Ch 5 Sect 1 The Nature of Energy

Chapter 5 Section 1 – What You’ll Learn Before you read - write the reading’s objectives in this space: 1 – _________________________________________________________________________________ 2 – _________________________________________________________________________________ 3 - __________________________________________________________________________________ 4 - __________________________________________________________________________________

Chapter 5 Section 1 – What You’ll Learn Before you read - write the reading’s objectives in this space: 1 – Distinguish between kinetic and potential energy. 2 – Calculate kinetic energy. 3 – Describe different forms of potential energy. 4 – calculate gravitational potential energy.

What is energy? __________________________________________ When something has the ability to change its environment Or change its self it has energy. 1

What is energy? The ability to cause change. When something has the ability to change its environment Or change its self it has energy. 1

You use energy to arrange your hair to look the way you want it to. You also use energy when you walk down the halls of your school between classes or eat your lunch. Change Requires Energy

Energy has several different forms, what are they? Describe each. __________________________________________ 2

Energy has several different forms, what are they? Describe each: Electrical – flow of electric charge through a conductor Chemical – energy in a substance that can be changed by chemical reaction. Radiant – transmitted by waves Thermal – caused by heat or temperature 2

If you have $100, you could store it in a variety of forms—cash in your wallet, a bank account, travelers’ checks, or gold or silver coins. It can be changed to other forms. An Energy Analogy You could deposit your cash into a bank account or trade the cash for gold. Regardless of its form, money is money. The same is true for energy. Energy from the Sun that warms you and energy from the food that you eat are only different forms of the same thing. 3

Define Kinetic energy (KE)? _________________________________________ What does KE depend on? _________________________________________ What is the formula? 4 What is the SI unit of energy?________ What is the abbreviation? ______ What is a Joule equal to? ___________

Define Kinetic energy (KE)? The energy a moving object What does KE depend on? The objects mass and speed What is the formula? 4 What is the SI unit of energy? joule What is the abbreviation? J What is a Joule equal to? kg*m 2 /s 2 Kinetic energy (J) = ½ X mass (kg) x velocity 2 (m 2 s 2 ) KE = (½ )(m)(v 2 ) (2)(KE) = v 2 (2)(KE) = m m v 2

What is the kinetic energy of a beach ball moving at 1.5m/s if the beach ball has a mass of 200g? 5

KE=½ mv 2 ( )( )( ) = kg 1.5 m kg m 2 2 s s J 5

A toy car is moving at a speed of 2m/s and has a KE of 0.24J. What is the car’s mass? 6

(2)(KE) = m v 2 (2) (0.24 J kg m 2 /s 2 ) = 0.12kg (2m/s)(2m/s) 6

A hanging apple in a tree has stored energy. What is stored energy due to position called? Even motionless objects can have energy. This energy is stored in the object. 7 _____________________________________________

A hanging apple in a tree has stored energy. What is stored energy due to position called? Even motionless objects can have energy. This energy is stored in the object. 7 Potential Energy (PE)

If the apple stays in the tree, it will keep the stored energy due to its height above the ground. Potential Energy (PE) If it falls, that stored energy of position is converted to energy of motion. Kinetic Energy (KE) 8

If you stretch a rubber band and let it go, it sails across the room. As it flies through the air, it has kinetic energy due to its motion. Where did this kinetic energy come from? ________________________________________ What is EPE?________________ _____________________________ ______________________________ 9

If you stretch a rubber band and let it go, it sails across the room. As it flies through the air, it has kinetic energy due to its motion. Where did this kinetic energy come from? Elastic Potential Energy What is EPE? Energy stored by something that can stretch or compress, such as a rubber band or spring. 9

What is Chemical Potential Energy? _________________________________________ 10

What is Chemical Potential Energy? Energy stored in chemical bonds 10

Energy is stored in the bonds that hold the carbon and hydrogen atoms together and is released when the gas is burned. In this chemical reaction, chemical potential energy is released.

Define Gravitational Potential Energy: _________________________________________ 11 What is the formula for GPE? On Earth the acceleration of gravity is 9.8 m/s 2, and has the symbol G. Like all forms of energy, gravitational potential energy is measured in joules.

Define Gravitational Potential Energy: Anything that can fall has stored energy called gravitational potential energy. (GPE) is energy stored by objects due to their position above Earth’s surface. 11 What is the formula for GPE? GPE = h GPE = G GPE = m mG mh Gh

According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground. Use MGH to find GPE of a ball at two different heights. First ball: Second ball: M= 0.30kg M=0.30kg G= 9.8m/s 2 G=9.8m/s 2 H=5m H=10m Changing GPE 12

According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground. Use MGH to find GPE of a ball at two different heights. First ball: Second ball: M= 0.30kg M=0.30kg G= 9.8m/s 2 G=9.8m/s 2 H=5m H=10m Changing GPE 12.3kg(9.8m/s 2 )(5m) = 14.7J.3kg(9.8m/s 2 )(10m) = 29.4J

Changing GPE If two objects are at the same height, then the object with the larger mass has more gravitational potential energy. Use MGH to find GPE of a ball at two different masses. First ball: Second ball: M= 0.30kg M=0.20kg G= 9.8m/s 2 G=9.8m/s 2 H=5m 13

Changing GPE If two objects are at the same height, then the object with the larger mass has more gravitational potential energy. Use MGH to find GPE of a ball at two different masses. First ball: Second ball: M= 0.30kg M=0.20kg G= 9.8m/s 2 G=9.8m/s 2 H=5m 13.3kg(9.8m/s 2 )(5m) = 14.7J.2kg(9.8m/s 2 )(5m) = 9.8J

What is the height of an object dropped if it has a mass of 1.2kg and a GPE of 176.4J? 14

What is the height of an object dropped if it has a mass of 1.2kg and a GPE of 176.4J? GPE = h mG J Kg m 2 /s 2 = 15m (1.2 kg) (9.8m/s 2 ) 14

An astronaut drops a tool from a height of 4m on the moon. The moon’s gravity is 1.67 m/s 2 and the GPE is 16.7J. What is the tool’s mass? What is that in pounds ? 15

An astronaut drops a tool from a height of 4m on the moon. The moon’s gravity is 1.67 m/s 2 and the GPE is 16.7J. What is the tool’s mass? What is that in pounds ? GPE = m Gh 16.7 J kg m 2 /s 2 = 2.5kg (1.67 m/s 2 ) (4 m) 2.5 kg lb 5.51 lb 1 1 kg ( )( )= 15

Section Check A. change B. heat C. motion D. work Energy is the ability to cause __________. 1 1 Question 1 16

Section Check The answer is A. Energy is the ability to cause change and has several different forms. 1 1 Answer 16

Section Check What are the four different forms of energy? 1 1 Question 2 17

Section Check What are the four different forms of energy? The four different forms of energy are electrical, chemical, radiant and thermal. Answer 1 1 Question 2 17

Section Check A. the object’s mass and speed B. the object’s mass C. the object’s speed D. the acceleration of the object The kinetic energy of an object depends on __________. 1 1 Question 3 18

Section Check The answer is A. Kinetic energy depends on both the mass and speed of the moving object. 1 1 Answer 18