This color = read and write down Ch. 5: Energizing With Energy This color = read and write down Any other color = read and think about

Every change that occurs, large or small, involves … energy! The Nature of Energy 1 What is energy? Wherever you are sitting as you read this, changes are taking place—lightbulbs are heating the air around them, the wind might be rustling leaves, rain changing to snow, your body turning food into heat (and the brown stuff)…and on…and on…. Every change that occurs, large or small, involves … energy!

Change Requires Energy The Nature of Energy 1 Change Requires Energy Energy - the ability to cause change OR the ability to do work. Measured in Joules (J) Anything that can cause a change must have energy. Think about all the things you can affect and change in a day’s time (for good and for bad). If you don’t have energy, you don’t feel like doing much of anything soooo… we NEED energy.

Energy has different forms The Nature of Energy 1 Energy has different forms Electrical energy– due to the flow of _________. Chemical energy – stored in chemical bonds (ex. food, gas, fuel) Radiant energy – radio waves, light, x-rays Thermal energy – heat Kinetic energy– movement Is the chemical energy stored in food the same as the energy that comes from the Sun or the energy stored in gasoline?

Radiant energy from the Sun travels a vast distance through space to Earth 1 It warms the planet and is the ultimate source of energy for every living thing on Earth. WHAT AM I ?

Things that are moving have it. Kinetic Energy – energy of movement measured in Joules (“Jewels”) Things that are moving have it. Things that are sitting still don’t. KE = ½ mv2 m is mass (kg) v is velocity (m/s) KE is kinetic energy in Joules (J)

Sample Problem: As a paralegal your boss (a lawyer) asks you to find the KE of a 1000 kg car that was going 20 m/s when it ran a red light and hit someone. Formula: KE = ½ mv2 Work: KE = ½ (1000 kg) (20 m/s)2 Answer: KE = 200,000 J

Potential Energy (P.E.)– stored energy. a) Elastic P.E. – from something that can stretch or compress. i.e. – rubber band, spring, shocks, tramp. b) Chemical P.E. – from chemical bonds i.e. – gasoline, food, bombs, natural gas c) Gravitational P.E. – anything that can fall i.e. – book on a bookshelf, roller coaster at the top of a hill (formula on next slide)

GPE = mgh GPE is gravitational potential energy (J) m is mass (kg) g is accel. due to gravity (9.8 m/s2) h is height (m) The higher off the ground something is the ______ potential energy it has!

Sample Problem: As an engineer’s assistant you need to find the GPE of a roller coaster part so you can order the right one. The mass is 1000 kg and it is 10 m off the ground at its highest point. Formula: GPE = mgh Work: GPE = (1000 kg)(9.8 m/s2)(10 m) Answer: GPE = (98,000 J)

Money can be used as an analogy for energy. 1 An Energy Analogy Money can be used as an analogy for energy. You have a $ 750,000 inheritance coming to you $ 400 is cash $17,500 is gold coins $ 130,000 is CD’s $ 40,000 is in a savings account $ 535,000 is in BASEBALL CARDS Would you want the baseball cards?

Regardless of its form, money is money. The same is true for energy. Energy from the Sun that warms you... Energy from the food that you eat… Energy from the powerplant that runs your play-station… are only different forms of the same thing.

Energy can change from one form into another but the total amount NEVER changes. Law of Conservation of Energy – energy CAN NEVER be created or destroyed.

Kinetic Energy 1 The SI unit of energy is the joule – symbol J. The Nature of Energy 1 Kinetic Energy The SI unit of energy is the joule – symbol J. If you dropped a softball from a height of about 0.5m, it would have a KE of about one joule before it hits the floor.

Example 3 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? ANS: KE = ½ mv2 KE = ½ (0.15 kg)(40 m/s)2 KE = 120 J

GPE: stored energy that is due to an object’s position. The Nature of Energy 1 GPE: stored energy that is due to an object’s position. If the apple stays in the tree, it will keep the stored energy due to its height above the ground.

The Nature of Energy 1 Potential Energy If it falls, that stored energy of its position is converted to energy of motion which is ______ ________.

8. Energy Transformations The Nature of Energy 1 8. Energy Transformations GPE  Kinetic and Electrical the dam Electrical  Radiant Cell phone Electrical  Kinetic (sound wave) mp3 player Chemical  Kinetic and Thermal - car taking off

Starting with the food I ate, diagram the energy transformations as I walk over and turn on the light. T.E. C.P.E K.E. E.E. Starting with the coal from the power plant, diagram the energy transformations on the hair dryer T.E. C.P.E. K.E. E.E. T.E.

Chemical Potential Energy The Nature of Energy 1 Chemical Potential Energy When natural gas is burned, energy stored in the bonds that hold the atoms together and is released .

9. Changing GPE 1 GPE changes with height above the ground. The Nature of Energy 1 9. Changing GPE GPE changes with height above the ground. The higher off the ground an object is, the more GPE it has. If two objects are at the same height, the one with the most mass has the most GPE.

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

Energy is the ability to cause ___change____. Section Check 1 Answer The answer is A. Energy is the ability to cause ___change____.

