Conservation of Energy

1. 01 September 2014 Conservation of Energy Keywords Wasted, dissipated, directly proportional, accuracy, precision.

2. Outcomes • All students should be able todescribe what the principle of conservation of energy is. • Most students should be able todescribe an example when, as energy is transformed it gets spread out and more difficult to use. • Some students should be able todescribe how to make the experiment more accurate and precise.

3. Braniac pendulum • http://www.youtube.com/watch?v=ZbCLAZSPLNk&p=CAB44595BDD39B39&playnext=1&index=5

4. Electricity Light + heat In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use. Describe the following energy changes and state the “waste” energy or energies: • A vacuum cleaner • A TV • A dynamo/generator Conservation of Energy In any energy change there is ALWAYS some “waste” energy: e.g. a light bulb:

5. Energy is measured in ………………(J) Energy cannot be created or destroyed. It can only be ……………… from one form to another form. • In other words Energy is always…………... • When energy is transferred and/or transformed only part of it may be ………… transferred/ transformed, the rest is ……………. • Energy will eventually be transferred to the ……………… which will get ………….. Joules surroundings conserved usefully wasted transformed warmer

6. Practical Time!! Bungee jumping • Aim • To find out how much energy a bungee jumper loses in one jump as a percentage of their initial energy.

7. Bungee!!!! • http://www.youtube.com/watch?v=lAZIxuxjogI

8. Part 1 • In one jump, a bungee jumper starts and finishes with gravitational potential energy. • The change of gravitational potential energy of a bungee jumper is proportional to the change of height between the lowest and highest position. • Use a suitable object on an elastic band as the bungee jumper. • Repeat your test several times to check the reliability of the measurements. Record all your measurements in a table. • Use your measurements to work out the percentage of the initial energy the jumper has after one complete jump.

9. Bungee Jump PracticalAnalysis and Evaluation • Part 3 • Draw an energy transfer diagram for the Bungee Jumper. • Explain the energy changes that take place during one complete jump and what type of energy is lost. • Part 4 • Evaluate experiment by explaining how the method or equipment used could be changed to make it more accurate and precise.

10. Plenary - The Big Q: how can we improve accuracy and precision? • A lightbulb maker claims that its 100 Watt bulb gives off 20 Joules of light per second. The student uses the set up below to heat up some water and measure the change in temperature of water over a ten minute period to calculate the heat energy it gives off. thermometer From her calculations, she finds that the water receives 50 Joules of Heat energy every second. All: What is the conservation of energy? Most: Why does she measure the heat given off, when the claim was made about light? Explain by using the conservation of energy. Some: Look at the student’s experiment; describe how she could have changed it to make her results more accurate. What could she have done differently to make the experiment more precise?