Conservation and dissipation of energy (Changes in energy stores (Energy…
Conservation and dissipation of energy
Changes in energy stores
Energy is transferred by heat, force, waves or electrical currant
When an object falls it's stores of Gravitational potential energy decreases and its stores of kinetic energy increases
Energy is neither created or destroyed
Thus means when a object loses energy it is either transferred to another source or the surroundings via heat and sound.
Energy can be transferred from one store to another. Eg a ball falling from GPE (gravitational Potential energy) to Kinetic energy and finally to thermal when it hits the ground.
Gravitational Potential Energy (GPE) - an object above the ground
Elastic potential energy (EPE) -stretched or squashed
Kinetic energy - moving object
Thermal Energy - heat
Chemical energy - From food and cell
Conservation of energy
A closed system is a isolation system where no energy is transferred out or in the system. Energy can be transferred within a closed system though.
A swing would keep swinging for ever if not for air Resistance
Energy and work
Work done = Energy transfed
When work is done to over come friction energy is transferred to thermal energy.
The work done depends on the size of the force and the distance moved.
Friction at work.
If you rub your hands together they become warm. Your muscles work to overcome the friction between your hands. The work you do is transferred as energy that warms your hands.
Same again for a car when you apply the brakes. Energy is transferred from kinetic energy to thermal energy
When meteors form the air resistance causes friction upon them. The energy is transferred from GPE to kinetic energy, and then finally to thermal.
Gravitational potential energy
It increases with height and decreases with depth
It increases with height because work is done to increase its height
The Gravitational field strength is lower on the moon than on Earth.
When an object is moved upwards, the GPE is increased, and vice versa.
Useful energy is energy in the form we want when we need it
For example, when a plane takes of, the engines transfer energy from the chemical store. This increases the GPE and kinetic energy, this is useful energy. The rest , sound, is wasted energy.
Waste energy is energy that is not useful
It is transferred by a different pathway
As energy dissipates (spreads out) it get less useful
Energy and efficiency
The efficiency of a device = useful energy transferred by a device / the total energy supped to the device
No energy transfer can be 100% efficient
Machines waste energy because of their moving parts creating friction so some energy would be lost
Ways machines waste energy
Friction between moving parts causing heat
Lubricating moving parts
The resistance of a wire causes the wire to get hot
Use wires with little electrical resistance
Air resistance because of the force on a moving object that opposes its motion
Streamline the shapes of moving objects
Sound created by the machine
Cut out noise by tightening loose parts to reduce vibration
Electricity, gas and oil supply most of our energy
Electrical appliances can transfer useful energy at a flick of a switch
An electrical appliance is deigned to use as little energy as possible
In an old-fashioned clockwork radio, you wound up the spring to increase the EPE. The spring then unwinds, turning EPE into kinetic energy. This then goes into a small electric generator.
Energy and power
Power = rate of energy transferred
Efficacy of an appliance = useful power out / total power in
Power wasted = total power in minus useful power out