CHAPTER 4 ENERGY SECTION 1 The Nature of

CHAPTER 4: ENERGY

SECTION 1: The Nature of Energy

WARM-UP: What is energy? List some different types of energy.

LEARNING GOALS Distinguish between kinetic and potential energy. Calculate kinetic and gravitational potential energy. Describe different forms of potential energy.

WHAT IS ENERGY? Changes are constantly occurring in the world. Examples: light bulbs heating the air, sunlight on window, you breathing

WHAT IS ENERGY? Every change requires energy. Energy: ability to cause change

FORMS OF ENERGY Electromagnetic energy: energy that travels in waves Example: UV, Infrared, Radio Mechanical energy: energy in physical movement or position Example: moving car, flying baseball

FORMS OF ENERGY Electrical energy: energy carried by moving electrons Example: any kind of electricity Thermal energy: energy related to temperature Example: cup of hot tea

UNITS OF ENERGY Joule (J) – SI unit of energy Other units: calorie (cal) Calorie (Cal) Kilowatt Hour (k. Wh)

KINETIC ENERGY Kinetic Energy: the energy that a moving object has because of its motion. Depends on the mass and speed of the object.

KINETIC ENERGY KE = ½ 2 mv KE = kinetic energy in joules (J) m = mass in kg v = velocity in m/s

KINETIC ENERGY 2 mv KE = ½ 2 m = 2(KE/v ) v = √ 2(KE/m)

EXAMPLE A jogger with the mass of 60 kg is moving at a speed of 3 m/s. What is the jogger’s kinetic energy?

EXAMPLE A sprinter has a mass of 80. 0 kg and a kinetic energy of 4, 000 J. What is the sprinter’s speed?

EXAMPLE A baseball is moving at a speed of 40 m/s and has 120 J of kinetic energy. What is the mass of the baseball?

POTENTIAL ENERGY Potential Energy: stored energy due to an object’s position. Three types: elastic chemical gravitational

POTENTIAL ENERGY Elastic Potential Energy: energy stored by something that can stretch or compress Ex: rubber bands, springs

POTENTIAL ENERGY Chemical Potential Energy: energy stored in chemical bonds Ex: gasoline, food, batteries

POTENTIAL ENERGY Gravitational Potential Energy: energy stored in objects due to their position above the Earth’s surface Ex: a boulder on a cliff

POTENTIAL ENERGY GPE = mgh GPE = gravitational potential energy (J) m = mass in kg g = 9. 8 m/s 2 h = height in m

POTENTIAL ENERGY GPE = mgh m = GPE/(gh) h = GPE/(mg) g = GPE/(mh)

EXAMPLE What is the gravitational potential energy of a ceiling fan that has a mass of 7 kg and is 4 m above the ground?

EXAMPLE How high above the ground is a baseball with a mass of 0. 15 kg and a GPE of 73. 5 J?

EXAMPLE A rock climber is 200 m above the ground and has a GPE of 117, 600 J. What is the rock climber’s mass?

CHANGING ENERGY If all of the object on the shelves have the same mass: Which has the most potential energy? Which will be moving faster if they were to all fall?

CHANGING ENERGY As an object begins to fall, it has both GPE and KE. As the object gets closer to the ground, it has less GPE and more KE.

EXAMPLE An 80 kg diver jumps from a 10 m platform. What is the GPE of the diver at the top of the platform? What is the GPE of the diver after falling 5 m?

CHECK-IN: Explain how the kinetic energy of a truck could be increased without increasing the truck’s speed.