Energy (P1,P2,P3)

Energy Stores and Systems.

A system is an object or group of objects. 

When a system changes, there aree changes in the way energy is stored. 

Calculating Energy Changes.

Kinetic Energy (J) = 0.5 x mass (kg) x (speed)^2 (m/s)

GPE (J) = mass (kg) x gravitational field strength x height 

Elastic Potential Energy (J)  = 0.5 x spring constant (N/m) x (extension)^2 (m)

Internal Energy.

Internal Energy is the total kinetic and potential energy of all the particles that make up a system.

Doing work on a system increases the energy stored in a system.

Heating changes the energy stored in a system by increasing the energy of the particles within it.

As the energy increases, this will either increase the temperature or produce a change of state. 

If the temperature increase, the increase depends on:

• The mass of the sustance heated.
• What the substance is.
• The energy input.

The Specific Heat Capacity.

The specific heat capacity of a is the amount of energy required to raise the temperature of one kg of a substance by one degree celsius.

Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg *C) x temperature change (*C)

The amount of energy stored can also be found by the amount of work done:

Work done = force x distance 

Energy Transfers.

Energy can be transferred usefully, stored or dissipated (spread out to the surroundings)

Engery cannot be created or destroyed.

In a closed system the energy never changes, but can be transferred from one store to another.

Wasted energy is caused by unwanted energy transfers. These can reduced in several ways:

• Lubrication - reducing the friction that produces heat.
• Thermal insulation - reduces heat loss.
• Tightening loose parts - prevents unwanted vibration that wastes energy as sound.

Energy Transfers.

The rate of cooling depends on the thickness and thermal conductivity of the walls of a building.

Thin walls with high thermal conductivity will conduct heat the quickest, cooling a building down rapidly.

Key Point.

An anomalous result is one that doesn't fit a pattern. These:

• Should be looked at to try and determine the cause.
• Should be ignored when plotting graphs.
• Should not be included when calculating averages.

Situation:

• An object projected upwards.
• An object hitting an obstacle.
• A car accelerating.
• A car braking.
• Water boiling in a kettle.

Energy Transfers:

• Kinetic energy (initial movement of object) to GPE (increase in height).
• Kinetic energy (moving object) to thermal energy and sound (when object hits obstacle).
• Chemical energy (in the fuel) to kinetic energy (movement of car).
• Electrical energy to thermal energy.
  

National and Global Energy Resources.

• Biofuel (Renewable) - Transport and electricity generation.
• Wind (Renewable) - Electricty generation.
• Water (Renewable) - Electricty generation.
• Geothermal (Renewable) - Electricty generation and heating.
• Tidal (Renewable) - Electricty generation.
• Solar (Renewable) - Electricty generation and some heating.
• Nucleur Fuel (Non-renewable) - Electricty generation and some military transport.
• Coal (Non-renewable) - Electricty generation, heating and some transport.
• Oil (Non-renewable) - Transport and heating.
• Gas (Non-renewable) - Electricity generation, heating and some transport.