Chapter 4 Energy

The Nature of Energy What is energy? Energy is the ability to do work. Energy is the ability to cause a change. Examples: –Baseball flying through the air, a rollercoaster, CD player, lights, etc. There are 5 major forms of energy: –Mechanical, Heat, Chemical, Electromagnetic, and Nuclear.

The Nature of Energy 1.Mechanical Energy: Energy associated with motion. Examples: –Water in a water fall, wind, automobiles, planes, walking, riding a bike, hitting a ball, sound, etc. 2. Heat Energy: The internal motion of particles of matter. The faster the particles move, the more heat energy is present. Heat energy often causes changes in the temperature and phase (solid, liquid, or gas) of any form of matter. Examples: –Rubbing hands together turns mechanical energy into heat energy.

The Nature of Energy 3. Chemical Energy: The energy that bonds atoms or ions together. When bonds are broken, atoms are rearranged, and new bonds are formed. During this process, stored chemical energy is released. Examples: –Rocket fuel being ignited changes chemical energy into heat energy, BBQ grills, throwing a ball (muscles: chemical energy is used in your body in order to throw the ball).

The Nature of Energy 4. Electromagnetic Energy: Moving electrical charges. Power lines carry electromagnetic energy into your home in the form of electricity. Examples: –Electric motors, light (each color = a different amount of energy), x-rays, radio waves, laser light, etc.

The Nature of Energy 5. Nuclear Energy: Energy released by the splitting of the nucleus of an atom; energy locked within the nucleus by the strong force. Nuclear energy is the most concentrated form of energy. When a nucleus splits, nuclear energy is released in the form of heat energy and light energy. Examples: –The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei.

The Nature of Energy The five forms of energy can be classified as either kinetic or potential energy. Kinetic Energy (KE): The energy a moving object has because of its motion. The faster an object moves, the more kinetic energy it has. COPY THIS SLIDE IN THE MARGIN OF THE HANDOUT

Kinetic energy depends on both the mass of the object and the speed at which the object is moving. Kinetic Energy = ½ × (mass) × (velocity) 2 KE = ½mv 2 According to this equation, an increase in either mass or velocity of an object will increase the kinetic energy of the object. Measured in Joules (J).

The Nature of Energy Example: A jogger whose mass is 60-kg is moving at a speed of 3-m/s. What is the jogger’s kinetic energy? KE = ½ mv 2 KE = ½ (60-kg)(3-m/s) 2 KE = 270-J

The Nature of Energy Example: What is the kinetic energy of a baseball moving at a speed of 40-m/s if the baseball has a mass of 0.15-kg? KE = ½ mv 2 KE = ½ (0.15-kg)(40-m/s) 2 KE = 120-J

The Nature of Energy Example: You Try it A car moving at a speed of 20-m/s has a kinetic energy of 300,000-Joules. What is the car’s mass? KE = ½ mv 2 300,000-J = ½ (m)(20-m/s) 2 Mass = 1500-kg

The Nature of Energy Example: A sprinter has a mass of 80-kg and a kinetic energy of 4000-Joules. What is the sprinter’s speed? KE = ½ mv J = ½ (80-kg)(v) 2 Velocity = 10-m/s

The Nature of Energy 2. Potential Energy (PE): Energy stored in an object due to its position. Example: –As you stretch a rubber band, energy is put into it. In its new position, the stretched rubber band contains potential energy.

Question? If you are standing on the edge of a 1-m high diving board, do you have any energy? Yes – Potential energy; due to your position above the water below.

1 2 3 Panther drill: Write the number and then state whether the picture shows potential or kinetic energy 4 5 P P K P K

Exit Ticket KE = ½ x M xV 2 3 m Choose one of the skate boarder # 1,2, or 3, and calculate the KE and GPE for him. Make sure to circle the one you choose and show your work GPE= mph

Exit Ticket KE = ½ x M xV 2 3 m Choose one of the skate boarder # 1,2, or 3, and calculate the KE and GPE for him. Make sure to circle the one you choose and show your work GPE= mph

Review What is potential Energy? Stored Energy What is kinetic energy? Moving energy What unit is energy measured in? Joules (J) If you increase mass or velocity of an object what happens to the KE? It increases How do you figure out KE? KE = ½ mv 2

The Nature of Energy Energy that is dependent on the height above the earth’s surface is called gravitational potential energy (GPE). Weight also determines the amount of GPE an object has. GPE = Weight × Height GPE = Mass × Gravity × Height GPE = mgh

The Nature of Energy GPE = Weight × Height GPE = Mass × Gravity × Height GPE = mgh W = m x a g

The Nature of Energy The greater the weight and height of an object, the greater the GPE. Measured in Joules (J). Gravity = 9.81-m/s 2 (on Earth)

