Law of Conservation of Energy
What does the Law of Conservation of Energy state in simplest terms?
Energy cannot be created or destroyed; it only changes forms.
Define kinetic energy in one sentence.
Kinetic energy is the energy of motion.
Name two different forms of energy other than kinetic and potential.
Examples: thermal, chemical, electrical, electromagnetic (light), nuclear, sound.
What type of energy transformation happens when you turn on a flashlight (from the battery to the light produced)?
Chemical energy (battery) → electrical energy → light (and some thermal).
A pendulum swings without friction. At which point does it have the greatest kinetic energy: at the highest point or the lowest point? Explain briefly in terms of the law.
Lowest point — greatest kinetic energy because potential energy is converted into kinetic energy; total energy conserved.
Define potential energy in one sentence.
Potential energy is energy stored due to an object's position or state.
What kind of energy does a stretched rubber band have?
Stretched rubber band stores elastic potential energy.
A toaster converts electrical energy into heat to toast bread. List the energy transformations involved, including any energy that might be considered "wasted."
Electrical → thermal (toasting). Wasted energy: some thermal energy lost to surrounding air, sound, and light.
A skateboarder starts at the top of a ramp with 1000 J of potential energy and no kinetic energy. Ignoring friction, how much mechanical energy does the skateboarder have at the bottom? (Answer in joules.)
1000 J (mechanical energy conserved = 1000 J).
A 2 kg toy car is moving at a speed of 3 m/s, a 3 kg toy car is moving at a speed of 3 m/s, and a final 5 kg toy car is moving at a speed 3 m/s. Which car has the most kinetic energy and why?
The 5 kg car has the most kinetic energy because it has the most mass.
Give an example (real-world) of chemical energy being converted into thermal energy.
Burning wood — chemical energy in wood → thermal energy (heat).
Describe the sequence of energy transformations for a hydroelectric power plant, starting with falling water.
Gravitational potential energy of stored water → kinetic energy of falling water → mechanical energy in turbines → electrical energy in generators → transmitted as electrical energy.
Explain why energy seems to "disappear" in a real system (like a ball rolling across rough ground) even though energy is conserved.
Energy is converted to other forms like thermal (heat) and sound due to friction.
Describe how an object's height and mass affect its gravitational potential energy and give a short example.
Gravitational potential energy increases with greater mass and greater height; doubling mass doubles PE, doubling height doubles PE. Example: a heavier book or placing the same book on a higher shelf increases PE.
Identify the form(s) of energy primarily involved when a solar panel produces electricity from sunlight.
Solar energy (electromagnetic) is converted into electrical energy; also some thermal energy may be produced.
A person rubs their hands together to warm them up. Explain which forms of energy are involved and how energy is being transformed.
Rubbing your hands together converts mechanical energy into thermal energy due to friction; some sound produced.
A closed system has a hair dryer that blows out warm air to dry hair. Describe how the Law of Conservation of Energy applies to this system and name the forms of energy involved before and after the hair dryer is on.
Electrical energy (input) is transformed into thermal and sound energy (outputs); total energy before equals total after (accounting for all forms).
A roller coaster car of mass 500 kg is at the top of a hill 20 m above ground. As it travels down the 20m hill to the ground, when does it have the most potential energy, and why?
It has the most potential energy at the top of the hill.
Explain how nuclear energy differs from chemical energy and give one example of where nuclear energy is used to produce electricity.
Nuclear energy comes from changes in an atom's nucleus (fission or fusion); chemical energy involves rearranging electrons in chemical bonds. Example: nuclear power plant uses nuclear fission to produce heat → steam → electricity.
Most cars are powered by gasoline. Describe at least four distinct energy forms/transformation steps from fuel to the car moving, including common energy losses.
Chemical energy in gasoline → thermal energy in engine combustion → mechanical energy in pistons → kinetic energy of car moving; losses include heat, sound, and friction.