List four different forms of energy: Q. 2 Section Check 1 List four different forms of energy: Q. 2 Answer electrical, chemical, radiant and thermal, (potential & kinetic), GPE

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

Section Check 1 Answer The answer is A. Kinetic energy depends on __the object’s mass and velocity___.

minor rule changes If you are sent out to the hall to work on an assignment you must not disrupt other classes. If you do = automatic write-up No headphones during reading / notes / grading. Only while working on homework and some labs.

Transforming Electrical Energy Conservation of Energy 2 Transforming Electrical Energy Lightbulbs transform ________ energy into ______ and _______ energy.

Transforming Chemical Energy Conservation of Energy 2 Transforming Chemical Energy In a car, a spark plug fires, changing _______ potential energy into __________ energy.

Transforming Chemical Energy Conservation of Energy 2 Transforming Chemical Energy Then, as the hot gases expand, thermal energy is converted into ________ energy.

Transforming Chemical Energy Conservation of Energy 2 Transforming Chemical Energy Some energy transformations are less obvious because they do not result in motion, sound, heat, or light. Every green plant converts light energy from the Sun into chemical energy.

Conversions Between Kinetic and Potential Energy Conservation of Energy 2 Conversions Between Kinetic and Potential Energy 10. Mechanical energy (M.E.) – total amount of potential and kinetic energy in a system ME = PE + KE mechanical energy = potential energy + kinetic energy

2

2 Projectiles: the K.E. and P.E. change, but the M.E of the ball does ___ ________.

Energy Transformations in a Swing Conservation of Energy 2 Energy Transformations in a Swing 11. Pendulum – how is K.E. effected? more mass = _______ K.E. Shorter string = _____ K.E. Answer this question out loud “how is the energy conserved?”

Energy Transformations in a Swing Conservation of Energy 2 Energy Transformations in a Swing At the ends of the path you have max _____. As it accelerates downward, the P.E. changes over to ______. At the bottom of the path, KE is at its ______.

Be sure study guide packet is done Read through notes / powerpoints TEST TUESDAY Be sure study guide packet is done Read through notes / powerpoints 12. E.P.E – slingshots, rubber bands, etc. The ______ ball has more G.P.E The ______ ball has more E.P.E

13. What law is represented in the diagram? WRITE THE ANSWER The Law of Conservation of Energy 2 13. What law is represented in the diagram? WRITE THE ANSWER

Is energy always conserved? Conservation of Energy 2 Is energy always conserved? While coasting along a flat road on a bicycle you will eventually stop if you don’t pedal. A. Write an answer to this question: If energy is conserved, why don’t you keep coasting forever?

Converting Mass into Energy Conservation of Energy 2 Converting Mass into Energy 14. Nuclear Fusion—takes place in the Sun and other stars. Fusion - a small amount of mass is turned into a huge amount of energy.

Conservation of Energy 2 Nuclear Fission A. The energy before the reaction is equal to the energy after the reaction.

Conservation of Energy 2 15. Energy in Your Body Some of the chemical potential energy stored in your body is used to maintain a nearly constant internal temperature. A portion of C.P.E. is converted to heat that your body gives off.

Energy Conversions in Your Body Conservation of Energy 2 Energy Conversions in Your Body Your body stores C.P.E in the form of fat. It gets converted to: - T.E. (heat) K.E. (movement) This C.P.E. is used to fuel the processes that keep you alive (i.e. heart beat, breathing, and thinking).

Energy Conversions in Your Body Conservation of Energy 2 Energy Conversions in Your Body Walking burns the most calories for ______ body frame. _____ burns the most calories for all bodies

Every gram of fat a person consumes can supply 9 C of energy. Conservation of Energy 2 Food Energy Calorie (C) — measures food energy (C.P.E.) 1 C ≈ 4,184 J Carbohydrates and proteins each supply about 4 C of energy per gram. Every gram of fat a person consumes can supply 9 C of energy.

Q. 4 Mechanical energy is the total amount of _________ in a system. Section Check 2 Q. 4 Mechanical energy is the total amount of _________ in a system. A. kinetic energy B. momentum C. potential energy D. potential and kinetic energy

Section Check 2 Answer The answer is D. Mechanical energy is the energy due to position and motion of all objects in a system.

Q.5 Define the law of conservation of energy. Section Check 2 Q.5 Define the law of conservation of energy. Answer The law of conservation of energy states that energy cannot be created or destroyed. It can only change forms.

Q.6 Friction converts ________ energy into _________ energy. Section Check 2 Q.6 Friction converts ________ energy into _________ energy. A. electrical, thermal B. mechanical, thermal C. thermal, electrical D. thermal, mechanical

Section Check 2 Answer The answer is B. Friction converts mechanical energy into thermal energy.

Q. 7 KE = ½ mv2 Write what happens to the energy if the mass is doubled? Write what happens to the energy if the velocity is doubled? Why is this? Answer: If m is doubled, KE is doubled. If v is doubled, KE is quadrupled, because it is squared.

Einstein’s famous formula Reviewing Main Ideas 2 Einstein’s famous formula E = mc2 - E is energy, m is mass, and c is the speed of light. - States that mass is energy. - A tiny bit of mass gets converted to a huge amount of energy because the speed of light is a huge number.

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