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P1 Conservation and Dissipation of Energy (Changes in Energy Stores (When…
P1 Conservation and Dissipation of Energy
Changes in Energy Stores
When an object falls and gains speed, its store of GPE decreases and it's kinetic energy store increases
When a falling object hits the ground without bouncing back, its KE store decreases
Energy is transferred by heating, by waves, by electric current or by a force when it moves an object
Some or all of its energy is transferred to the surroundings - the thermal energy store of the surroundings increases and energy is also transferred by sound waves
Energy can be stored in a variety of different energy stores
Conservation of Energy
A closed system is a system in which no energy transfers take place out of or into the energy stores of a system
Energy can be transferred between energy stores within a closed system
Conservation of energy applies to all energy changes
The total energy of the system is always the same before and after any transfers
Energy can't be created or destroyed
Energy and Work
Work done = force x distance
Work done to overcome friction is transferred as energy to the thermal energy stores of the objects that rub together and the surrondings
Energy transferred = Work Done
Work is done on an object when a force makes the object move
Gravitational Potential Energy Stores
GPE = mass x gravitational field strength x height
The gravitational field strength at the surface of the Moon is less than on Earth
The GPE store of an object increases when it moves up and decreases when it moves down
Kinetic and Elastic Energy Stores
Elastic potential energy is the energy stored in an elastic object when work is done on the object
EPE = 0.5 x Spring Constant x Extension^2
KE = 0.5 x Mass x Velocity^2
The energy in the kinetic energy store of a moving object depends on its mass and its speed
Energy Dissipation
Wasted energy is eventually transferred tot he surroundings which become warmer
As energy dissipates it gets less and less useful
Wasted energy is the energy that is not useful energy and is transferred by an undesired pathway
Useful energy is energy in the place we want it and in the form we need it
Energy and Efficiency
Machines waste energy because of friction between their moving parts, air resistance, electrical resistance and noise
Machines can be made more efficient by reducing the energy they waste
No energy transfer can be more than 100% efficient
The efficiency of a device = useful energy transferred / total energy supplied to the device x 100
Energy and Power
Efficiency of an appliance = useful power out / total power in x 100
Power wasted by an appliance = total power input - useful power output
Power = Energy transferred / Time
Power is rate of transfer of energy
Electrical Appliances
Uses of everyday electrical appliances include heating, lighting, etc.
An electrical appliance is designed for a particular purpose and should waste as little energy as possible
Electrical appliances can transfer energy in the form of useful energy at the flick of a switch
Electricity and gas and/or oil supply most of the energy you use in your home