4.1.1 P1 Energy changes in a system (will come up) Flashcards
What are all the energy stores
Kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, magnetic, nuclear
What happens when a system changes
Energy is transferred, there is a change in the way the energy is stored
eg an arrow fired from a bow, a kettle heating water
Ways energy can be transferred
Mechanically (work done by a force eg pushing, pulling, stretching)
Electrically (a charge (current) moving through a pd eg charges moving round a circuit
Heating (energy transferred from a hotter object to a colder object eg heating a pan of water on a hob)
Waves (light and sound eg energy from sun reaching earth by light)
Main uses of energy resources
Heating - natural gas used to heat radiators, coal in fireplaces, solar power
Generating electricity
Transport - petrol and diesel created from oil
Definition of specific heat capacity
The amount of energy required to raise the temperature of 1kg of a substance by 1 degree
What are the units for specific heat capacity
J/kg °C
How does energy transfer in a kettle
Energy is transferred to the water from the kettle’s heating element by heating, to the water’s thermal energy store (causes the temperature to rise)
How is energy transferred when a ball is thrown upwards
The initial force exerted by a person to throw the ball upwards does work
Energy is transferred from the chemical energy store of the persons arm to the kinetic energy store of the arm and ball
How is energy transferred when a car slows down
Friction between a cars brakes and its wheels does work
Energy is transferred from the cars wheels kinetic energy stores to thermal stores of the brakes and surroundings causing it to slow down
How is energy transferred between a collision of a car and a stationary object
The contact force between the car and object does work
Energy is transferred from the cars kinetic energy store to other stores eg thermal, elastic potential
Some energy will also be transferred away by sound waves
Conservation of energy principle
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed
What is power
The rate at which energy is transferred
Example of comparing power
two electric motors that both lift the same weight through the same height but one does it faster than the other
Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position. Ignore air resistance.
● Upwards: KE is converted to GPE
● Peak: Maximum GPE, zero KE
● Downwards: GPE is converted to KE
Describe the energy transfers for a bungee jumper.
● When falling, the GPE is converted to KE of jumper
● As the cord tightens, KE is converted and stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s initial GPE equals the EPE stored in the cord
