What do you think of when you hear the word ENERGY? (make a list of words that makes you think of energy) Food Movement Doing things Working Sunlight

Where do they get the energy to go down the hill? Essential Question: Why is energy so important to us? Energy

EVERYDAY ENERGY? What types of energy do you encounter everyday? How does energy get from one place to another? It will either transform or transfer.

So what is ENERGY?!?! Energy is NOT matter and is actually very difficult to define... Textbooks define it as … “The ability to do work” We will define it by providing examples of energy and the effects it has on objects. There are many different types of energy…

Types of Energy We have already talked about many different types of energy. ALL energy can be classified as either Potential Energy or Kinetic Energy.

Gravitational POTENTIAL Energy (GP E ) Gravitational Potential Energy (GP E ) is the stored energy of an object resulting from the object’s position in a system. GP E relies on the height of the object in the system…the higher the object the more GP E it has. If you add GP E to K E + heat you get Total Energy (T E ) TE= GPE + KE + heat

Kinetic Energy (KE) Kinetic Energy (KE) - the energy of motion. The energy associated with moving objects is called kinetic energy (KE), and is often referred to as the most fundamental form of energy. The size of the KE is determined by an object’s speed and its mass.

Review of Energy Forms

Kinetic Energy (KE) - the energy of motion. The energy associated with moving objects is called kinetic energy (KE), and is often referred to as the most fundamental form of energy. The size of the KE is determined by an object’s speed and its mass. A moving baseball has kinetic energy. If you have ever been hit by a pitched ball, you are aware of the energy a moving object can have. Gravitational Potential Energy (GPE) - the stored energy of position. This is energy that an object possesses due to its position. The size of the GPE is determined by the object’s mass and its height above the ground. A person climbing a ladder increases her height above the ground, she increases her GPE. Mechanical Energy

Heat Energy (HE) or Thermal Energy - is the random kinetic energy of particles. Heat energy is the random, and very disorganized, kinetic energy of the particles in a substance. The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. It is a form of energy related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical motion, radiation and thermal conduction.

Chemical Energy (CE) - The energy held in the covalent bonds between atoms in a molecule is called chemical energy. Every bond has a certain amount of energy. To break the bond requires energy, it is called endothermic (energy is absorbed). These broken bonds then join together to create new molecules, and in the process release heat, chemists call this exothermic (energy is released).. If the total heat given out is more than the heat taken in then the whole reaction is called exothermic, and the chemicals get hot.

Nuclear Power Nuclear Power- Nuclear power plants split the nuclei of uranium atoms in a process called fission. The sun combines the nuclei of hydrogen atoms in a process called fusion. Scientists are working on creating fusion energy on earth, so that someday there might be fusion power plants. Salem Nuclear Power Plant

Chemical Energy vs. Nuclear Energy Chemical Energy It is the energy that holds electrons together that move around the nucleus. Happens in the Electron Cloud The energy can be released when the bonds are broken. Small Amount of Energy released Examples Digestion, burning fossil fuels Nuclear Energy It is the energy stored in the nucleus of an atom. Happens in the Nucleus The energy can be released when the nuclei are combined or split apart. Large amount of Energy released Examples Sun,x-rays, Nuclear Power

Electromagnetic Energy –Electromagnetic energy is the energy that comes from electromagnetic radiation. This radiation is composed of waves, such as radio waves and visible light, that move at the speed of light in a way that is suggestive of both waves and particles. Electromagnetic radiation causes both electric and magnetic fields. Only a small part of the electromagnetic field is visible; this part of the electromagnetic spectrum is known as the visible spectrum.

Sound Energy-Sound energy is the energy produced by sound vibrations as they travel through a specific medium. Sound vibrations cause waves of pressure which lead to some level of compression and rarefaction in the mediums through which the sound waves travel. Sound energy is, therefore, a form of mechanical energy; it is not contained in small particles and it is not related to any chemical change, but is purely related to the pressure its vibrations cause. Sound energy is typically not used for electrical power or for other human energy needs because the amount of energy that can be gained from sound is quite small.

Elastic Potential Energy (EPE) - Elastic potential energy is the potential energy of an elastic object (like a bow or a spring) that is deformed under tension or compression (often termed under the word stress by physicists). It happens as a result of a force that tries to restore the object to its original shape, which is most often the electromagnetic force between the atoms and molecules that make up the object. If the stretch is released, it is transformed into mechanical energy.

What’s the Difference between energy transfer and energy transformation? Energy transfer is when the same energy is transferred to another object. When you kick a soccer ball down the field with your moving leg! Energy transformation is when one energy type changes into another type of energy. A rollercoaster that is stopped on top of the hill rolls down the track.

