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ENERGY, WORK and POWER

ENERGY, WORK and POWER. How can we measure it? How does energy change when an object is in motion or changes position?. The ability to do work. “Stored” energy due to position or shape. Energy of motion. Potential. Kinetic. Gravitational PE = m x g x h. Joules (J).

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ENERGY, WORK and POWER

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  1. ENERGY, WORK and POWER How can we measure it? How does energy change when an object is in motion or changes position?

  2. The ability to do work “Stored” energy due to position or shape Energy of motion

  3. Potential Kinetic Gravitational PE = m x g x h Joules (J) mass x gravity x height Pull of gravity is 9.8 m/s2 KE = ½ m x v2 (mass x gravity) = weight Jumper at top of ski jump (gravitational PE) Speed skater racing around the track Molecules of sugar in a granola bar (chemical PE) Slalom skier on the downhill Curling stone gliding across the ice Stretched rubber band (elastic PE)

  4. Definition: Work is the product of _________________ and ________________. Work requires: __________________________ (no work is being done without it!) For a force to do work, it must act in the _____________________ direction as the motion of the object. Work = ____________________________ x ______________________________ Work is measured in: _________________________ We abbreviate it: _______ distance force motion same force distance Joules J James Prescott Joule

  5. Definition: Power is_______________________________________ In other words, __________________________________________ You can increase power by doing two things: 1. _____________________________________________________ 2. _____________________________________________________ Power = _____________________ ÷ ________________________ Power is measured in: _______________We abbreviate it: _______ the rate of doing work how quickly you apply force and move something MORE work done in a specific amount of time Do a specific amount of work in LESS time work time Watts W James Watt

  6. Calculating KE and PE How can we know how much energy is in an object?

  7. First, an easy one… • How can we compare the relative kinetic energy (in words) of a downhill skier moving at different speeds? • Rank them from most KE to least KE. Skier moving at 10 mph ____________________ Skier moving at 30 mph ____________________ Skier moving at 60 mph ____________________ Least KE medium KE most KE

  8. Calculating KE • Kinetic energy is the energy associated with objects that are MOVING. • We can calculate how much KE an object has by using the following formula: • KE = ½ mv2 • m = mass • v = velocity • make sure to follow order of operations!!! • Please Excuse My Dear Aunt Sally

  9. Calculating KE • For each problem you are trying to solve, it helps to organize and always follow a set of steps. This way, you can receive partial credit (possibly) for the work that is shown. First: write the formula Then: plug in the numbers Finally: write the answer (with units!!!)

  10. Examples of KE Meters per second Two bobsledders and their sleigh are travelling at 36 m/s south and have a mass of 390 kg. Calculate the kinetic energy of the sledders and their sleigh. write the formula plug in the numbers write the answer (with units!!!) KE = ½ mv2 KE = ½ x 390kg x (36m/s)2 252,720 J

  11. Examples of KE Determine the kinetic energy of a 100 kg winger skating toward the goal in a hockey game at a speed of 3.5 m/s. write the formula plug in the numbers write the answer (with units!!!) KE = ½ mv2 KE = ½ x 100kg x (3.5m/s)2 612.5 J

  12. Potential Energy • There are three types of potential energy: • elastic potential energy (what a rubber band has when it’s stretched out). • gravitational potential energy based upon the height of the object from Earth. • chemical potential energy (the energy stored in the bonds between atoms, like in sugar.)

  13. Calculating GPE • We can calculate how much gravitational PE an object has by using the following formula: • GPE = mg x h • m = mass • g = the acceleration due to gravity (always 9.8m/s2) • h = height • make sure to follow order of operations!!! • Please Excuse My Dear Aunt Sally

  14. Calculating GPE • If you are given a mass (the units will be kilograms), then you will need to multiply this mass by 9.8 m/s2 (the acceleration due to gravity) and also multiply by the height above the ground.

  15. Examples of PE A 100 kg skier jumper is at the top of a ramp 50 meters off the ground. What is the gravitational potential energy of the snowboarder? write the formula plug in the numbers write the answer (with units!!!) GPE = mg x h GPE = 100kg x 9.8m/s2 x 50m 49,000 J

  16. Examples of PE What is the gravitational potential energy of a 45 kilogram snowboarder who does tricks 5 meters above the surface of the halfpipe? write the formula plug in the numbers write the answer (with units!!!) GPE = mg x h GPE = 45kg x 9.8m/s2 x 5m 2205 J

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