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Gravitational Potential Energy and Elastic Potential Energy Slide 48 / 111 Gravitational Potential Energy

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Gravitational Potential Energy and Elastic Potential Energy Slide 48 / 111 Gravitational Potential Energy Slide 1 / 111 Slide 2 / 111 Energy of Objects in Motion www.njctl.org Slide 3 / 111 Energy of Objects in Motion Click on the topic to go to that section · Energy and its Forms · Mechanical Energy · Energy of Motion · Stored Energy · Conservation of Energy · Types of Energy Resources Slide 4 / 111 Review from Last Unit In the previous units we have been studying the motion of objects. We talked about how far and fast an object goes if a force is applied to it. Why does a force cause an object to accelerate? Answer Slide 5 / 111 Energy and its Forms Return to Table of Contents Slide 6 / 111 What is Energy? Energy is a measurement of an object's ability to do work. How would you define work? How would you know if any work was being done? Slide 7 / 111 What is Energy? Energy is a measurement of an object's ability to do work. Work is defined as applying a force in order to move an object in a given direction. The more work that is done by an object, the more energy it exerts. Since energy is equal to work, the unit for both is the same, the Joule (J). 1 Joule = 1 Newton-meter Slide 8 / 111 Work Work can only be done to a system by an external force; a force from something that is not a part of the system. So let's say our system is a plane and the gate assistance vehicle. When the vehicle comes along and pushes back the plane, it increases the energy of the plane. The assistance truck is essentially doing work on the plane. Slide 9 / 111 Work The amount of work done is the change in the amount of energy that the system will experience. This is given by the equation: W = E final - Einitial · When a force is applied which causes the object to speed up and move a distance, the work is _______________. · If a resistive force was applied which caused the object to slow down over a distance, or not move at all, the work would be ____________. (think about acceleration) Slide 10 / 111 Positive Work If the object moves in the same direction as the direction of the force, the energy of the system is increased. The work is positive: W > 0. They can push the truck to get it to move! Slide 11 / 111 Negative Work If the object moves in the direction opposite the direction of the force then the work is negative: W < 0. The energy of the system is reduced. Pushing on the wall as hard as they can won't ever move the wall! Slide 12 / 111 Mechanical vs. Non-Mechanical Energy Energy exists in many forms, but can be broken down into two major forms: Mechanical Energy - The Energy of an object due to its motion and position. Mechanical Energy is the sum of the Kinetic and Potential Energy of an object. Mechanical Energy is usually used to describe a large object. Non-Mechanical Energy - The Energy of an object that is not due to it's motion or position. Non-Mechanical Energy usually describes an object at it's atomic level. Slide 13 / 111 1 Which of the following is the unit for energy? A Meter B Newton C Second Answer D Joule Slide 14 / 111 2 A wagon is rolling down a hill, a man tries to stop the wagon by trying to push it back up the hill but he is unsuccessful. Is the man doing positive or negative work? A positive B negative Answer Slide 15 / 111 3 A boy kicks a soccer ball into a net. Did the boy do positive or negative work on the ball? A positive B negative Answer Slide 16 / 111 4 A woman walks across an icy sidewalk that has been covered in salt to help make it less slippery. Is the salt doing positive or negative work on the woman's shoes? A positive B negative Answer Slide 17 / 111 Mechanical Energy Return to Table of Contents Slide 18 / 111 Forms of Mechanical Energy Mechanical Energy can be broken down into two different types of Energy: Energy of Motion, which is called Kinetic Energy and Stored Energy, which is called Potential Energy. Potential Energy has two forms, Gravitational and Elastic, depending upon how the Energy is stored. __________ Energy Write the underlined words into the correct place in the diagram. __________ Energy __________ Energy Slide 19 / 111 5 Which of the following is a form of Mechanical Energy? A Kinetic B Thermal Answer C Chemical D Solar Slide 20 / 111 Energy of Motion Return to Table of Contents Slide 21 / 111 6 