Types of Energy TRANSFER

Energy TRANSFER: Energy transfer - is how the same type of energy is passed from one object to another object. There are only THREE ways that energy can be transferred between objects…

Energy TRANSFER: Method 1: Conduction The transfer of energy through matter by direct contact of particles. Examples: a pot on a stove, a metal spoon in a bowl of hot soup.

Energy TRANSFER : Method 2: Convection The transfer of energy by the movement of gases or liquids. (fluid movement only!!!) Hot fluids will rise while cold fluids will sink… this creates a swirling motion. Examples: Hurricanes, pasta or rice swirling in boiling water, a hot air balloon.

Energy TRANSFER: Method : Radiation The transfer of energy in the form of a wave. (mechanical or electromagnetic waves) Examples: How Earth gets it’s energy from the sun, a microwave oven cooking food, sound.

1. Conduction 3. Convection 2. Radiation

Energy in Systems Energy can move from place to place or change from one type to another… Energy transformation – is changing from one type of energy into a different type of energy. Energy transfer - is how the same type of energy is passed from one object to another object.

Warm up A bowling ball is sitting on a table is pushed off by your little brother. As it falls, it hits a skateboard and rolls across the floor. Explain what happened to both the ball and skateboard. using the terms… Energy Transfer And Energy Transformation Where did the bowling ball get it’s energy from? Your little brother! What kind of energy allowed him to move the ball Chemical

Warm up Answer Bowling Ball KE Energy was transferred to the bowling ball to put the ball in motion. The balls energy was transformed from GPE to KE. Skateboard KE Energy was transferred from the bowling ball to the skateboard. The skateboards energy was transformed from GPE to KE. Is there any friction here? If so, where?

Dropping Golf Balls... You will drop a golf ball and a fuzzy ball from four different heights (25cm, 50cm, 75 cm and 100cm) looking for evidence of energy by a change that is produced by each one.

Let’s Investigate Each person has received a lab paper with 7 Questions and a set of directions from A-D. Work together on this lab! You must do these in order… so if some Questions come first, answer the question BEFORE going on to the direction steps!!! Answer the questions on your lab paper and review your data table. You may discuss the answers and data as a group, but DO NOT copy answers from other groups…write your own! *Helpful Tips* Don’t drop the ball next to the meter stick. Don’t let the ball hit the bottom of pan…redo the drop. Have enough sand to drop the ball into.

Data Table 1.One column is for the golf ball and one column is for the fuzzy ball. 2.Use little ruler to measure the width of the crater in cm. 3.Then Use the ruler to smooth the sand. 4.Record your answers. 5.Clean up when you are finished! Answer post lab questions.* Heights Golf Ball Fuzzy Ball Height (cm) Width of Crater (cm)

Investigation Results 1.) The golf ball does not have any K E since it is not moving. It does not have the ability to move on its own due to its position (sitting in the sand) so it does not have any GP E. If K E = 0J and GP E = 0J then M E is also 0J!!! 2.) The golf ball now has GP E b/c it is above the ground… it now has a height of 25cm!!! It does not have K E though since it is not moving.

Investigation Results 3.) The golf ball got its energy from the person who picked it up and moved it to a height!!! The person TRANSFERRED energy to the ball from themselves when they lifted it!!! This energy came from the person’s muscles. The muscles got their energy from the food you ate. Tracing this flow of energy is called an ENERGY CHAIN.

Investigation Results 4.) The ball dropped from the highest point = 100cm caused the biggest crater. 5.) The variable that changed here was the MASS of the ball. Everything else remained constant (stayed the same). The craters produced by the hollow ball w/ less mass were smaller. Mass affects GP E and K E !!!

Investigation Results 6.) Both of the balls hit the sand at the same speed!!! (In other words, they fall at the same time!!!)…Watch I’ll show you… The difference between the two balls is the amount of energy!!! The more massive ball possesses more energy!!!

Investigation Results 7.) The big point you should have concluded is that MASS affects both GP E and K E. You should have also concluded that the higher the release point, the faster the ball will be traveling when it hits the sand. Gravity speeds up ALL falling objects at the same rate (9.8 m/s 2 ). The greater the speed of the object when it hits the sand, the greater the K E.

Revisiting the Golf ball Lab Where did the golf ball get it’s initial (beginning) energy to even move at all? From the person who initially move the ball. Where did “they” get the energy from? They got the energy from the food they ate that day. What kind of energy is that called? Chemical energy

Revisiting the Golf ball Lab MASS affects both GP E and K E. The higher the release point, the faster the ball will be traveling when it hits the sand. Gravity speeds up ALL falling objects at the same rate (9.8 m/s 2 ). The greater the speed of the object the greater the K E.

