What is energy???

1. What is energy??? • Usually, in most textbooks and online resources, you will see energy being described as “the ability to do work” • Sort of imprecise and is rather confusing if you don’t already have a firm understanding of what “work” actually is • Because of this, we will take a slightly different approach and define energy in the following manner: • Energy is a conserved, substance-like quantity with the capability to produce change in physical systems • James Joule’s research led to the idea behind “conservation of energy” • Led to development of 1st law of thermodynamics • Energy can be changed from one form to another, but it cannot be created or destroyed • Energy is measured in Joules (J) • 1 J = 1 N*m James Joule The total amount of initial energy, plus or minus any energy transferred into or out of a system, must equal the total final energy

2. Perpetual Motion Machines • Perpetual motion devices or “free energy” machines cannot exist • Though we usually say they are “impossible” what we really mean is that based on the our understanding of how the universe works and the laws that govern it, there can be no such device or substance that would have more final energy that initial energy without any energy transferred into the system • Therefore, these cannot exist due to the fact that the idea violates the 1st law of thermodynamics Even after all we have learned about energy and the 1st law of Thermo. has never failed once….proposals for such inoperable machines have become so common that the US Patent and Trademark Office has made an official policy of refusing to grant patents for perpetual motion machines without a working model "examples" of perpetual motion machines in action

3. A Firm Grasp on Conservation of Energy After a day goes by

4. After some investigation, turns out one was under the rug Again, careful investigation indicates that the window was open and, upon looking outside, the other 2 blocks are found

5. Apparently a friend came over, with his own blocks, and had left some at the house

6. So the mom disposes the extra blocks from the friend, closes the window, and does not let the friend in. Everything is going along alright until one time she counts and finds only 7 blocks!!! • However, there is a box in the room, a toy box in which the blocks are put away in • Mom goes to open the box, but the boy screams, “No! Don’t open my box!” • Being extremely curious, and somewhat ingenious, she develops a scheme! 16 oz 3 oz

7. Even after mom has figured out this new scheme for finding out how many blocks are in the toy box without looking in it, a problem has occurred. The boy is hiding the blocks in a bathtub full of dirty water!! The water is so dirty that she can’t see how many blocks are in there. This requires her to come up with yet another ingenious scheme. 6.25 in 6 in

8. So what’s the point of the analogy? Take away the first term in our equations and we are calculating more or less abstract things • 1.) when we are calculating the energy, sometimes some of it leaves the system and goes away, or sometimes some comes in • 2.) In order to verify the conservation of energy, we must be careful that we have not put any in or taken any out • 3.) Energy has a large of number of different storage modes (the toy box & the dirty water) and there is a formula for each one • Gravitational, kinetic, potential, heat, elastic, electrical, chemical, thermal, nuclear, mass energy • 4.) If we total up the formulas for each of these contributions, it will not change

9. Energy Storage • Energy stored in the arrangement of matter in a force field is potential energy • Gravitational Potential Energy • Elastic Potential Energy • Chemical potential energy

10. Energy Storage Energy stored in motion is called kinetic energy • Random kinetic energy of molecules (heat, sound) can rapidly spread out to more molecules and become untransferrable to other storage modes • Unrecoverable internal energy in a system is called dissipated energy (Ediss)—not “lost” energy • Friction is usually the culprit for dissipating the kinetic energy of matter • Once energy has been dissipated, it cannot be transferred back to useful energy storage mechanisms • 2nd law of thermodynamics