Unit 9: Energy, Work, and Power Forms of Energy and Energy Transformations Indicators PS-6.1: Explain how the law of conservation of energy applies to the transformation of various forms of energy (including mechanical energy, electrical energy, chemical energy, light energy, sound energy, and thermal energy). PS-6.2: Explain the factors that determine potential and kinetic energy and the transformation of one to the other.

Objectives Differentiate between the different forms of energy: mechanical, electrical, chemical, light, sound, and thermal energy Use diagrams to explain energy transformations from one form to another. Use models to show transformations between PE and KE and conservation of total mechanical energy.

What is energy? Energy ◦ Ability or capacity to do work. ◦ Energy is never created or destroyed.  Law of Conservation of Energy ◦ Energy can be changed from one form to another ◦ Total amount of energy in a system is CONSTANT—it stays the same. How is energy being used by the man riding his bike?

What are the different forms of energy? Energy can be present in different forms of energy or a combination of forms. Mechanical ◦ Potential ◦ Kinetic ◦ Sum of potential + kinetic energy Chemical Electrical Thermal Light Sound

Mechanical Energy Mechanical energy is energy due to the position of something or the movement of something. Mechanical energy can be potential kinetic or the sum of the two. Potential energy (PE): stored energy Kinetic energy (KE): energy of motion How do these pictures show mechanical energy?

Potential Energy Potential energy is stored energy 3 types of PE ◦ Elastic Potential Energy  Stored energy when a material is stretched or compressed  Rubber Band ◦ Chemical Potential Energy  Energy stored in the bonds between atoms  Energy stored in food  Energy stored in batteries ◦ Gravitational Potential Energy  Stored energy due to position of an object  Height above the ground  Weight Lifting

Total Mechanical Energy PE can be converted to KE and back to PE Watch the animation and explain the transformation of energy. What is happening to TME?

Efficiency of Energy Transformations When PE is converted to KE, some of the energy is changed to heat/thermal energy due to friction. Energy transformations are NOT 100% efficient.

Check for Understanding The animation shows a dart being fired from a spring. A.What forms of energy are present? B.What happens to elastic potential energy PEs when the dart is fired? C.What happens to KE at first when the dart is fired? D.When does PEg increase? E.Explain why total mechanical energy TME does not change.

Chemical Energy Chemical energy is a type of energy that is associated with atoms, ions, and molecules and the chemical bonds that these particles form. When a chemical reaction happens, chemical energy is changed to another form. Examples ◦ Batteries store chemical energy ◦ Your body stores energy from food as chemical energy ◦ Photosynthesis  Plants use energy from the sun to make sugar. Energy is stored in the bonds of the sugar

Electrical Energy Electrical energy deals with the movement of electrons from an area of high potential to low potential

Other Forms of Energy Thermal ◦ Heat ◦ Associated with movement of particles ◦ Friction can cause KE to be converted to thermal energy Light ◦ Energy associated with electromagnetic waveselectromagnetic waves ◦ Light energy does NOT need a medium to travel ◦ Light can be transmitted through space  Sun gives us light energy  Sun is also a source of nuclear energy—nuclear fusion Sound ◦ Energy associated with mechanical longitudinal waves ◦ Sound needs a medium to travel ◦ It will not be transferred through space

Check for Understanding 1. Which of the following could be used to convert light energy to electrical energy? A. Windmill B. Chemical storage battery C. Solar Cell D. Rotating coils in a magnetic field 2. The stored energy in a battery can best be described as ____. A. Thermal B. Chemical C. Nuclear D. Kinetic

Check for Understanding 3. What kind of energy does a windmill use to do work? a. Electrical b. Nuclear c. Chemical d. Mechanical

TRANSFORMING ENERGY

Law of Conservation of Energy Energy cannot be created or destroyed. Energy can only be transformed or converted from one form to another form.

Examples of Energy Transformation Conservation of Energy in a Flashlight ◦ Step 1: Battery has chemical potential energy. ◦ Step 2: Chemical energy changes to electric energy. ◦ Step 3: Electric energy flows through the light bulb and turns electric energy to light and heat. The total of the energy from the chemical reaction (chemical PE in the battery) is equal to the total energy that it transforms into (electrical, light, and heat/thermal)

Examples of Energy Transformation Conservation of energy when baseball is thrown to another ball player. ◦ Step 1: A ballplayer converts chemical energy from the food she has eaten to mechanical energy when she moves her arm to throw the ball. ◦ Step 2: The work done on the ball converts the energy of the arm movement to kinetic mechanical energy of the moving ball. ◦ Step 3: When the second player catches the ball, the ball does work on the player’s hand and glove giving them some mechanical energy. The ball also moves the molecules in the glove heating them up. The player that catches the ball absorbs the energy of the ball and this energy turns to heat. The total heat produced is equal to the energy used to throw the ball.

Your Turn... Explain the energy transformations below.

POTENTIAL ENERGY AND KINETIC ENERGY

Gravitational Potential Energy Gravitational Potential Energy  GPE ◦ Energy of position ◦ Stored energy due to height ◦ GPE = mass x g x height Factors that affect GPE ◦ Weight (mass x g)  Large weight = greater GPE ◦ Height above a defined surface  An object at a greater height has more GPE

The boulder has more gravitational potential energy when measured from point A compared to B. PE = mgh

Kinetic Energy Energy of motion ◦ Greater when the speed is greater ◦ Greater when the mass is greater KE = ½ mv 2 This means KE = mass x velocity 2 2

Transformation of PE to KE At maximum height, the ball has ALL PE and no KE As the ball rolls down the hill, some PE is converted to KE At the bottom of the hill the ball has no PE and ALL KE When the unbalanced force of friction acts on the ball, the KE is converted to thermal energy. Total mechanical energy is conserved PE at the top of the hill = KE at the bottom of the hill

Kinetic and potential energy conversions Describe the energy conversions in this picture: At the top: ¼ of the way down: ½ way down: ¾ down At the bottom: Is the sum of KE + PE a constant? All PE, no KE 3/4 PE, 1/4 KE 1/2 PE, 1/2 KE 1/4 PE, 3/4 KE No PE, All KE Yes! It’s always 10,000 J in this case.

Energy Transformation in a Pendulum

Energy Transformations in a Pendulum When a pendulum swings it has mechanical energy. At the top of the swing all of its mechanical energy is potential energy that depends on its height and weight. The kinetic energy is greatest at the bottom of the swing because its speed is greatest. Potential energy is zero at the bottom of the swing because the height is zero. Between the top of the swing and the bottom of the swing it has both potential and kinetic energy because it has both height and movement. Eventually the pendulum will stop. It stops because of friction. The friction transforms the energy that was originally mechanical energy in the swinging pendulum into heat.

Where are PE and KE maximums in this picture?

Check for Understanding What factors affect GPE??? What factors affect KE??? If you are on a swing, where would your speed be the greatest? WHY?

APPLICATION QUESTIONS