 # Writing prompt – 10/13/06 IN COMPLETE SENTENCES: Write down the order of changes in energy that happens when plucking a guitar string. (longest chain of.

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Writing prompt – 10/13/06 IN COMPLETE SENTENCES: Write down the order of changes in energy that happens when plucking a guitar string. (longest chain of energy transfers gets candy!!!!)

Energy and Work!!! They’re pretty much the same thing…

Energy Definition: The ability of some physical system to do work. The units of energy and work are Joules (J) Some different types we named  Potential Gravitational, Spring, Chemical, Nuclear,  Kinetic Motion, Heat, Sound (Vibration)

Mechanical Energy The big types we’ll focus on are KINETIC, GRAVITATIONAL POTENTIAL, and SPRING POTENTIAL ENERGY These can all be listed as types MECHANICAL ENERGY

Gravitational Potential Energy What changes how much potential energy you have?  Height  Mass So how can you increase something’s potential energy?  Increase the mass or the height

Gravitational Potential Energy How do we calculate Gravitational potential energy? This equation: PE = mgh m=mass, h=height, g=9.81 m/s 2 g is the acceleration of gravity, it’s CONSTANT

Gravitational Potential Energy PE = mgh So how much energy does a 5kg ball that is held at a height of 2 meters? PE= mgh = 5 X 2 X 9.81=98.1 J

Gravitational Potential Energy PE = mgh How about a 10kg ball at 1m high? PE= mgh = 10 X 1 X 9.81=98.1 J

Kinetic Energy What changes how much kinetic energy you have?  Velocity  Mass So how can you increase something’s potential energy?  Increase the mass or the velocity of it

Kinetic Energy How do we calculate Kinetic energy? This equation: KE = 1/2mv 2 m=mass, v=velocity NOTE: V squared does NOT equal V x 2!!! V squared = V x V

Practice with KE = ½ mv 2 How much kinetic energy does a runner of 40 kg running at a speed of 5 m/s have? KE = ½ mv 2 = ½ x 40 x 5 2 = ½ x 40 x 25 = 500 J

Kinetic Energy Practice with KE = ½ mv 2 If a ball has 200J of energy and a mass of 4kg what is its VELOCITY? KE = ½ mv 2 so… 200 = ½ x 4 x v 2 so v = square root(200/2)

Conservation of Energy Energy CANNOT be created or destroyed, it can only be CHANGED!!! So a ball held in the air has potential energy, what does it change into as it falls?  KINETIC!!!

Conservation of Energy If a ball has 10J of potential energy before it is dropped, how many joules of kinetic energy does it have at the bottom of its fall? 10 joules!!! – the potential just turned into the kinetic

Let’s see a demo 4 different “roller coaster hills” Which one is going faster at the bottom Let’s vote and try it out

So from the demo… All the potential turned into kinetic The speed at the bottom was the same regardless of how fast it got down there or the hill shape.

Let’s try it out Find energies of different objects and plot them on bar graphs.

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