Conservation and Dissipation of Energy (C1)
Energy Stores and Systems
Energy is never used up, rather transferred between energy stores
Energy Stores hold energy transferred into an object
Energy Stores to Know
Thermal
Kinetic
Gravitational Potential
Elastic Potential
Chemical
Magnetic
Electrostatic
Nuclear
Includes fuel, food, or chemicals found in batteries
Energy an object has because its moving
The energy stored in an object because of its position above the ground
The energy an object has because of its temperature
When a system changes, energy transfers
A system is a word for a single object or group of objects
When a system changes, energy is transferred
It can be transferred through different objects in the system or different energy stores
Closed systems are systems where matter and energy cannot enter or leave
The net change in energy of a closed system is always zero
Energy Transferred by Heating
Example a kettle boiling the water
The water is the system and the energy is being transferred from the kettle to the water (water is heated)
The energy is stored in the waters thermal energy store causing temperature to rise
The kettle's heating could also be classed as a two-object system
Energy is transferred electrically to the thermal store of the kettle
This is then transferred by heating to the waters thermal energy store
Energy Transferred by Doing Work
Work can be done when a current flows or by a force moving an object
The initial force from a person to throw a ball upwards is work
It causes energy to transfer from chemical energy in a persons arm to kinetic energy of a ball
A ball dropped from a heigh is accelerated by gravity
The gravitational force does work
Causes energy to transfer from balls gravitational potential energy store to its kinetic energy store
The friction between a cars brakes and wheels does work as it slows
It causes kinetic energy store from the wheels to transfer to chemical energy store of the sorroundings
In a collision between a car stationary force, the normal contact force between the car and object does work
It causes energy from the cars kinetic energy to be transferred to surrounding stores such as elastic potential and thermal energy stores of the object and car body
Some energy can also be transferred away by sound waves
Kinetic and Potential Energy Stores
Kinetic Energy
Anything that is moving has a kinetic energy store
If an object speeds up, energy is transferred to this energy store and if it slows down energy is transferred away from this energy store
The energy in the kinetic energy store of an object is proportional to its mass and speed
The formula for kinetic energy is
Eₖ = mv²
Potential Energy
Gravitational Potential Energy
Lifting an object in a gravitational field requires work
This means by lifting an object higher, you are transferring more energy into the gravitational potential energy of an object
The energy inside the GPE of an object is proportional to its mass, height and the strength of the gravitational field
The equation for GPE is
Eₚ = mgh
Specific Heat Capacity