Power and Efficiency

1. Power and Efficiency • Power = work done (or energy change) / time interval • Two cars accelerate from rest to highway speed • One does it in five seconds (Porsche) • One does it in ten seconds (4 cylinder SUV) • Which uses more power? • Efficiency = useful energy output / Total Energy Input • At best 30-35% of the Chemical Energy in gas => Moving a carCar engines are at best 30-35% EfficientElectric motors can have efficiencies approaching 99% Slide 10-23

2. Energy And Real Life • Tour de FranceA Tour de France bicycle racer needs to eat 8000 calories per day to maintain their weight. About 65-70% of this energy is used to maintain body temperature. • Bow and ArrowsAbout 60-75% of the PE in a drawn bow goes into the KE of an Arrow. The rest of the energy heats the bow. • Guns and BulletsOnly about 30% of the energy in a firearms discharge is transferred to the projectiles they fire Slide 10-23

3. Compare Energy and Momentum

4. Questions for Einstein’s Big Idea What did Michael Faraday discover that affects our every day lives How did the Lavoisier’s demonstrate conservation of mass? How did Madame de Chatelet show that Energy is proportional to v2 What does E = mc2 mean? How would you explain it to your friends? How did Lise Meiner and associates validate E = mc2 What are some applications of E=mc2

5. Questions for Einstein’s Big Idea What was the most interesting thing you learned about from watching the DVD? What do thing was the most important thing you learned from the DVD? Should I show this DVD to my next Physics 102 class? Why or why not?

6. Building on Einstein’s Big Idea Magnetic field from a wire How a magnetic field creates electricity Eddy Currents

7. Building on Einstein’s Big Idea and Beyond Frames of Reference Special Relativity Photoelectric Effect Dark Matter Dark Energy Global Warming