Energy Stores and Transfers

• System- object or group of objects
• When system changes, causes changes in the way energy is stored
• Eg: Roller coaster transfers energy between gravitational and kinetic energy; electric kettle transfers electrical to thermal
• Sankey Diagrams- Energy Input, Useful Energy Output, Energy Wasted

Equations-

Kinetic energy of moving object-                                                                                                kinetic energy = 0.5 x mass x (speed)2                                                                                 

Gravitational potential energy (raising object about ground level)-                                   gravitational potential energy = mass x gravitational field strength x height

Elastic energy stored in a stretched or compressed spring -                                                      elastic potential energy = 0.5 x spring constant x (extension)2

Kinetic Energy (Ek)-measured in Joules (j)..Gravitational Potential Energy (Ep)-measured in Joules (j)...Mass (M)-measured in kilogams (kg)...Speed (v)-measured in metres per second (m/s)...Gravitational Field Strength (g)-measured in newtons per kilogram (n/kg)...Height (h)-measured in metres (m)...Elastic Potential Energy (Ee)-measured in joules (j)...Spring Constant (k)- measured in newtons per metre (n/m)...Extension (e)- in metres (m)

• Internal Energy- total kinetic and potential energy of all particles that make up a system
• Work on a system increases energy stored in system
• Heating increases the energy of particles within a system causing it to change the energy stored
• When the energy increases, it can either increase the temperature or cause a change of state
• Specific Heat Capacity of substance- amount of energy required to raise temp of 1 kg of substance by one degree celsius

Factors that temperature increase depends on:

• Mass of substance heated
• What substance is
• Energy input

Change in thermal energy = mass x specific heat capacity x temperature change     Specific Heat Capacity (c)-measured in joules per kilogram per degree celsius (j/kg 'c)  Change in thermal energy (E)-measured in joules (j)

1. Use a Sankey diagram to illustrate the energy changes involved when a diesel powered crane is used to lift an object

2. Work out the energy required to heat 1.5kg of water from 20*C to 100*C. (c=4200J/kg *C)

3. Explain what is meant by 'reproducible' and why it is important.