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Energy Kinetic and potential

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Forms of Energy Mechanical - energy with which moving objects perform work Ex: bicycle, sound Mechanical - energy with which moving objects perform work Ex: bicycle, sound Chemical - energy stored in substances because of their chemical makeup Ex: coal, oil, gasoline, foods Chemical - energy stored in substances because of their chemical makeup Ex: coal, oil, gasoline, foods Nuclear Energy - stored in the nucleus of the atom Ex: splitting or fusing the atom Nuclear Energy - stored in the nucleus of the atom Ex: splitting or fusing the atom Heat Energy - energy produced by molecular motion Ex: All molecules vibrate Heat Energy - energy produced by molecular motion Ex: All molecules vibrate

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Forms of Energy Electrical - energy as a flow of electrons through a conductor, such as a wire Ex: computers, television, appliances Electrical - energy as a flow of electrons through a conductor, such as a wire Ex: computers, television, appliances Light (Electromagnetic) - form of radiant energy that moves in waves Ex: solar panels Light (Electromagnetic) - form of radiant energy that moves in waves Ex: solar panels Conservation of Matter and Energy - energy and matter cannot be created or destroyed, only transformed Conservation of Matter and Energy - energy and matter cannot be created or destroyed, only transformed

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Work Work - a form of mechanical energy always measured in Joules (J) Work - a form of mechanical energy always measured in Joules (J) Work Formula Work Formula Work = Force x distance Work = Force x distance W = F x d W = F x d Units Joules Newtons meters Units Joules Newtons meters

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Power Power - the amount of work completed in an specific amount of time, units are Watts Power - the amount of work completed in an specific amount of time, units are Watts Power Formula Power Formula Power = Work / time Power = Work / time P = W / t P = W / t Units Watts = Joules / second ***See sample problems

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Daily Quiz #2 Sm 2 1. What type of energy refers to the movement of an object? 1. What type of energy refers to the movement of an object? 2. Which type of energy is often referred to as stored energy? 2. Which type of energy is often referred to as stored energy? 3. Which type of energy is calculated by multiplying the force of an object by the distance it moved? 3. Which type of energy is calculated by multiplying the force of an object by the distance it moved? 4. What are the units for energy? 4. What are the units for energy? 5. What are the units for power? 5. What are the units for power? 6. Power is calculated by dividing Work by what? 6. Power is calculated by dividing Work by what? Bonus : Which burns more calories running or walking a mile? Bonus : Which burns more calories running or walking a mile?

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Machines A machine is a device to make work easier. A machine is a device to make work easier. Machines do this by changing the size or the direction of the applied force. Machines do this by changing the size or the direction of the applied force. The force that is applied to a machine is called the effort force, f E. The force that is applied to a machine is called the effort force, f E. The work done on a machine is called work input, W i The work done on a machine is called work input, W i

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Work must always be done on a machine if the machine is to do any work. Work must always be done on a machine if the machine is to do any work. The distance through which the machine moves is the effort distance, d E. The distance through which the machine moves is the effort distance, d E. W i = F E X d E W i = F E X d E The force applied by the machine is called the resistance force, F R. The force applied by the machine is called the resistance force, F R. The resistance force is often the weight of the object being moved. It opposes the effort force. The resistance force is often the weight of the object being moved. It opposes the effort force.

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The distance the object moves is the resistance distance, d R. The distance the object moves is the resistance distance, d R. Machines can only multiply force. Because machines cannot multiply work, work output can never be greater than work input. Machines can only multiply force. Because machines cannot multiply work, work output can never be greater than work input. Mechanical Advantage is the number of times a machine multiplies the effort force. Mechanical Advantage is the number of times a machine multiplies the effort force. Efficiency is the comparison of the work output to work input. It is usually expressed as a percent. Efficiency is the comparison of the work output to work input. It is usually expressed as a percent.

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Efficiency = W O X 100 Efficiency = W O X 100 W I W I Ex) What is the efficiency of a machine that Has a work output of 200 J and a work input of 100 J? Efficiency = 200 J X 100 = 200 % 100 J 100 J High efficiency means that much of the work is changed to useful work output. The less friction in a machine the higher the efficiency.

