P1. Conservation and Dissipation of Energy Flashcards
What are chemical energy stores?
Chemical energy stores include fuels, foods, or the chemicals found in batteries. The energy is transferred during chemical reactions
What are kinetic energy stores?
Stores that describe the energy an object has because it is moving
What are gravitational potential energy stores?
Stores that are used to describe the energy stored in an object because of its position, such as an object above the ground
What are elastic potential energy stores?
Stores that are used to describe the energy stored in a springy object when you stretch or squash it.
What are thermal energy stores?
Stores that describe the energy a substance has because of its temperature
What factors affect the amount of energy in the kinetic energy stores?
Mass and speed
What factors affect the amount of energy in the gravitational potential energy stores
Mass and height
What factors affect the amount of energy in the elastic potential energy stores
Spring constant, displacement, mass and material
What factors affect the amount of energy in the chemical energy stores
Object’s mass, chemical composition, the type of bonds that are present
What factors affect the amount of energy in the thermal energy stores
The mass of the object, the specific heat of the object and the change in temperature of the objeft
What is the principle of conservation of energy?
Energy cannot be created or destroyed
Why do forces cause heating effects?
As energy cannot be created or destroyed, the energy taken from the motion of the objects is converted in heat
What are closed systems?
A closed energy system is unable to exchange energy and matter with their surroundings
What are some examples of energy stores and systems?
Collision - A moving object will start off with kinetic energy. Once it hits an obstacle, the kinetic energy can be transferred to the surroundings as thermal energy and sound waves. Some of the kinetic energy can be transferred to the obstacle causing it to move
Flying - If a ball is projected upwards it will initially have kinetic energy. As the ball rises higher into the air, the kinetic energy will be transferred into gravitational potential energy. Once the ball reaches its highest point, the gravitational potential energy will all be converted into kinetic energy as the ball back into the ground
What is work?
Work is done on an object when a force makes the object move
Energy transferred = work done
What affects the work done by a force?
The size of the force and the distance moved
How do you calculate work done?
Work done (Joules) = Force applied (Newtons) × Distance moved along the line of action of the force s (metres)
Why do objects become heated by frictional forces
The presence of frictional forces means that some of the energy input is transferred into thermal energy. Seeing as more work is done due to frictional force anyway, there is a greater amount of energy transfer.
What does the work done depend on when an object moves up or down?
How far it is moved vertically
Its weight
How do you calculate the change in an object’s gravitational potential energy store?
change in an object’s gravitational potential energy store = weight × change of height
How do you calculate the change of gravitational potential energy store?
change of gravitational potential energy store Ep = mass, m × gravitational field strength, g × height, h
How do you calculate kinetic energy?
Kinetic energy, Ek = ½ x mass, m × speed², v²
How do you calculate elastic potential energy?
Elastic potential energy, Ee = ½ × spring constant, k × extension², e²
What happens to the energy transfer as an object rises?
Kinetic energy is converted to Gravitational Potential Energy (KE lost = GPE gained)
What happens to the energy transfer as an object falls?
Gravitational Potential Energy is converted to Kinetic Energy (GPE lost = KE gained)
What is useful energy?
Energy that is transferred to where it is wanted in the way it is wanted
What is wasted energy?
Energy that is not useful energy and is transferred by an undesired pathway, wasted energy is eventually transferred to the surroundings which become warmer
What happens as the energy dissipates
It gets less and less useful
Give an example of energy dissipation?
When the gears of a car get hot because of friction when the car is running. Here, energy is transferred from the kinetic energy store of the gear box to the thermal energy stores of the gear box and the surrounding air. The thermal energy stores of the gear box and the surrounding air therefore increase as do their temperatures.
How do you calculate efficiency?
(Useful output energy transferred by the device ÷ total input energy) x 100%
How do you reduce heating caused by friction between moving parts
Lubricate the moving parts
How do you reduce wires getting hot when a current passes through it due to the resistance of the wire?
In circuits, use wires with as little electrical resistance as possible
What is the comparison of energy use in electrical appliances?
Light bulb -
Useful energy: Light emitted from the glowing filament
Wasted energy: Energy transfer from the filament heating the surroundings
Electric heater -
Useful energy: Energy heating the surroundings
Wasted energy: Light emitted from the glowing element
Electric toaster -
Useful energy: Energy heating bread
Wasted Energy: Energy heating the toaster case and the air around it
How do you calculate power?
Power = energy transferred ÷ time take for energy to be transferred
How do you calculate efficiency with power?
Efficiency = useful power out ÷ total power in (x 100%)
How do you calculate power wasted?
Power wasted = total power in - useful power out
