1. Energy Conversion and Conservation by new new

2. Science Journal Entry 24 Define potential and kinetic energy, record their formulas, and tell how these types of energies are different.

3. Energy Conversion Energy can be converted from one form to another. The process of changing energy from one form to another is called energy conversion. A Wind-up Toy has elastic potential energy in a compressed spring. When the spring unwinds the energy is converted to kinetic energy of the toy’s moving parts. Light bulbs convert electrical energy into thermal energy and electromagnetic energy.

4. Conservation of Energy The law of conservation of energy states that energy cannot be created or destroyed. The amount of energy present at the beginning of a process is the same as the amount of energy at the end. It may change forms of energy but the amount of energy will not change. Even friction changes kinetic energy into thermal energy. When the energy lost to frictional forces is accounted for, energy is conserved overall.

5. Friction Friction reduces the efficiency of machines. It is a major cause of energy consumption in cars and factories. All moving parts are subject to friction. Friction is everywhere. Even objects in free fall deal with the friction of air resistance. Most of an object’s potential energy is converted into thermal energy because of air resistance.

6. Energy Conversions The shift from potential energy to kinetic energy is one of the most common energy conversions. Gravitational potential energy of an object is converted into kinetic energy of motion as the object falls. How does a sea gull use energy conversion to open an oyster that can’t be opened with its beak? https://youtu.be/IqV5L66EP2E 4:38 https://youtu.be/IqV5L66EP2E

7. Pendulum Motion A pendulum consists of a weight swinging back and forth from a rope or string. The Dutch scientist Christian Huygens made the first pendulum clock in 1656. He made use of the fact that the time it takes for a pendulum to swing back and forth once is precisely related to its length. Potential energy and Kinetic energy undergo constant conversion as a pendulum swings.

9. Energy Conversion in Pendulums At the highest point in its swing, the pendulum is momentarily motionless as it changes direction. At this point, the weight at the end of the pendulum has zero kinetic energy and maximum potential energy. As it swings downward potential energy converts to kinetic energy. At the bottom of the swing, the pendulum has maximum kinetic energy and zero potential energy. https://youtu.be/51RCyBr_nGk 1:51 https://youtu.be/51RCyBr_nGk

11. Energy Conversion in the Pole Vault In the beginning, the athlete’s running provides kinetic energy. When he/she plants the pole at the base of the bars, the pole is bent as much as possible. At this point, it is at its maximum elastic potential energy. When the pole springs the athlete upward and over the bars, the elastic potential energy was converted to kinetic energy. When the athlete is at their highest position above the bars, for an instant, they are at their maximum gravitational potential energy that is quickly converted to kinetic energy as the athlete moves downward to a stop at ground level.

13. Energy Conversion Calculations Mechanical energy is the total kinetic and potential energy of an object. Therefore if friction is small enough to be ignored the following equation hold true. Mechanical energy = KE + PE Since the law of conservation states that energy cannot be created or destroyed in a closed system such as Earth, the mechanical energy at the beginning equals the mechanical energy at the end. (KE + PE) beginning = (KE+PE) end

14. Do the Math At a construction site, a 1.50 kg brick is dropped from rest and hits the ground at a speed of 26. meter per second. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it dropped. (PE) beginning = (KE) end Formula for KE ½ mv 2 PE = KE = ½ mv 2 PE = ½(1.50kg)(26.0 m/s 2 ) What will the answer be? Don’t forget the units!

15. Energy and Mass Einstein developed his special theory of relativity in 1905 which amounts to the equation E = mc 2. E equals energy. Lower case m equals mass. Lower case c is the speed of light. What this actually means is that energy and mass are equivalent and can be converted into each other. A tiny amount of matter in this case 1 gram can produce enormous amounts of energy. In this case, E = 1 gram (10 -3 kg) x (3x10 8 m/s) x (3x 10 8 m/s)= (10 -3 kg) x (9x10 16 m/s) = 9x10 13 kg*m 2 /s 2 = 9x10 13 J which is 90,000,000,000,000 Joules whereas one gram of TNT produces only 2931 J. The Law of Conservation is mass and energy together are always conserved. https://youtu.be/ql6TKCo2SZQ 3:29https://youtu.be/ql6TKCo2SZQ

16. Conclusion The Law of Conservation of energy states that energy cannot be created or destroyed. Energy may change from one form of energy to another and even friction does not destroy energy but converts it into thermal energy. The shift from potential energy to kinetic energy is the most common energy conversion. A pendulum and someone pole vaulting demonstrate how potential energy and kinetic energy continuing move from one to the other. Einstein’s E=mc 2 also demonstrates how matter and energy together are conserved.