P1: Conservation and Dissipation Flashcards
What are the types of energy stores?
Chemical - fuels, foods or chemicals in batteries. Energy transferred during chemical reactions.
Kinetic - energy an object has because it is moving.
Gravitational Potential - energy stored in object because of its position due to gravity.
Elastic Potential - energy stored in a springy object when it is stretched/squashed.
Thermal - energy of a substance due to its temperature.
How can energy be transferred?
By heating, waves, electric current or when a force moves an object.
What are closed systems?
Systems that do not allow transfer of matter into or out of the system. No energy transfers take place into or out of energy stores in the system, however energy can be transferred within stores of a closed system.
What is the Law of conservation of energy?
Energy cannot be created or destroyed. This means the total energy of a system is always the same before and after transfers.
What is the equation for work done?
Work Done = Force Applied x Distance
Energy Transferred = Work Done
How is work done on an object? Give an example.
When an object is moved by a force, work is done on the object so transfers energy to the object.
E.g. work done to overcome friction is transferred as energy to thermal energy stores of objects rubbing together and the surroundings.
What is the equation for gravitational potential energy?
Change in Gravitational Potential Energy Store= Mass x Gravitational Field Strength x Height
How does gravitational potential energy increase?
As an object moves upwards gravitational potential increases because work is done to overcome gravity force. The work done depends on the objects weight (force) and its height (distance).
What is the equation for kinetic energy?
Kinetic Energy = 1/2 x Mass x Speed^2
What is the equation for elastic potential energy in a stretched spring?
Elastic Potential Energy = 1/2 x Spring Constant x Extension^2
Only when work is done on object.
What is useful energy?
The energy transferred to where it is wanted in the way it is wanted.
What is wasted energy? Give an example.
It is energy not usefully transferred, it is dissipated to the surroundings and gets less and less useful.
E.g. Gears of a car get hot because of friction, energy transferred from kinetic energy of gear box (useful) to thermal energy stores (wasted) and surroundings.
What is the equation for efficiency?
Efficiency = Useful Output Energy / Total Input Energy x 100
How could you improve efficiency?
Lubricate moving parts to reduce friction, use wires with low electrical resistance so that it doesn’t heat up, streamline shapes.
What is the equation for power?
Power (W) = Energy Transferred / Time Taken
