Review the energy strand from Lessons 15-19, then test yourself with 10 multiple-choice questions and 3 short-answer questions.
Quick Review
Focus: Energy is the capacity to cause change, measured in joules (J). It comes in many forms (kinetic, gravitational and elastic potential, chemical, thermal, light, electrical, sound), and the law of conservation of energy says it cannot be created or destroyed, only transformed.
Key terms: Energy, Joule, Conservation of energy
Focus: Kinetic energy is the energy of motion. It depends on both mass and speed, but speed has a squared effect, so doubling the speed quadruples the kinetic energy. This is why crashes at higher speeds are far more dangerous.
Key terms: Kinetic energy, Mass, Speed
Focus: Gravitational potential energy is stored by height (depends on mass and height) and elastic potential energy is stored in a stretched or compressed material. Potential and kinetic energy constantly convert into each other in pendulums and roller coasters.
Key terms: Gravitational potential energy, Elastic potential energy, Elastic limit
Focus: Every device transforms energy from one form to another along an energy chain. Efficiency is the percentage of input energy that becomes useful output: efficiency (%) = (useful output ÷ total input) × 100. No device is 100% efficient, and the "lost" energy almost always becomes heat or sound.
Key terms: Energy transformation, Efficiency, Waste energy
Focus: Temperature is the average kinetic energy of particles, while heat (thermal energy) is the total energy of all particles, so they are not the same thing. Heat moves by conduction (solids), convection (fluids) and radiation (electromagnetic waves, the only method that works through a vacuum).
Key terms: Heat, Temperature, Conduction, Convection, Radiation
Multiple Choice (10 questions)
1. In science, energy is best defined as:
2. What is the SI unit of energy?
3. A book resting on a high shelf, not moving, mainly stores:
4. If a car keeps the same mass but doubles its speed, its kinetic energy:
5. A wound-up clock spring stores which type of energy?
6. The law of conservation of energy states that energy:
7. In a hydroelectric power station, flowing water spins a turbine. This step converts:
8. A device takes in 200 J of energy and produces 50 J of useful output. What is its efficiency?
9. In a coal-fired power station, the chemical energy in coal is FIRST converted to:
10. The Sun warms the Earth across the vacuum of space. Which method of heat transfer makes this possible?
Short Answer (3 questions)
Model answer: (a) A charged battery stores chemical energy (1 mark). (b) A ball at the top of a ramp stores gravitational potential energy, stored because of its height (1 mark). (c) A stretched rubber band stores elastic potential energy, stored in its stretched shape (1 mark).
Model answer: Kinetic energy depends on the square of the speed, so doubling the speed (50 to 100 km/h) multiplies the kinetic energy by 2 squared, which is 4 times, not 2 (1 mark). This matters for road safety because the car carries four times as much energy that must be absorbed in a crash, so even small increases in speed make collisions much more dangerous and greatly increase stopping distance (1 mark).
Model answer: The chemical energy stored in the battery is converted to electrical energy, which flows to the bulb (1 mark). The bulb converts this to light energy (the useful output) and thermal energy or heat (the waste energy), so the chain is chemical to electrical to light plus heat (1 mark). By the law of conservation of energy, the waste energy is not destroyed; it spreads into the surroundings as heat, where it is hard to reuse, so the total energy stays the same (1 mark).
Put what you have reviewed to the test! Jump through the checkpoint questions in game form.
Play GameTick the box when you have finished the questions and played the game.