Conservation of Energy Flashcards
What is the principle of the conservation of Energy?
Energy cannot be created or destroyed. It is just moved from one store to another.
What is efficiency?
A measure of how good a device is at changing enrergy from one store to a useful store.
Caculation of efficiency
Useful output energy / total input energy
What is work?
Moving an objected requires a force being applied. Work is done on the object when a force transfers energy.
Change of GPE (Gravitational Potential Energy) calculation
Mass x Gravitation Field strength x Change of height
Work calculation
Work done = Force x Distance
What is kinetic energy?
Energy an object has while moving.
Kinetic Energy calculation.
1/2 x mass x velocity ^2 (velocity squared)
Why is the efficiency of a device always less than 100%?
There will always be wasted energy.
How to calculate ELastic Potential Energy of an object?
1/2 Ke^2
K= spring constant
e^2= extension squared (m)
What is a lightbulb’s useful energy and wasted energy?
Useful: Light
Wasted: Thermal
What is a hairdryer’s useful energy and wasted energy?
Useful: Thermal transferred to hair
Wasted: Thermal transferred to hairdryer and surroundings. Sound.
What is Energy dissipation?
A term that often is used to describe ways in which energy is wasted.
How to calculate Power?
Energy/ Time
What happends to wasted energy?
It is transferred to the surroundings
What is ‘Specific Heat Capacity’ of a substance?
The amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree Celsius.
Units for Specific Heat Capacity?
Joules, degrees celcius and kilograms
What is the definition of Power?
The rate of which energy is transferred or work done
Give 2 equations for Power
Energy/ time
Work done/ time
WHAT is the unit of Power?
Watt (W)
Two motors lift the same mass through the same height. Motor A does this in
half the time of Motor B. Which dissipates the most power?
Motor A. The energy transferred is the same but the time taken is less
Describe the energy changes involved when a ball is thrown upwards and then
returns to its starting position. Ignore air resistance.
Upwards: KE is converted to GPE
Peak: Maximum GPE, zero KE
Downwards: GPE is converted to KE
Describe the energy transfers for a bungee jumper.
Falling, the GPE is converted to KE of jumper
Cord tightens, KE is converted and stored as Elastic Potential Energy.
Lowest point, the jumper’s initial GPE = EPE stored in the cord
Give examples of chemical energy stores.
Food, batteries and fuel
