Energy
9th Grade Science · 10 lessons
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Lessons in this unit
- 1Work Done Is Force Times DistanceWork is done when a force moves its point of application along its own direction: W = Fs, in joules. Hold a heavy bag still and you do no work in the physics sense, however tired your arm gets, because nothing moves.Experiment
- 2Kinetic Energy Grows With the Square of SpeedKinetic energy is ½mv². Because speed is squared, doubling a car's speed quadruples its kinetic energy — and roughly quadruples its braking distance. That single relationship is the physics behind most speed limits.Experiment
- 3Gravitational Potential EnergyLift a mass and you store energy in the gravitational field: Ep = mgh. The store depends only on the vertical height gained, not on the path taken, so carrying a rucksack up a zigzag trail stores the same energy as hauling it straight up.Experiment
- 4Conservation of EnergyEnergy cannot be created or destroyed, only shifted between stores and transferred by heating, working, radiation or electric current. A pendulum trades gravitational store for kinetic store and back, losing a little to thermal store with every swing.Experiment
- 5Power: How Fast Energy Is TransferredPower is energy transferred per second, in watts. A 2,000 W kettle transfers twice as much energy per second as a 1,000 W one, so it boils the same water in half the time and costs the same to do it.Experiment
- 6Efficiency and Useful OutputEfficiency is useful output energy divided by total input, usually given as a percentage. No real device reaches 100%: some energy always ends up dissipated as heat. An LED lamp reaching about 40% beats an old filament bulb at roughly 5%.Experiment
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