Energy stores and systems Flashcards
- When energy is transferred to an object, the energy is stored in one of the objects following energy stores
1) Thermal energy store
2) kinetic energy store
3) gravitational potential energy store
4) Elastic potential energy store
5) Chemical energy store
6) Magnetic energy store
7) electrostatic energy store
8) nuclear energy store
How is energy transferred ?
mechanically, electrically by heating or by radiation
What is a system ?
What occurs as a system changes ?
- a single objects or group of objects you’re interested in.
- energy is transferred into or away from system, between different objects in the system or between different types of energy store
What are closed system ?
systems where neither matter nor energy can enter or leave.
The net change in the total energy of a closed system is always zero.
Energy can be transferred by heating
Example of boiling water in a kettle - think of water as system. Energy transferred to water by heating, into waters thermal energy store.
You can also think of the kettle’s heating element and the water as two object systems. Energy is transferred electrically to thermal energy store of the kettles heating element which transfers energy by heating to the waters thermal energy store.
Energy can be transferred by doing work
doing work = energy transferred
Work can be done when current flows or by a force moving an object
Examples of doing work
Initial force exerted by a person to throw a ball upwards does work. Causes energy transfer from chemical energy store of persons arm to kinetic energy store of ball and arm.
Ball dropped from height is accelerated due to gravity. The gravitational force does work. causes energy to be transferred from balls gravitational potential energy store to its kinetic energy store
Examples of doing work
The friction between a car’s brakes and its wheels does work as it slows down. Causes energy transfer from wheels kinetic energy store to thermal energy store of surroundings.
In a collision between a car and a stationary object. The normal contact force between car and object does work. causes energy to be transferred from cars kinetic energy store to other energy stores such as elastic, thermal energy store of object and car body. Some energy might be transferred away by sound waves.
