Energy Flashcards
(36 cards)
What is an energy system
A group of objects that have the ability to do work
What is the rule of conservation of energy?
Energy cannot be created or destroyed so when work is done, energy from one store is carried along a party way to another store
All the energy stores and examples
- Chemical - food, fuel, batteries
- Kinetic- in moving objects
- Gravitational Potential - raised objects
- Elastic Potential - stretches, compressed or twisted objects
- Internal (Thermal) - in any heated object
- Magnetic- any object with a magnetic field
- Electrostatic - in electrostatic forced between charges
- Nuclear - forces acting between atomic nuclei
Force Pathways
- Mechanically - when a force acts on and moves an object
- Electrically - when an electric current flows
- Heating - a temperature difference between objects
- Radiation - electromagnetic waves or sound
What is energy measured in
Joules
- 1 kJ = 1000J
- 1 megajoule = 1000,000J
Equation for energy change (mechanical work)
Mechanical work is the amount of energy transferred by a force.
Work(J)=Force(N) x Distance (m)
When is electrical work done
electrical work is done when charge flows in a circuit
Energy Transferred equation
Energy transferred/Work(J) = charge flow (Q) x Potential difference (V)
Kinetic energy equation
Moving objects have kinetic energy: Kinetic energy (J) = 0.5 x Mass(kg) x Speed^2 (m/s)
What objects have elastic energy
Stretched or bent objects have elastic energy if they have the ability to recover to their original shape and dimensions. When a weight(force) is added to a spring, it extends and the spring now has a store of elastic potential energy which will be released if weight is removed.
Equation for elastic potential energy
Elastic Potential Energy = 0.5 x spring constant (N/m) x extension^3
Ee = 0.5ke^2
How does an object gain Gravitational Potential energy
When an object is raised above the ground level it gains Gravitational Potential Energy. This stored energy can be released if the object is allowed to fall
Gravitational Potential energy equation
G.P.E (J) = Mass (kg) x Gravitational field strength (N/kg) x height (m)
Ep = mgh
When does the thermal (internal) energy store in a system change
The thermal (internal) energy store in a system changed if its temperature changes.
What happens to metal when heated in a furnace? What does the amount of energy gained depend on?
When metal is heated in a furnace the thermal energy store increases.
The amount of energy gained depends on the mass of the metal, how much the temperature increases and the specific heat capacity of the metal
What is the specific heat capacity
The amount of energy required to raise the temperature of a 1kg substance by 1C
Equation for change in thermal energy (specific heat capacity)
Change in thermal energy (J) = mass(kg) x specific heat capacity (J/kgC) x temperature change (C)
E=m x c x O
What is power
Power is the rate at which energy is transferred or the rate at which work is done
what is power measure in
It is measured in Joules/second
1J/s = 1 Watt
It is measured in watts
equation for power (energy transferred)
Power (W) = Energy transferred (J) / Time (s)
equation for power (work done)
Power (W) = Work done (J) / time (s)
Work done = force x distance
What can and can’t happen to energy
Energy can be transferred usefully, stored or dissipated but cannot be created or destroyed
What happens in a closed energy system
In a closed energy system there is no change to the total energy in a system and all energy can be accounted for, even when energy stores change
what is unwanted energy often described as
unwanted energy is often described as wasted energy. Unwanted energy transfers result in energy stores that are not useful
