1. C-11 Energy Systems Energy Transformation and Power Physics 2015

2. The workings of the universe can be viewed as energy flowing from one place to another and changing back and forth from one form to another.

3. Law of Conservation of Energy As energy takes different forms and changes things by doing work, nature keeps perfect track of the total. No new energy is created and no existing energy is destroyed.

4. Energy in a closed system The conservation of energy is most useful when it is applied to a closed system. Because of the conservation of energy, the total amount of matter and energy in your system stays the same forever.

5. Energy in a closed system The total energy in the system is the potential energy of the ball at the start. Later, the ball is at a lower height (h) moving with speed (v) and has both potential and kinetic energy.

6. 11.1 Efficiency Efficiency is defined for a process. A process is any activity that changes things and can be described in terms of input and output. The efficiency of a process is the ratio of output to input.

7. EFFICIENCYEFFICIENCY Efficiency Efficiency is defined as the ratio of output work to input work. An ideal machine has equal output and input work (W o /W i = 1) and its efficiency is 100%. Real machines have efficiencies less than 100% because not all of the force is transferred into energy. (There is always friction somewhere)

8. Calculate efficiency 1.A pulley system lifts a 1400 N rock a distance of 1.2 m. A force of 365 N is exerted and the rope is pulled 4.8 m. a)What is the work input? b)What is the work output? c)What is the efficiency?

9. 11.1 Efficiency Efficiency can also mean the ratio of energy output divided by energy input.  = E o E i Energy output (J) Energy input (J) Efficiency

10. Example of Real Machine & Efficiency The work output is reduced by the work that is converted to heat, resulting in lower efficiency.

11. 11.1 Efficiency The work output is reduced by the work that is converted to heat, resulting in lower efficiency.  According to the law of conservation of energy, energy cannot ever be lost, so the total efficiency of any process is 100%.

12. 11.1 Efficiency in natural systems  Energy drives all the processes in nature, from winds in the atmosphere to nuclear reactions occurring in the cores of stars.  In the environment, efficiency is interpreted as the fraction of energy that goes into a particular process.

14. 11.1 Efficiency in biological systems  In terms of output work, the energy efficiency of living things is typically very low.  Almost all of the energy in the food you eat becomes heat and waste products; very little becomes physical work.

15. 11.1 Estimating efficiency of a human The overall energy efficiency for a person is less than eight percent. An average person uses 55–75 kilocalories per hour when just sitting still. The rate at which your body uses energy while at rest is called your baseline metabolic rate (BMR).

16. Efficiency in biological systems  Since processes in the universe almost always lose a little energy to friction, time cannot run backward.  If you study physics further, this idea connecting energy and time has many other implications.

17. Power It makes a difference how fast you do work.

18. POWERPOWER Power is the rate of doing work. Unit of measurement: – Watt (W)= one joule of energy transferred in one second (J/s) – 1000 W = 1 kW (Remember):

19. Power  A unit of power is called a watt.  Another unit more familiar to you is horsepower.  One horsepower (the avg. power output of a horse) is equal to 746 watts.

20. Power in human technology You probably use technology with a wide range of power every day. Machines are designed to use the appropriate amount of power to create enough force to do work they are designed to do.

21. Power in natural systems Natural systems exhibit a much greater range of power than human technology The sun has a total power output of 3.8 × 10 26 W. The power received from the sun is what drives the weather on Earth.

22. Energy flow in systems Energy flows almost always involve energy conversions. To understanding an energy flow: 1.Write down the forms that the energy takes. 2.Diagram the flow of energy from start to finish for all the important processes that take place in the system. 3.Try to estimate how much energy is involved and what are the efficiencies of each energy conversion.

23. 11.3 Energy flow in systems A pendulum is a system in which a mass swings back and forth on a string. There are 3 chief forms of energy: potential energy, kinetic energy, and heat loss from friction.

24. 11.3 Energy flow in human technology The energy flow in technology can usually be broken down into four types of processes: 1.Storage ex. batteries, springs, height, pressure 2.Conversion ex. a pump converting mechanical energy to fluid energy 3.Transmission ex. through wires, tubes, gears, levers 4.Output ex. heat, light, electricity

25. 11.3 Energy flow The energy flow diagram for a rechargeable electric drill shows losses to heat or friction at each step.

26. Energy flow in natural systems The energy flows in technology tend to start and stop. Many of the energy flows in nature occur in cycles. Water is a good example.

28. Energy flow in natural systems A food chain is a series of processes through which energy and nutrients are transferred between living things. A food chain is like one strand in a food web. A food web connects all the producers and consumers of energy in an ecosystem.

29. Energy flow in natural systems The energy pyramid is a good way to show how energy moves through an ecosystem.

30. The production of electricity is not very efficient because there is so much energy lost as heat. When we use electricity, there is even more energy lost.