1. E NERGY

2. N ATURE OF E NERGY Energy is all around you. You hear energy as sound, you see energy as light, you can feel energy in wind. Living organisms need energy for growth and movement. You use energy when you hit a tennis ball, compress a spring, or lift a grocery bag. Energy is the ability to do work. When work is done, energy is ___________ from one form to another. This _________ can never be 100% efficient. transferred transfer

3. F ORMS OF ENERGY Energy appears in many forms. There are five main forms of Energy. Mechanical Heat Chemical Electromagnetic Nuclear

4. M ECHANICAL AND H EAT E NERGY Mechanical energy is the Energy of motion. Examples: Water in a waterfall Wind Moving vehicles Sound Blood traveling through your body Heat Energy is the internal motion of atoms. The faster the molecules move, the more heat energy is produced. Examples: Friction Changes in state of matter

5. C HEMICAL AND N UCLEAR E NERGY Chemical Energy is Energy that exists in the bonds that hold atoms together. When bonds are broken, chemical energy is released. Examples: Digesting food…bonds are broken to release energy for your body to store and use. Nuclear Energy is when the nucleus of an atom splits, nuclear energy is released. Nuclear energy is the most concentrated form of energy. Fission/fusion

6. E LECTROMAGNETIC E NERGY Electromagnetic Energy is the energy of moving electric charges. Examples: Power lines carry electricity Electric motors are driven by electromagnetic energy Light is this form of energy (X-rays, radio waves, laser light etc.)

7. 7 W ORK IS E XCHANGE OF E NERGY Energy is the capacity (ability) to do work Two main categories of energy Kinetic Energy: Energy of motion A moving baseball can do work. A falling anvil can do work Potential Energy: Stored capacity to do work Gravitational potential energy (perched on cliff) Mechanical potential energy (like in compressed spring) Chemical potential energy (stored in bonds) Nuclear potential energy (in nuclear bonds) Energy is measured in Joules (J) 1 Joule = 1 Nm

8. 8 C ONVERSION OF E NERGY Falling object converts gravitational potential energy into kinetic energy Friction converts kinetic energy into thermal (heat) energy makes things hot (rub your hands together) irretrievable energy Doing work on something changes that object’s energy by amount of work done, transferring energy from the agent doing the work.

9. Examples of Energy Transfer: 1. Bow and Arrow: ______ is required to pull the bowstring back, a transfer of energy from __________ to ______ (or ________) energy in the bow/bowstring. When the bowstring is released, the energy has been transferred into the arrow’s _______ (or _______ ) energy. 2. Car skidding to a stop: _______ energy is transferred into ________ energy ( _____ _____). Work the person storedpotential motionkinetic Kinetic thermal Heat loss

10. ___________ _______________ Gravitational Spring (elastic) Potential Energy (U) – stored energy of position…has the “potential” to do work….. 2 types:

11. Gravitational Potential Energy: The potential energy given to an object a height, h, above the “ground” must equal the work done to lift the object a height, h… h mass, m W = F d W = _____ So… U g = _____ (mg)h mgh

12. Elastic(spring) Potential Energy: The potential energy given to an object because of elasticity. Hooke’s Law states: the distance (Δx) a spring is stretched or compressed away from the resting position is directly proportional to the Force (F s ) applied on it

14. How is kinetic energy measured, then? A derivation.... Multiply both sides by “d”… If V i = 0, d = ?... Rearranging terms…. What is acceleration times time?... Since energy is the capacity to do work, 1/2mv 2 must be a measure of motion energy!

15. Law of Conservation of Energy: Energy can NOT be _______ or ________…. Only transferred from one form to another. If there are no external forces (such as friction) doing work on a system, then …. ….where i = initial and f = final If there is friction, then friction does work on the system (W f ), resulting in “heat loss”… createddestroyed

16. 16 H EAT : E NERGY L OST ? Heat is a form of energy really just randomized kinetic energy on micro scale lattice vibrations in solids, faster motions in liquids/gases Heat is a viable (and common) path for energy flow Product of friction, many chemical, electrical processes Hard to make heat energy do anything for you Kinetic energy of hammer can drive nail Potential energy in compressed spring can produce motion Heat is too disordered to extract useful work, generally notable exceptions: steam turbine found in most power plants Solar core : heat is important in enabling thermo-nuclear fusion

17. WORK-ENERGY Theorem Recall from your reading the work-energy principle (theorem) and the law of conservation of energy are basically the same thing. In a closed system energy is ALWAYS conserved therefore the work done has to equal the change in either potential or kinetic energy. Remember this is only true is there are no dissipative forces like, friction, involved.

18. Examples: (1) The Pendulum…. Demo: Swinging pendulum PE is maximum at the ____ of the swing. KE is maximum at the _______ of the swing Simulation from physicsclassroom.com top bottom

19. (2) All the ramps below are 5 m high. Find the speed of the block at ground level for each case IF there is NO friction. Find the speed of case 1 by recalling free fall (assume g = 10 m/s 2 ). Think about energy conservation for Case 2 and 3. The speed at the bottom depends ONLY on the _________ from which the block fell, NOT on the actual ________ taken. 10 height path

20. Simulation from physicsclassroom.com (3) What happens to the skier once he hits level ground with “unpacked snow”? Where does the energy go? He ______ because his kinetic energy is transferred to ______. (“W” in the simulation is the “Work of friction”) stops heat

21. (4) Which block gets to the bottom first, assuming no friction? A!! Since the velocity at the bottom must be the same, d/t must be the same… (5)A bead slides due to gravity along an upright, frictionless wire. It starts from rest at A. How fast is it traveling at B? ______ D? _____ E? ______ Maximum Speed at _____? Only ____ matters! 10 m/s C ! hh

22. (6) The Physics of Roller Coasters: Every roller coaster begins with a motor pulling the coaster up a very high lift hill, which gives the coaster a large _________________. The coaster then traverses the track simply under the influence of _______, converting its potential energy into ________, and then repeating this process numerous times. However, it can never reach that initial height of the lift hill again.. Why? __________! Even though friction makes the ride slow over time, the ride is still exciting towards the end, because the _______ of the twists and turns is _________! potential energy gravity kinetic friction radiusreduced

23. Example: The “Batman” ride at 6 Flags, St. Louis h = 25.6 m PE = 0 line (a) Assuming no friction and that the coaster essentially starts from rest at the top of the lift hill, calculate the speed at the bottom of the first drop. i f

24. 24 L OOP - THE -L OOP In the loop-the-loop (like in a roller coaster), the velocity at the top of the loop must be enough to keep the train on the track: v 2 /r > g Works out that train must start ½r higher than top of loop to stay on track, ignoring frictional losses ½r½r r