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Energy can be classified as potential or kinetic Potential energy: energy of position Potential energy: energy of position The boulder has more gravitational potential energy when measured from point A compared to B. PE = mgh

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PE = mgh m = mass in kilograms m = mass in kilograms g = acceleration due to gravity g = acceleration due to gravity (9.8 m/s 2 ) (9.8 m/s 2 ) h = height in meters h = height in meters Potential Energy is measured in Potential Energy is measured in kg m/s 2 m = kg m/s 2 m = newton meter = Joules

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Example 1: If the boulder has a mass of 8kg, and distance B is 10m, what is the potential energy of the boulder relative to the plateau? If the boulder has a mass of 8kg, and distance B is 10m, what is the potential energy of the boulder relative to the plateau? 8kg 10m

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Answer: PE = mgh PE = mgh = 8kg 9.8m/s 2 10m = 8kg 9.8m/s 2 10m =784 J =784 J 8kg 10m

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Example 2: If distance A is 20m, what is the potential energy of the boulder relative to the bottom? If distance A is 20m, what is the potential energy of the boulder relative to the bottom? 8kg 20m

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Answer: PE = mgh PE = mgh = 8kg 9.8m/s 2 20m = 8kg 9.8m/s 2 20m = 1568 J = 1568 J 8kg 20m

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Example 3 When work is done to stretch something, it is called elastic potential energy. When work is done to stretch something, it is called elastic potential energy. Find the elastic potential energy stored in a drawn bow if it takes an average force of 100N to pull the arrow back a distance of 0.5 meters.

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Answer: PE = mgh = Fd PE = mgh = Fd Fxd = 100N x 0.5m = 50J

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Kinetic energy Energy of motion Energy of motion KE = ½ mv 2 KE = ½ mv 2

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KE = 1/2mv 2 m = mass in kilograms m = mass in kilograms v = velocity in meters/sec v = velocity in meters/sec Kinetic energy is measured in Kinetic energy is measured in kg m/s m/s = kg m/s m/s = kg m/s 2 m = kg m/s 2 m = newton meter = newton meter = Joules Joules

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Example 4 The bird has a mass of 2 kg. It is flying at a speed of 5 m/s. Find its kinetic energy. K KE = ½ mv2 = = ½ 2kg (5m/s)2 = = ½ 2kg 25 m2/s2 = = 25 joules

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Kinetic and potential energy conversions Describe the energy conversions in this picture: Describe the energy conversions in this picture: At the top: At the top: ¼ of the way down: ¼ of the way down: ½ way down: ½ way down: ¾ down ¾ down At the bottom: At the bottom: Is the sum of KE + PE a constant? Is the sum of KE + PE a constant? All PE, no KE 3/4 PE, 1/4 KE 1/2 PE, 1/2 KE 1/4 PE, 3/4 KE No PE, All KE Yes! It’s always 10,000 J in this case.

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Where are PE and KE maximums in this picture?

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What happens when the cord is cut? Potential energy is converted to kinetic energy!

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Kinetic and potential energy convert to one another KE max no PE PE max no KE PE max no KE

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How is mass related to energy? Albert gave us the answer! Albert gave us the answer! E=mc 2

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E=mc 2 E = energy in joules E = energy in joules m = mass in kilograms m = mass in kilograms c = speed of light c = speed of light (3 x 10 8 m/s) (3 x 10 8 m/s)

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A small mass gives a great amount of energy

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Nuclear energy- clean power for the world?

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Example: How much energy can be given off by 5 grams of mass? ( 10 paper clips = 5 g) How much energy can be given off by 5 grams of mass? ( 10 paper clips = 5 g) 5g = 0.005 kg 5g = 0.005 kg E=mc 2 E=mc 2 = 0.005kg x (3 x 10 8 m/s) 2 = 0.005kg x (3 x 10 8 m/s) 2 = 0.005 kg x 9 x 10 16 m 2 /s 2 = 0.005 kg x 9 x 10 16 m 2 /s 2 = 0.045 x 10 16 = 0.045 x 10 16 = 450,000,000,000,000 J = 450,000,000,000,000 J

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WOW!!! 450,000,000,000,000 J is the amount of energy in 3 million gallons of gasoline! 450,000,000,000,000 J is the amount of energy in 3 million gallons of gasoline!

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