How it works GPE= m x g x h 5 x 9.8 x 2 98 joules (j) 5 kg 9.8 m/s 2 2 m

The Nature of Energy Example: What is the GPE of a ceiling fan that has a mass of 7-kg and is 4-m above the ground? GPE = mgh GPE = (7-kg)(9.81-m/s 2 )(4-m) GPE = 274-Joules

The Nature of Energy Example: Find the GPE of a coffee mug with a mass of 0.3-kg on a 1-m high counter top. GPE = mgh GPE = (0.3-kg)(9.81-m/s 2 )(1-m) GPE = 2.94-Joules

The Nature of Energy Example: YOU TRY Find the GPE of a baseball with a mass of 0.15-kg that has been thrown to a height of 50 m. GPE = mgh GPE = (0.15-kg)(9.81-m/s 2 )(50m) GPE = 73.5-J

What if you need other info? What if you need to find mass or height? Switch the formula around! GPE = m x g x h Mass = Height = GPE gxh GPE mxg

The Nature of Energy Example: You Try This time switch the formula around to find mass What is the mass of a hiker 200-m above the ground if her GPE is 117,600-J? GPE = mgh 117,600-J = (m)(9.81-m/s 2 ) ( 200-m) Mass = 60-kg

The Nature of Energy Other types of Potential Energy: Elastic potential energy is the energy stored by something that can stretch or compress. –Examples: Rubber band or spring. Chemical potential energy is energy stored in chemical bonds. –Examples: Gasoline or food.

A-B Partners 1.Each partner will do a problem and either A or B 2.Then you will explain to your partner how you got your answer 3.Each partner will sign of on the others work. 4.WHEN YOU ARE TOLD TO TURN IT IN THE BASKET

Problems Partner B What is the GPE of a person standing at the top of a ladder with a height of 15 meters? The person has a mass of 80 kg. Partner A What is the GPE of a ball with a mass of 0.5 kg and a height of 10 meters above the ground?

Individual Practice On your OWN!!! Choose 2 of the 3 problems on the small sheets of paper I give you. Answer the question, show your work, and bring them to me so I can see them when you are done when you are done. You have 5-10 minutes to complete this activity QUIETLY

Exit Ticket KE = ½ x M xV 2 3 m Choose one of the skate boarder # 1,2, or 3, and calculate the KE and GPE for him. Make sure to circle the one you choose and show your work GPE= mph

Extra Examples Use this equation: GPE = m x 9.8 m/s 2 x h What is the GPE of a bowling ball with a mass of 1.5 kg and held 2 meters above the ground? What is the GPE of a car with a mass of 505 kg and a height of 40 meters above the ground? (It’s falling off of a cliff)

Monday

Panther Drill In your owns words describe how energy is changed from when you turn a key in the car to after get to where you are going. DO YOUR BEST DON’T SWEAT IT IF IT’S NOT PERFECT.

Conservation of Energy Energy is always conserved, it can never be destroyed, only changed from one type of energy to another. The changes in the forms of energy are called energy transformations. The most common energy conversion: changing of potential energy to kinetic energy

EXAMPLES Examples: –A lightbulb converts electrical energy to light and heat energy. –A gasoline engine converts chemical energy eventually into kinetic energy.

Potential energy to kinetic energy Example: Rollercoasters –At the top of the first hill, the car has a maximum amount of potential energy and almost zero potential energy. –As the car rolls down the first hill, its kinetic energy increases and the potential energy decreases. –What happens to the cars energy as it goes up the next hill?

Conservation of Energy Mechanical energy (ME): The total amount of potential and kinetic energy in a system ME = KE + PE The total ME of an object always remains constant, it never changes.

Conservation of Energy Example: Suppose a ball is released from a height of 2.00-meters above the ground. –What is the gravitational potential energy of the ball before it is released? –What is the kinetic energy of the ball before it is released? –What is the total mechanical energy of the ball before it is released? –What is the kinetic energy of the ball just before it hits the ground after it is released?

Conservation of Energy Law of Conservation of Energy: energy cannot be created or destroyed. On a large scale, this law means that the total amount of energy in the universe does not change. The same amount of energy that was here at the big bang (15mil+ yrs ago) is here now!!!!

Conservation of Energy Most famous use of Law Albert Einstein dealt with the concept that mass and energy were interchangable. E = mc 2

Einstein said that matter is another form of energy, or that mass and energy are two forms of the same thing and can be converted into each other. E = mc 2 Resulted in Nuclear Bomb that ended what war when the USA used it? WWII

Energy Transformations What happens when turn on the TV? Potential Electric to Electric to Light energy & Heat energy How about when you run track? Chemical Potential in your body turns to kenetic energy in muscles & heat energy (sweat)

1-5 about Energy conversions 1-2 Still need a lot of help 3 I am ok w/ it 4 I am good with it 5 Take the day of Mr P I will teach it!!!