Energy Stores Flashcards
How is energy transferred in a kettle
Energy transferred electrically to the thermal energy store of the kettle which transfers water heating the waters thermal energy store
Electric-> heat + sound
What is work done
Energy transferred when a current flows or by a force
Examples of work done
Throwing a ball: chemical energy store of persons arm to kinetic energy store of ball and arm
Object moving upwards: kinetic-> gravitational +heat
Car accelerating : kinetic + heat
Slowing down : kinetic energy of wheels-> heat+ sound
Objects colliding : kinetic energy-> heat+sound
Falling objects: gpe-> kinetic+ heat
Kinetic energy
Anything that is moving has energy in its kinetic energy store energy is transferred to the store when the object speeds up
Kinetic energy(J)= 1/2 x mass (kg) x v2 (m/s)
Gravitational potential energy
Lifting an object in a gravitational field requires work this causes a transfer of energy to the gravitational potential energy store of the raised object
GPE= mass(kg) x gravity(10m/s2) x height (m)
As an object is raised it gains gpe
Ball falling
As object increases in speed more gpe converts into kinetic. Just before reaching the floor the gpe is minimum. Kinetic energy is max therefore the speed is the max
As the ball hits the floor it loses energy to sound and heat the ball will bounce back up due to elastic energy but will never reach the original height
Elastic potential energy
Stretching or squashing an object can transfer energy to its elastic potential energy store . As longs the limit of proportionality has not been exceeded
E= 1/2 x spring constant (N/m) x extension 2 (m)
Specific heat capacity
How hard it is to heat something up
How much energy a substance can store
AMOUNT OF ENERGY NEEDED TO RAISE THE TEMPERATURE OF 1kg OF A SUBSTANCE BY 1degrees C
Energy transferred= mass(kg) x shc(J/kg degrees C) x change in temperature (degrees C)
Conservation of energy
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed
Dissipation
Wasted energy spreads into surroundings becomes less useful and heats the surroundings
E.g. mobile phones
Friction
How can friction be reduced
Lubricating
Moving parts reduces friction which reduces heat transfer
Thermal insulation
Reduce and increase heat transfer as needed e.g. Black is a good emitter and absorbs heat energy
White reflects heat energy - poor absorber and emitter
High thermal conductivity
Materials with high thermal conductivity allow heat transfers easily by conduction
Conduction
Transfer of energy in a solid as particles vibrate gain kinetic energy and collide with neighbouring particles
Thin walls - short heat path
Thick walls - more material harder for heat to escape
Efficiency
Is never 100 or more than 1
