Lesson overview
Energy, work and power: Where does the energy go on a roller coaster?
Predict which store the chain fills, then switch on the motor and watch the car climb the lift hill. Decide where the speed sensor goes, release the car and watch three energy bars change while their total stays the same. Ride again with friction and air resistance. Then work out the work done by the chain and the power of a slow and a fast lift, and check the kinetic energy in the dip.
Suggested sequence
- Lesson 1 · Energy stores and transfers. Energy stores and the ways energy is transferred between them; the conservation of energy, with flow diagrams; Supplement: Sankey diagrams for more complex examples. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Work and power. Work done as energy transferred, W = Fd; power as work done or energy transferred per unit time; Supplement: kinetic energy ½mv² and gravitational potential energy mgΔh. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 4 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 4 questions, 15 min, lesson closed.
Learning goals
Part 1: Energy stores and transfers
- State that energy may be stored as kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal) (1.7.1.1)
- Describe how energy is transferred between stores during events and processes, including examples of transfer by forces (mechanical work done), electrical currents (electrical work done), heating, and by electromagnetic, sound and other waves (1.7.1.2)
- Know the principle of the conservation of energy and apply this principle to simple examples including the interpretation of simple flow diagrams (1.7.1.3)
- Supplement: Know the principle of the conservation of energy and apply this principle to complex examples involving multiple stages, including the interpretation of Sankey diagrams (1.7.1.6)
Part 2: Work and power
- Understand that mechanical or electrical work done is equal to the energy transferred; recall and use the equation for mechanical working W = Fd = ∆E (1.7.2.1, 1.7.2.2)
- Define power as work done per unit time and also as energy transferred per unit time; recall and use the equations P = W / t and P = ∆E / t (1.7.4.1)
- Supplement: Recall and use the equation for kinetic energy Ek = ½mv² and the equation for the change in gravitational potential energy ∆Ep = mg∆h (1.7.1.4, 1.7.1.5)
Misconceptions to listen for
- “Kinetic, because the bits of paper move.” — Kinetic energy belongs to moving objects. The ruler is held still; the paper only starts to move because the ruler pulls on it.
- “Chemical, because plastic is a chemical.” — The chemical store is energy released by chemical reactions, as in fuels, food and batteries. Rubbing does not change what the plastic is made of.
- “Nuclear, because the energy is inside the atoms.” — The nuclear store is energy in the nuclei of atoms, released in nuclear reactions such as those in a power station. Rubbing a ruler does not change its nuclei.
- “A hot iron has heat energy stored in it.” — Heating is a way energy is transferred. The energy kept in a hot object is in its internal (thermal) store.
- “Americium is a chemical element, so its energy is chemical.” — Every substance is made of elements. Chemical energy is released when substances react, as when candle wax burns. Americium is radioactive: its energy is in the nuclei of its atoms, in its nuclear store.
- “As she rolls down, her kinetic store empties.” — She gets faster as she rolls down, so her kinetic store fills. It is her gravitational potential store that empties, because she gets lower.
- “Heat is a store of energy.” — Heating is a way energy is transferred. The energy kept in a warm object is in its internal (thermal) store.
- “The lighthouse lamp is hot, so its light transfers energy by heating.” — Heating moves energy from a hotter object to the cooler things around it, as the radiator warms the air. The light crosses the sea as an electromagnetic wave.
- “The current in a toaster transfers energy by heating.” — The current does electrical work on the toaster’s wires. The hot wires then heat the bread, but the current itself transfers energy by electrical work.
- “Row A.” — There is no electrical store. A battery keeps its energy in its chemical store; electrical work is how the current transfers it to the lamp.
Scope
Energy stores: kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal) (1.7.1.1); transfers between stores by forces (mechanical work done), electrical currents (electrical work done), heating, and electromagnetic, sound and other waves (1.7.1.2); the principle of the conservation of energy, applied to simple examples including the interpretation of simple flow diagrams (1.7.1.3); Supplement: kinetic energy, Ek = ½mv² (1.7.1.4), change in gravitational potential energy, ΔEp = mgΔh (1.7.1.5), and the conservation of energy applied to complex examples, with Sankey diagrams (1.7.1.6); mechanical or electrical work done as energy transferred (1.7.2.1), W = Fd = ΔE (1.7.2.2); power as work done per unit time and energy transferred per unit time, P = W/t = ΔE/t (1.7.4.1). Energy resources and efficiency (1.7.3) are left to the next module, and electrical power (4.2.5) to the electricity modules.