energy stores and systems

what is system

can be an object or a group of objects

types of energy stores

1. thermal

2. gravitational potential

3. elastic

4. magnetic

5. chemical

6. electrostatic

7. kinetic

8. nuclear-from breaking atoms apart

4 ways energy can be transferred

-mechanically-when force acts on an object

-heating- energy transferred from hotter to colder

-electrically- a charge moving through a potential difference

-radiation- energy transferred by electromagnetic waves

what is the overall change for a closed system

zero

energy transfer when an object is projected upwards

• Before the ball is thrown upwards, the person holding the ball has energy in their chemical store

• When the ball is thrown, some of that energy is transferred to the kinetic store of the ball as it begins to move upwards

• As the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store

energy transfer when a moving object hits an obstacle

• When an object, such as a car, is moving, energy in the chemical store of the fuel is transferred to the kinetic store of the car

• If the object hits an obstacle, such as the car hitting a wall, the speed of the car will decrease very quickly

  • Therefore, the energy in its kinetic store will decrease

• In this scenario, most of the energy from its kinetic store is transferred to the thermal store of the surroundings (dissipated)

• Energy is transferred mechanically to the thermal store of the wall (the force of the car on the wall)

• Energy is also transferred by heating to the thermal store of the car, the wall and to the thermal store of the air as the sound waves transfer energy away from the system (causing the air particles to vibrate) 

energy transfer when an object accelerated by a constant force

• When a vehicle is stationary, it has energy in the chemical store of the fuel

• When the vehicle speeds up or accelerates, the energy is transferred to the kinetic store of the car

energy transfer when vehicle slows down

• When a vehicle is moving, it has energy in its kinetic store

• As it slows down or decelerates, energy is transferred to the thermal store of the surroundings (dissipated)

• This energy is transferred by heating due to friction between the tyres on the ground, and due to friction between the brakes and the brake pads 

• Energy is also transferred by heating as the sound wavestransfer energy away from the system (making the air particles vibrate)

energy change when bringing water to a boil in electrical kettle

-electrical energy from plug socket flows to heating element of kettle where transferred electrically to thermal energy store of kettle’s heating element

-heating element transfers energy to the water’s thermal energy store

what is work done

energy transferred

2 types of work done

-work done by forces ( eg friction)

-work done when a current flows- energy required to overcome the resistance in the wires