Energy Stores and Transfer Pathways Study Guide
Fundamental Energy Concepts and Energy Stores
Definition of a System: In physics, a system is defined as an object or a group of objects.
The Law of Conservation of Energy: This fundamental law states that energy cannot be created or destroyed; it can only be transferred from one store to another.
The Eight Energy Stores (GEEKMNCH):
Gravitational Potential Energy: Energy stored in systems that have been raised above the ground.
Elastic Potential Energy: Energy stored in objects that are stretched or compressed.
Electrostatic Energy: Energy stored in charged systems.
Kinetic Energy: Energy stored in all moving systems.
Magnetic Energy: Energy stored in magnets and electromagnets.
Nuclear Energy: Energy stored within the nucleus of atoms.
Chemical Energy: Energy stored within the bonds between particles (e.g., in food, fuel, or batteries).
Heat (Thermal) Energy: Energy stored in all hot systems.
The Four Pathways of Energy Transfer
Energy does not remain static in one store; it is constantly changing and being transferred between stores via four specific pathways:
Mechanically: This occurs whenever a force causes energy to be transferred.
Example 1: Friction acting on a moving object.
Example 2: Gravitational force pulling objects down.
Electrically: This occurs whenever an electric charge moves or a current flows.
Example 1: Battery-powered devices.
Example 2: Electrical appliances using mains electricity in the home.
Heating: This occurs whenever an object changes temperature or changes state.
Example 1: Hot objects cooling down to room temperature.
Example 2: Hot objects causing other objects to increase in temperature.
Radiation: This occurs whenever energy is transferred by a wave.
Example 1: A light bulb emitting light waves.
Example 2: A drum emitting sound waves.
Example 3: Electromagnetic waves (such as light or infrared) traveling through the vacuum of space.
Useful vs. Wasted Energy and Efficiency
Useful Energy: These are energy transfers that we specifically want to happen for the device to perform its intended function.
Wasted Energy: These are energy transfers that we do not want to happen. Wasted energy is typically dissipated to the surroundings, meaning it spreads out and becomes less useful.
Common Forms of Wasted Energy: Wasted energy is most often transferred as Heat (Thermal) energy.
Mathematical Relationship (Conservation): The total energy transferred into a system is always equal to the sum of the useful energy and the wasted energy. This is because energy cannot be created or destroyed.
Formula Demonstration 1: If a total of of energy is transferred and is useful, the wasted energy is .
Formula Demonstration 2: If a system transfers usefully and is wasted, the total energy transferred is .
Reducing Unwanted Energy Transfers
To improve the efficiency of a system, methods must be employed to reduce wasted energy:
Lubrication: Applying a lubricant (like oil) reduces the amount of friction between moving parts. This specifically reduces the amount of unwanted energy dissipated mechanically as heat.
Thermal Insulation: This reduces the amount of unwanted energy transferred via heating between objects of different temperatures (e.g., insulation in the walls of a house or around a kettle).
Detailed Energy Transfer Analysis by System
Dropping a Ball from a Height:
The Gravitational Potential energy store decreases.
The Kinetic energy store increases.
Energy is transferred Mechanically.
Driving a Petrol-Powered Car:
The Chemical energy store (in the fuel) decreases.
The Kinetic energy store (of the car) increases.
Energy is transferred Mechanically.
Battery-Powered Heater:
The Chemical energy store (in the battery) decreases.
The Heat (Thermal) energy store increases.
Energy is transferred Electrically.
Remote Control Car (Battery to Motor):
The Chemical energy store in the battery decreases.
The Kinetic energy store in the motor increases.
Energy is transferred Electrically.
Lifting a Box onto a Shelf:
The Kinetic energy store of the box (as it is moved) decreases once it stops at the height.
The Gravitational Potential energy store increases.
Energy is transferred Mechanically.
The Sun to the Earth:
The Nuclear energy store of the Sun decreases.
The Thermal energy store of the Earth increases.
Energy is transferred via Radiation.
Heating a Pan of Water over a Campfire:
The Chemical energy store of the fuel decreases.
The Heat (Thermal) energy store of the water increases.
Energy is transferred by Heating.
Winding up a Toy Car:
The Kinetic energy store (from the person winding) decreases.
The Elastic Potential energy store (in the internal spring) increases.
Energy is transferred Mechanically.
Releasing a Wound Toy Car:
The Elastic Potential energy store decreases.
The Kinetic energy store increases.
Energy is transferred Mechanically.
Throwing a Ball up through the Air:
The Kinetic energy store decreases.
The Gravitational Potential energy store increases.
Energy is transferred Mechanically.
A Jack-in-the-Box Opening:
The Elastic Potential energy store (in the spring) decreases.
The Kinetic energy store (of the figure) increases.
Energy is transferred Mechanically.
Battery-Powered Hand-Held Fan:
The Chemical energy store decreases.
The Kinetic energy store (of the blades) increases.
Energy is transferred Electrically.
Machine Pushing Boxes Along the Ground ( total):
Useful: is transferred mechanically to move the boxes.
Wasted: () is transferred as heating due to friction.
Outcome: The wasted energy is dissipated to the surroundings.
Checking for Understanding (Pathway Identification)
Computer Switched On: Energy is transferred Electrically.
Beaker of Water Heated by Bunsen Burner: Energy is transferred by Heating.
Apple Falling from a Tree: Energy is transferred Mechanically (due to gravitational force).
Light Bulb Being Seen: Energy is transferred by Radiation (light waves).
Guitar Being Heard: Energy is transferred by Radiation (sound waves).
Hands Rubbed Together: Energy is transferred Mechanically (via friction, though it results in a heat store increase).