Science 10

1. Science 10 • Aim: Efficiency, Energy and us.

2. Agenda • Efficiency, Energy and us • Study Guide – Homework • Quizzes back on Monday • Next class

3. Useful Energy and Efficiency • The initial energy source applied to a machine is called the energy input (think electricity) • The desired energy needed to do work is called the useful output energy • The work done by the machine is called the useful work output • Energy and work that is not useful are called waste energy and waste work

4. Efficiency • A measurement of how effective a machine is at converting energy input into useful energy output. Car engine efficiency = 12-15% Electric engine = Up to 95% Steam reciprocal engine = 50-75% Steam turbine engine = Up to 40%

5. Conversion of total mechanical energy to useful mechanical energy Or

6. Question • A crane lifts a load of construction materials from the ground to the second floor of a building. In the process, the crane does 2.30 x 104 J of work or mechanical energy input, while doing 8.00 x103 J of useful work or mechanical energy output in lifting the load. What is the mechanical percent efficiency of the crane?

7. Transfer of total thermal energy to useful thermal energy In heating a pot of water, 2.00x103 J of heat was supplied by the stove element. If only 5.00x102 J of heat was actually gained by the water (heat output), what was the percent efficiency of the stove element?

8. Conversion of total thermal energy to useful mechanical energy or vice versa For devices that convert heat to mechanical energy use For devices that convert mechanical energy to heat use

9. Energy Applications Energy supply broken down into two types • Solar energy sources • Non-solar energy sources Renewable and Non-renewable Energy sources • Renewable – Continually and infinitely available. • Non-renewable – limited an irreplaceable

10. Energy Demand Historically, our ancestors used only renewable resources like solar energy wood or biomass. This is only a fraction of what is used today. There is a high demand placed on energy sources now. • Amount of energy used per person has increased exponentially • The world population has increased as well. • Many societies use non-renewable resources rather than renewable resources.

11. The effects of energy use • The high demands of fossil fuels has led to a strain on existing supplies • Searching for and extracting new supplies have led to damaging effects on the ecosystem.

12. Energy Consumption and Conservation At the rate we are using oil, coal, and natural gas, it is projected that our supply will run out in ~40, ~216, and ~62 years respectively. • Decreasing the rate at which we use these fuels does not stop the problem, but only delays the result.

13. Alternative Energy Sources • Switching Energy Sources is an alternative to using all of the fossil fuels up. • Unfortunately this is very expensive, and is difficult to implement into society. • Until we find an alternative source, our best bet is to conserve what we have now.

14. Cogeneration • The process in which industries use the waste material from one process to power a second process. • Ex. Using the steam from thermal power stations to heat nearby buildings before being heated again in the thermal power station.

15. How could you conserve energy? • Turn off unused appliances • Turn down thermostat (where more clothes) • Car pool, or take public transport • Avoid energy wasting appliances and gadgets. • Reduce water consumption (in shower, sink, watering lawns, etc..)

16. Sustainable Developement • Economic Development that meets current needs without compromising the ability of future generations to meet their needs.