Slide 1 / 122 Slide 2 / 122 8th Grade Energy of Objects of Motion 2015-10-28 www.njctl.org Slide 3 / 122 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 / 122 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? Slide 4 (Answer) / 122 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 By applying a force onto an object, energy to it. is given to the object. This energy is Answer added to the amount of energy the object Why does a force cause an object to accelerate? already possessed. If a resistive force is applied onto an object, then the force is taking energy away from the object causing it to decelerate. [This object is a pull tab] Slide 5 / 122 Energy and its Forms Return to Table of Contents
Slide 6 / 122 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 / 122 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. When work is done on an object by another object, there is a transfer of energy between objects. Since energy is equal to work, the unit for both is the same, the Joule (J). 1 Joule = 1 Newton-meter Slide 8 / 122 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. The gate assistance vehicle is not part of the system. When the vehicle comes along and pushes back the plane, it increases the energy of the plane. The assistance truck is an outside force doing work on the plane.
Slide 9 / 122 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 - E initial Fill in the blanks with "positive" or "negative". HINT: Think about how these statements relate to acceleration. When a force is applied to an object that causes it to speed up and · move a distance, the work is _______________. When a resistive force is applied to an object that causes it to slow · down over a distance, or not move at all, the work would be ____________. Slide 10 / 122 Positive Work If an object moves in the same direction as the direction of the force applied to it, 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 / 122 Negative Work If an object moves in the direction opposite to the direction of the force applied to it, then the work is negative: W < 0. The energy of the system is reduced. The parachute moves downwards, while air resistance acts upwards on the parachute.
Slide 12 / 122 Zero Work If an object does not move even when there is a force applied to it, then no work is done on the object! W=0 J The people exert a force onto the wall, but the wall does not move! Slide 13 / 122 Mechanical vs. Non-Mechanical Energy Energy exists in many forms, but can be broken down into two major forms: Non-Mechanical Energy Mechanical Energy - The The energy of an object energy of an object due to its that is not due to its motion and position. motion or position. Non- Mechanical energy is usually mechanical energy usually used to describe a large describes an object at its object. atomic level. Examples: It is the sum of kinetic and electrical energy potential energy. chemical energy thermal energy sound energy Slide 14 / 122 1 Which of the following is the unit for energy? A Meter B Newton C Second D Joule
Slide 14 (Answer) / 122 1 Which of the following is the unit for energy? A Meter B Newton Answer C Second D D Joule [This object is a pull tab] Slide 15 / 122 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 Slide 15 (Answer) / 122 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 Answer B B negative [This object is a pull tab]
Slide 16 / 122 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 Slide 16 (Answer) / 122 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 A [This object is a pull tab] Slide 17 / 122 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
Slide 17 (Answer) / 122 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 Answer B B negative [This object is a pull tab] Slide 18 / 122 5 Jill is waiting for the bus and she forgot her mittens. She rubs her hands together to keep them warm. In this situation, there is ______________ energy due to the movement of her hands. There is also _______________ energy due to the heat she generates by rubbing her hands together. A mechanical, non-mechanical B non-mechanical, mechanical Slide 18 (Answer) / 122 5 Jill is waiting for the bus and she forgot her mittens. She rubs her hands together to keep them warm. In this situation, there is ______________ energy due to the movement of her hands. There is also _______________ energy due to the heat she generates by rubbing her hands together. Answer A A mechanical, non-mechanical B non-mechanical, mechanical [This object is a pull tab]
Slide 19 / 122 Mechanical Energy Return to Table of Contents Slide 20 / 122 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. Write the __________ Energy underlined words into the correct place in the diagram. __________ Energy __________ Energy Slide 21 / 122 6 Which of the following is a form of mechanical energy? A Kinetic B Thermal C Chemical D Solar
Slide 21 (Answer) / 122 6 Which of the following is a form of mechanical energy? A Kinetic B Thermal Answer A - Kinetic C Chemical [This object is a pull D Solar tab] Slide 22 / 122 Energy of Motion Return to Table of Contents Slide 23 / 122 7 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 C Kinetic Energy D All of the above
Slide 23 (Answer) / 122 7 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 - Kinetic C Kinetic Energy [This object is a pull D All of the above tab] Slide 24 / 122 Energy of Motion In order for an object to move, one of two scenarios has to occur: 1. The object uses some of the potential energy that it had stored. 2. Energy is transferred to the object from an outside source. In either case, now that the object is in motion, the object is experiencing kinetic energy. Slide 25 / 122 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 26 / 122 Kinetic Energy The amount of kinetic energy that an object possesses is dependent on two factors: and velocity mass 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 27 / 122 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 28 / 122 How Does Kinetic Energy Depend on Mass? If two identical objects are moving at the same velocity, they will have the same kinetic energy. v = 5 m/s However, if one object has more mass than the other, 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. Which ball would have more kinetic energy?
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