P1 - Conservation and Dissipation of Energy Flashcards
How is energy stored?
Chemical energy stores - food, chemicals in batteries.
Kinetic energy stores - energy whilst moving.
Gravitational potential energy stores - energy stored in an object due to position, e.g. height above ground.
Elastic potential energy stores - energy stored in a springy object when it is squashed/stretched.
Thermal energy stores - energy a substance has due to temperature.
How is energy transferred?
Heating, by waves, by electrical current, or by force moving an object.
What is an energy transfer?
Energy moving from one type to another. Energy is never made or destroyed, so all energy is changed via energy transfer.
What is a closed system?
A system in which no energy transfers take place into or out of the energy stores in the system. Energy transfers can take place within the system, however.
What is work?
Work is done on an object when a force is applied to make the object move - energy transferred = work done.
How do we work out work done?
Work Done = Force Applied * Distance Moved Along Line of Action of Force
How does friction effect work done?
Work done has to overcome friction - work that acts to counter friction is not outputted as kinetic energy, but heat energy.
How does gravitational potential energy change as an object moves, and why?
As it moves higher, gravitational potential energy increases, as work done had to overcome the gravitational force, and vice versa.
How do we work out gravitational potential energy store changes?
Change of Gravitational Potential Energy Store = Mass * Field Strength * Change in Height.
How do we work out kinetic energy?
Kinetic Energy = 1/2 * Mass * Speed^2
How do we work out elastic potential energy?
Elastic Potential Energy = 1/2 * Spring Constant * Extension^2
What is useful/wasted energy?
Useful energy is energy in the place and form we need it. Wasted energy is energy that isn’t useful and is transferred down an undesired pathway. It spreads out to the surroundings.
How do we work out efficiency?
Efficiency = useful energy transferred by device / total input energy
How do machines waste energy?
Friction between moving parts, air resistance, electrical resistance, and noise. Machines can be made more efficient by reducing these factors, e.g. adding lube to reduce friction.
How do we work out power?
Power = Energy into appliance / Time taken for energy to transfer
