HONORS

Law of Conservation of Energy Law of Conservation of Energy: energy can never be created or destroyed, it can only change forms. Because of this, it is important to understand all of the different forms energy can take. See if they can remember the ones we’ve learned so far! Kinetic (energy in motion) Potential (stored energy; can be Elastic, Chemical, or Gravitational) As I go through the next few slides I like to see if the students can guess the forms of energy from the picture.

Forms of Energy Radiant: light that comes from the sun and lightbulbs; used to see and as a power source. Also referred to as: solar energy or light energy. Thermal: heat that comes from fire, sun, etc.; used to heat objects

Forms of Energy Electrical: comes from outlets and power plants; used to power electrical devices. Sound: comes from a variety of sources; used most often for communication Nuclear: comes from releasing energy from the nucleus of an atom; used in nuclear power plants.

Forms of Energy Electromagnetic: form of energy that is reflected or emitted in the form of electrical and magnetic waves that can travel through space. Examples: Cell phone, radio, satellite, etc.

Chemical  light/thermal/sound Energy Transfers What are some examples of energy transfers/conversions? Chemical  light/thermal/sound Solar  Electrical Electrical Light

Electrical  electromagnetic Energy Transfers What are some examples of energy transfers/conversions? Photosynthesis Electrical  electromagnetic (and light and sound) Solar  Chemical Kinetic  Sound

We can use this idea to do some calculations. Energy Transfers Mechanical energy: the total amount of kinetic and potential energy in a system. In a falling object, GPE converts to KE as the object falls. Mechanical energy remains constant in this system, due to the Law of Conservation of Energy We can use this idea to do some calculations.

Example #1 Thomas is playing baseball with Matt. Thomas hits the 0.14 kg baseball and it moves with a velocity of 50 m/s. Assuming all energy is conserved, what is the height the ball could reach if hit straight upwards? What can we find with mass and velocity? Start by finding KE of the ball. If all energy is conserved, that means no energy is “lost”, so KE will eventually equal GPE at the peak of the ball’s height. What does this mean we can do? Substitute KE for GPE. Then we can rearrange and solve for height. I like to talk through this with students to see if they can process through it on their own before I lead them through solving it. It may even help to have them talk you through drawing a picture of this on the board.

Example #1 h = 127.6 m h = ? m = 0.14 kg v = 50 m/s a = 9.8 m/s2 Thomas is playing baseball with Matt. Thomas hits the 0.14 kg baseball and it moves with a velocity of 50 m/s. Assuming all energy is conserved, what is the height the ball could reach if hit straight upwards? h = ? m = 0.14 kg v = 50 m/s a = 9.8 m/s2 KE = ½ (.14)(50)2 KE = (.07)(2,500) KE = 175 J Therefore… GPE = 175 J (since all energy is conserved) GPE = ham h = 175 (9.8)(.14) 1.372 h = 127.6 m am am h = GPE am KE = ½ mv2