Which of the following is a type of energy which is used to describe the motion of an object? A Electrical Energy B Nuclear Energy Answer C Potential Energy D All of the above Slide 22 / 111 Energy of Motion In order for an object to move, one of two scenarios has to occur: The object uses some of the potential energy that it had stored. The object is being given energy from an outside source. In either case, now that the object is in motion, the object is experiencing Kinetic Energy. Slide 23 / 111 Kinetic Energy An object's state of motion can be described by looking at the amount of kinetic energy that the object has at that moment in time. Since the state of motion of an object can change with time, the kinetic energy of an object can also change with time. Slide 24 / 111 Kinetic Energy The amount of Kinetic Energy that an object possesses is dependent on two factors: mass and velocity. Both of these factors are directly proportional to the kinetic energy. We talked about this mathematical relationship in the last chapter. What did directly proportional mean? Slide 25 / 111 Kinetic Energy, Mass, Velocity The larger the mass, the more energy is needed to move the object, therefore the _______________ the kinetic energy. Since kinetic energy is the energy of motion, the object has to have a velocity to have kinetic energy. The larger the velocity, the __________________ the kinetic energy. Slide 26 / 111 How Does Kinetic Energy Depend on Mass? If two identical objects are moving at the same velocity then they will have the same kinetic energy. v = 5 m/s If however, one object has more mass than the other while traveling at the same velocity, the heavier object will have more kinetic energy. v = 5 m/s A tennis ball and a bowling ball are both shown above. The bowling ball is heavier than the tennis ball. If they were both to move at the same velocity, which ball would have more kinetic energy? Slide 27 / 111 Velocity vs. Speed Remember that velocity is another way to measure motion. Simply put, velocity is the speed of an object with direction. Speed does not have a direction, so we call speed a scalar quantity. Since velocity has both magnitude and direction, it is a vector quantity. Runner's speed: 10 km/hr Runner's velocity: 10 km/hr to the East Slide 28 / 111 What is Kinetic Energy? In this picture, the hare is moving faster than the tortoise at this point. If we assumed that they had the same mass, who would have more kinetic energy? Why? Discuss this with a partner. Slide 29 / 111 How Does Kinetic Energy Depend upon Velocity? If two identical objects are moving at the same velocity then they will have the same kinetic energy. If however, one of the object's is moving faster, the one which is moving faster will have more kinetic energy. v = 5 m/s v = 10 m/s In the diagram above, two identical tennis balls are moving. Which tennis ball has more kinetic energy and why? Slide 30 / 111 7 Three different emergency vehicles are noticed driving on the highway at a speed of 25 m/s. Which of the following cars have the most kinetic energy at that moment? A a police car Answer B an ambulance C a Firetruck D they all have the same kinetic energy Slide 31 / 111 8 Three different baseball pitchers had the speed of their fastball measured by a radar gun. Which of the following pitcher's fastball had the smallest amount of kinetic energy? A a little league pitcher Answer B a high school pitcher C a major league pitcher D they all had the same kinetic energy Slide 32 / 111 9 Which of the following situations has the lowest kinetic energy? Be ready to explain your answer. A a man sitting on a park bench B a child riding a bike Answer C a woman driving a car D it is impossible to tell Slide 33 / 111 Calculating Kinetic Energy Kinetic Energy can be solved for by using the equation: 1 2 KE = 2 mv Fill in the table below. Name variable units Kinetic Energy m m/s Slide 34 / 111 Example - Calculating Kinetic Energy A car, which has a mass of 1,000 kg, is moving with a velocity of 5 m/s. How much Kinetic Energy does the car possess? 1 KE = 2 mv2 KE = (0.5)(1000 kg)(5 m/s)2 KE = (0.5)(1000 kg)(25 m2/s2) Teacher Notes KE = 125,000 J Slide 35 / 111 10 A 10 kg snowball is rolling down a hill. Just before reaching the bottom, it's velocity is measured to be 10 m/s. What is the Kinetic Energy of the ball at this position? Answer Slide 36 / 111 11 A 100 kg man running back in football is running with a velocity of 2 m/s.
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