the energy added by heating minus the work the system does: ΔU = Q − W. Energy accounting always balances; what changes is how useful the energy is. Spread-out thermal energy at room temperature is very hard to turn back into work, which is why efficiencies are limited (the second law).
Design a device that converts one form of energy into another, for example a solar oven, a hand-crank flashlight or a rubber-band car. Measure the energy in and the useful energy out, draw the Sankey diagram, find the biggest waste and change one thing to reduce it.
Standards: NGSS 4-PS3-2, 4-PS3-4 (upper elementary); MS-PS3-5, supports MS-PS3-3 (middle school); HS-PS3-1, HS-PS3-3 (Going further). Objective: students name the forms of energy, trace energy chains, explain conservation of energy and calculate efficiency and E = P × t.
Misconceptions to target: energy is “used up”; a battery stores electricity; potential energy means only height; LEDs make no heat. Missions are saved on the student’s device; the certificate prints as proof of completion.
Many science textbooks list nine forms. Stored (potential) forms: chemical energy (food, fuel, batteries), gravitational potential energy (anything raised up), elastic potential energy (springs, rubber bands) and nuclear energy (inside atoms). Forms on the move: kinetic energy (motion), thermal energy (moving particles), light (radiant) energy, sound energy and electrical energy.
Key takeaway: four stored forms and five forms on the move.An energy transformation is a change of energy from one form into another. A solar panel transforms light into electrical energy; an electric motor transforms electrical energy into kinetic energy; your muscles transform chemical energy from food into motion. A chain of transformations, such as chemical → electrical → light in a flashlight, is called an energy chain.
Key takeaway: one form of energy changing into another.Energy cannot be created or destroyed. It can only change form or move from one place to another, so the total amount of energy stays the same. When a ball stops bouncing, its energy has not vanished: it has become thermal energy in the ball and the floor, and sound.
Key takeaway: the total amount of energy never changes.Kinetic energy is the energy of a moving object; the faster and heavier it is, the more kinetic energy it has. Potential energy is stored energy that depends on position or shape or chemical makeup: a raised rock (gravitational), a stretched spring (elastic) or a battery (chemical). Stored energy can be turned into kinetic energy, as when a raised rock falls.
Key takeaway: kinetic = moving; potential = stored.Electrical energy is transformed into light and thermal energy. An incandescent bulb turns only about 5 % of the electrical energy into light; the rest heats the bulb. An LED bulb turns about 30 % into light, so a 9 W LED gives about the same light as a 60 W incandescent bulb and wastes far less energy as heat.
Key takeaway: electrical → light + thermal; LEDs waste much less.Efficiency = useful energy out ÷ total energy in × 100 %. If a motor takes in 200 J of electrical energy and gives out 170 J of kinetic energy, its efficiency is 170 ÷ 200 × 100 = 85 %. The other 30 J is wasted, mostly as thermal energy. Efficiency can never be more than 100 %.
Key takeaway: useful out divided by total in.In every real device some energy is turned into forms we do not want, mostly thermal energy from friction and from electric current flowing through wires, plus some sound. That energy spreads out into the surroundings and is very hard to collect and use again. So the useful output is always less than the energy put in.
Key takeaway: some energy always spreads out as heat.A Sankey diagram shows energy flowing through a device or system as arrows. The width of each arrow is proportional to the amount of energy. The input arrow splits into a useful-energy arrow and wasted-energy arrows, so the widths always add up. They make it easy to see where most of the energy goes.
Key takeaway: arrow widths show the amounts of energy.In a fuel-burning power station, chemical energy in the fuel becomes thermal energy in steam, the steam spins a turbine (kinetic energy) and the turbine turns a generator (electrical energy). In a hydroelectric dam, gravitational potential energy of the water becomes kinetic energy, spins a water turbine and generator, and becomes electrical energy. A wind turbine turns the kinetic energy of the wind into electrical energy.
Key takeaway: chemical → thermal → kinetic → electrical in a fuel power station.Energy is the amount, measured in joules (J) or kilowatt-hours (kWh). Power is how fast energy is transferred, measured in watts (W): 1 W = 1 J per second. A 60 W bulb uses 60 J every second; leave it on for 1 hour and it uses 60 Wh = 216,000 J.
Key takeaway: power is the rate; energy is the amount.