Conservation of Energy

1. Conservation of Energy 6A describe the law of conservation of energy;

2. Energy Basics • Energy • the ability to cause a change • The Conservation of Energy • Energy cannot be created nor destroyed, it can only be transformed • Examples of Energy • Light (electromagnetic) • Sun (solar energy – e.m.) • Heat (friction – e.m.) • Work (mechanical energy) • Gasoline (chemical energy) • Sound • Electricity

3. Potential Energy • Energy that is stored in an object relative to its position • FORMULA: PE = mgh • PE = potential energy • will be measured in Joules (J) • m = mass • will be measured in kilograms (kg) • g = gravity • will be measured in meters per second squared (m/s2) • h = height • will be measured in meters (m)

4. Kinetic Energy • Energy in the form of motion • FORMULA: KE = ½mv2 • In a closed system, the total energy in the system = PE + KE • TOTAL E = PE + KE

5. Kinetic Energy PE = 100% KE = 0% PE = 50% KE = 50% PE = 0% KE = 100%

6. Mechanical Energy • The total amount of energy in matter; both PE & KE • The KE comes from the vibration & movement of/between particles • The PE is determined by the forces that act within or between the particles

7. 1. According to the equation E = mc2, mass — • travels at the speed of light • can be transformed into energy • contains light energy • is doubled when exposed to light

8. 2. What is the approximate difference in gravitational potential energy of the two shaded boxes? • 19 J • 39 J • 59 J • 79 J

9. 3. Which process best shows the conversion of solar energy to chemical energy? • Prevailing winds causing windmills to spin • Green plants making their own food • Uranium producing heat to make steam • Tides generating electricity

10. 4. What is the potential energy of the rock? • 59,900 joules • 64,600 joules • 93,100 joules • 121,600 joules

11. 5. Which of the following is an example of solar energy being converted into chemical energy? • Plants producing sugar during the day • Water evaporating and condensing in the water cycle • The sun unevenly heating Earth’s surface • Lava erupting from volcanoes for many days

12. 6. Why is the sum of the products’ energy in this reaction less than the sum of the reactants’ energy? • Energy is given off as heat. • The products absorb available energy. • Energy is trapped in the reactants. • The reactants’ energy is less than the melting point of glucose.

13. 7. An inventor claims to have created an internal combustion engine that converts 100 kJ of chemical energy from diesel fuel to 140 kJ of mechanical energy. This claim violates the law of conservation of — • Momentum • Inertia • Energy • mass

14. 8. Assuming the chart contains all energy transformations in the Earth system, how much solar radiation goes toward evaporating water? • 40,000 terajoules • 92,410 terajoules • 121,410 terajoules • 133,410 terajoules

15. Fireworks Fireworks displays are often associated with celebrations. Some fireworks are rockets that can be fired into the air, producing colorful patterns of bright light. One rocket design involves a cardboard tube, a propellant, and a fuse. A cap on the tube contains metal salts and explosive powder with a second fuse. The propellant consists of a mixture of carbon (C), sulfur (S), and potassium nitrate (KNO3). Potassium nitrate is a potassium ion (K+) bonded to a nitrate ion (NO3–). A long cardboard tube is filled with the propellant. When a lit fuse ignites the propellant, the propellant releases oxygen, produces flames, and forces gas out the bottom of the rocket. These actions cause the rocket to rise high into the air. As the rocket reaches its maximum height, a second fuse ignites an explosion that heats and burns the metal salts. This heating and burning of metal salts produces large colorful flashes. Many people enjoy watching these colorful displays against the night sky. The use of fireworks can be dangerous. Professionals who use fireworks take many safety precautions while setting up and igniting the displays.

16. 9. As a rocket rises, its kinetic energy changes. At the time the rocket reaches its highest point, most of the kinetic energy of the rocket has been — • permanently destroyed • transformed into potential energy • converted to friction • stored in bonds between its atoms

17. 10. A motor produces less mechanical energy than the energy it uses because the motor — • gains some energy through motion • stores some energy as electrons • converts some energy into heat and sound • uses some energy to increase in mass