Focus Question: What barrier design will stop the car in the shortest distance? Investigating How Forces Transfer Energy Part A: Creating a Barrier Your task is to create a stopping barrier out of dominoes that will stop the car in the shortest distance possible.

Your Mission… 1.You will answer the pre-lab questions (1-4) BEFORE you start the lab. 2. Practice three or four times before you record your trials. 3. You will stack the dominos at the 60cm mark on the ramp. 4. Draw your design in your table.

Pre-Investigation Questions Question #1: What form of energy is present when the car is sitting at the top of the ramp? How do you know this? Question #2: What will happen to the energy of the car as it moves down the ramp? What evidence could you collect to justify your answer? Question #3: When the car strikes the barrier what will happen to the energy of the car? How do you know this? Question #4: Let’s assume we release the car from rest at the top of your ramp. What can you do to be sure that the car strikes your barrier with the same KE in each trial? Explain.

Design your Drawing Draw your design as if you were looking down at it from above. Or draw it from the side if you wish. Place numbers in the blocks if you stacked more than one on top of each other

Your Mission… 5. Record the distance in cm from the 60cm mark to the first domino. 6. If your dominos touch the end wall, your trial doesn't count! 7. You can not have any dominos touching the black wall at the end of ramp.

Data Table Trial # # of blocks used Draw a basic barrier design Stopping distance (cm)

Your Mission… 8. Once you have answered questions 1-4 you may start your lab. 9. After you have completed the domino lab answer questions 5 and 6.

Record your results carefully and be prepared to report to the class the design of your barrier that stopped the car in the shortest distance by exerting the largest stopping force and the answers to the questions asked below. Question #5: What forces are causing the car to stop? Question #6: Why is the stopping distance shorter for some arrangements of blocks than for other arrangements? Conduct your Investigation

Domino Lab Energy Chain You group is to construct an energy chain for the domino lab on a poster. Assume the car is lying on the table. Draw pictures with your energy chain showing one down hill trial of your car. Be sure to include the words transformation and transferring in your energy chain as well as the different types of energy.

Car and Domino Energy Chain Chemical Energy in your body Mechanical Energy in your body Gravitational Potential Energy as the car is lifted onto the track Mechanical Energy as the car rolls down the track Heat Energy from friction Mechanical Energy in the domino barrier Transforms Transforms/Transfers Transforms Transfers Transforms

Newton’s Laws

The cause of it all… What causes acceleration (a change in velocity) to occur? (In other words… what must be applied?) A FORCE!!!

Force What's a force? Any push or a pull on an object to put it into motion. Force can be measured by taking an object’s mass and multiplying it by the acceleration. F = m*a (Units for Force are Newtons: N) 1Newton= 1kg x m/s 2 Units for acceleration are= m/s 2

Force How would you plug the force equation into a power triangle??? (F=ma)

Force Re-arrange the Force equation (F=ma) to solve for mass and acceleration… m = a =

Force There are several types of forces acting on this moving box. What are they?

Force Friction: A force that opposes the motion between two objects in contact with each other. Q: Is it easier to push something across concrete or ice? (WHY?) A: Ice b/c there are less frictional forces.

Unbalanced Forces What would be the NET force (overall force) on the box? = 30 N What direction will the box move? Left

Force Force problems on Pg. 270 Practice #(1-3)

Force problems 1.What is the net force necessary for a 1.6x10 3 kg automobile to accelerate forward at 2.0m/s 2 ? F=ma 1.6x10 3 kg x 2.0m/s 2 = 3200 kg x m/s 2 or… 3200N 2. A baseball accelerates downward at 9.8 m/s 2. If the gravitational force acting on the ball is 1.4N, what is the baseball’s mass? m= f/a 1.4N so…= 9.8 m/s kg x m/s m/s 2 =.142 kg

Force problems 3. A sailboat and its crew have a combined mass of 655kg. If the sailboat experiences an unbalance force of 895N pushing it forward, what is the sailboat’s acceleration? a= f/m 895N so… = 655 kg 895 kg x m/s kg a =1.36 m/s 2

‘Newton’s First LAW LAW 1 (Law of Inertia): An object at rest will remain at rest and an object in motion remains in motion unless acted upon an outside force.Law of Inertia Inertia: The property of an object to resist changes in motion unless acted upon by an unbalanced force. Unbalanced force: A net force that is not equal to zero. