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Lesson Objectives Concepts of energy and forms of energy will be discussed in this lesson. These concepts are combined with the work-energy theorem to provide a convenient means of analyzing an object or system of objects moving between an initial and final state. In the end of the lesson, students will be able to discuss and recognize energy. TOC

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Prerequisites This Lesson does not require specific science's knowledge background. However basic understanding in several science's concepts like momentum, velocity, force, and velocity are strongly recommended. TOC

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Table of Content Home Home Lesson Objectives Lesson Objectives Prerequisite Prerequisite Concepts of Energy Energy Energy Works Works Summary & Practice Summary & Practice Forms of Energy Potential Definition Definition Gravitational Potential Energy Gravitational Potential Energy Elastic Potential Energy Elastic Potential Energy Summary & Practice Summary & Practice Kinetic Definition Definition Summary & Practice Summary & Practice Mechanical Definition Definition Summary & Practice Summary & Practice Evaluation Evaluation TOC

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Concepts of Energy What? Energy is ability to do work. Work is displacement of an object caused by force acts upon the object. Why? When you work on an object, you transfer energy (Force) to that object Whenever work is done, energy is transferred or transformed to another systems Illustration AB TOC Energy

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Concepts of Energy cont.. Works Work can be expressed by the following equation. where F is the force, d is the displacement and the angle (theta Θ) is the angle between the force and the displacement vector. Perhaps the most difficult aspect of the above equation is the angle "theta.” Please see the illustration beside. Displacement can be a distance but sometimes, it is not, to make it easy displacement is a horizontal distance between start and end position. the standard metric unit of works is the Joule (J). One Joule is equivalent to one Newton of force causing a displacement of one meter. In other words: 1 Joule = 1 Newton x 1 Meter = 1 kg x m 2 /s 2 W = F x d x Cos Θ CLICK TO PLAY F dΘ TOC F d Θ=0 o F d Θ=180 o F d Θ=90 o

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Concepts of Energy cont.. Summary Three key ingredients to work - force, displacement, and cause In work’s mathematic equation, the angle (theta Θ) is the angle between the force and the displacement vector. And displacement (d) is a horizontal distance between start and end position. Practice A 10-N frictional force slows a moving block to a stop after a displacement of 5.0 m to the right. done ? Only F frict does work. F grav and F norm do not do work since a vertical force cannot cause a horizontal displacement. W frict =(10 N) * (5 m) * cos (180 degrees) = -50 Joules TOC

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Forms of Energy The two examples above illustrate the two forms of potential energy to be discussed in this lesson - gravitational potential energy and elastic potential energy. gravitational potential energelastic potential energy. Potential Energy An object can store energy as the result of its position. For example, the heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its position. When assuming its usual position (i.e., when not drawn), there is no energy stored in the bow. Yet when its position is altered from its usual equilibrium position, the bow is able to store energy by virtue of its position. This stored energy of position is referred to as potential energy. Potential energy is the stored energy of position possessed by an object. TOC

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Potential Energy cont.. PE grav = m * g * h In the above equation, m represents the mass of the object, h represents the height of the object and g represents the acceleration of gravity (g=9.8 m/s/s on Earth). Gravitational Potential Energy Gravitational potential energy is the energy stored in an object as the result of its vertical position or height. The energy is stored as the result of the gravitational attraction of the Earth for the object. The gravitational potential energy of the massive ball of a demolition machine is dependent on two variables - the mass of the ball and the height to which it is raised. There is a direct relation between gravitational potential energy and the mass of an object. More massive objects have greater gravitational potential energy. There is also a direct relation between gravitational potential energy and the height of an object. The higher that an object is elevated, the greater the gravitational potential energy. These relationships are expressed by the following equation: TOC CLICK TO PLAY h m g

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Potential Energy cont.. If a spring is not stretched or compressed, then there is no elastic potential energy stored in it. The spring is said to be at its equilibrium position. The equilibrium position is the position that the spring naturally assumes when there is no force applied to it. In terms of potential energy, the equilibrium position could be called the zero-potential energy position. There is a special equation for springs which relates the amount of elastic potential energy to the amount of stretch (or compression) and the spring constant. Elastic Potential Energy Elastic potential energy is the energy stored in elastic materials as the result of stretching or compressing. Elastic potential energy can be stored in rubber bands, trampolines, springs, an arrow drawn into a bow, etc. The amount of elastic potential energy stored in such a device is related to the amount of stretch of the device - the more stretch, the more stored energy. Springs are a special instance of a device which can store elastic potential energy due to either compression or stretching. A force is required to compress a spring; the more compression there is, the more force which is required to compress it further. For certain springs, the amount of force is directly proportional to the amount of stretch or compression (x); the constant of proportionality is known as the spring constant (k). TOC CLICK TO PLAY x x k

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1.A teacher applies a force to a wall and becomes exhausted. This statement is a example of work (Y –N). 2.A book falls off a table and free falls to the ground. This statement is a example of work (Y –N). 3.A cart is loaded with a brick and pulled at constant speed along an inclined plane to the height of a seat- top. If the mass of the loaded cart is 3.0 kg and the height of the seat top is 0.45 meters, then what is the potential energy of the loaded cart at the height of the seat-top? Potential Energy cont.. SUMMARY To summarize, potential energy is the energy which is stored in an object due to its position relative to some zero position. An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height. An object possesses elastic potential energy if it is at a position on an elastic medium other than the equilibrium position. PRACTICE N. This is not an example of work. The wall is not displaced. A force must cause a displacement in order for work to be done. Y. This is an example of work. There is a force (gravity) which acts on the book which causes it to be displaced in a downward direction (i.e., "fall"). PE = m*g*h PE = (3 kg ) * (9.8 m/s/s) * (0.45 m) PE = 13.2 J TOC

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Forms of Energy KINETIC ENERGY Kinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another). To keep matters simple, we will focus upon translational kinetic energy. The amount of translational kinetic energy (from here on, the phrase kinetic energy will refer to translational kinetic energy) which an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object. The following equation is used to represent the kinetic energy (KE) of an object. TOC time :5 43210 CLICK TO PLAY 10 864 2 0 distance: V = Speed of object = distance/time = d/t (m/s) KE = ½ * m * v 2 = ½ * m * d 2 /t 2 V= 2 m/s s m d=10m

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Kinetic Energy cont.. Summary Kinetic energy is a scalar quantity; it does not have a direction. The standard metric unit of measurement for kinetic energy is the Joule Kinetic energy of an object is directly proportional to the square of its speed. For example; for a twofold increase in speed, the kinetic energy will increase by a factor of four. Practice Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s! If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? KE = 0.5*m*v 2 KE = (0.5) * (625 kg) * (18.3 m/s) 2 KE = 1.05 x10 5 Joules If the speed is doubled, then the KE is quadrupled. Thus, KE = 4 * (1.04653 x 10 5 J) = 4.19 x 10 5 Joules. or KE = 0.5*m*v 2 KE = 0.5*625 kg*(36.6 m/s) 2 KE = 4.19 x 10 5 Joules TOC

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Forms of Energy As discussed earlier, there are two forms of potential energy discussed in our course - gravitational potential energy and elastic potential energy. Given this fact, the previous equation can be rewritten: potential energy TME=(PEgav+PEspring)+KE Mechanical Energy The energy acquired by the objects upon which work is done is known as mechanical energy. Mechanical energy is the energy which is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position) or combination of these. The total amount of mechanical energy is merely the sum of the potential energy and the kinetic energy. This sum is simply referred to as the total mechanical energy :kinetic energy potential energy TME= PE + KE CLICK TO PLAY TME= PE TME= PE + KETME= KE TOC

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Mechanical Energy cont.. Summary Three key ingredients to work - force, displacement, and cause In work’s mathematic equation, the angle (theta Θ) is the angle between the force and the displacement vector. And displacement (d) is a horizontal distance between start and end position. Practice A 10-N frictional force slows a moving block to a stop after a displacement of 5.0 m to the right. done ? Only F frict does work. F grav and F norm do not do work since a vertical force cannot cause a horizontal displacement. W frict =(10 N) * (5 m) * cos (180 degrees) = -50 Joules TOC

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EVALUATION Now, You have learned basics concepts about energy. Energy forms are either potential or kinetic. Potential energy comes in forms that are stored. Mechanical energy. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position) or combination of these.kinetic energypotential energy To check your understanding about previous lesson. Lets begin the test ! Remember this test is scored. START Summary

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Evaluation 1.Please define three key elements of work: CHECK SCORE GO TO THE NEXT QUESTION

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Evaluation… cont 2.A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. This statement is a example of work. YES NO SCORE

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Feedback INCORRECT! Remember !!! There are three key ingredients to work - force, displacement, and cause Click to try again SCORE

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Feedback CORRECT! This is not an example of work. There is a force (the waiter pushes up on the tray) and there is a displacement (the tray is moved horizontally across the room). Yet the force does not cause the displacement. To cause a displacement, there must be a component of force in the direction of the displacement. GO TO THE NEXT QUESTION SCORE

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Evaluation… cont 3.A rocket accelerates through space. This statement is a example of work. YES NO SCORE

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Feedback INCORRECT! Remember !!! There are three key ingredients to work - force, displacement, and cause Click to try again SCORE

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Feedback CORRECT! This is an example of work. There is a force (the expelled gases push on the rocket) which causes the rocket to be displaced through space. SCORE GO TO THE NEXT QUESTION

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Evaluation… cont 4.Missy Diwater, the former platform diver for the Ringling Brother's Circus, had a kinetic energy of 12 000 J just prior to hitting the bucket of water. If Missy's mass is 40 kg, then what is her speed? m/s CHECK SCORE GO TO THE NEXT QUESTION

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Evaluation… cont 5.A 900-kg compact car moving at 60 mi/hr has approximately 320 000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 30 mi/hr. (HINT: use the kinetic energy equation as a "guide to thinking.") SCORE CHECK FINISH

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Please Wait SHOW FINAL RESULT

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TOC YOU HAVE CORECT ANSWERS FROM TOTAL 5 QUESTION ITEM You Need To Retake This Lesson Again OH NO....

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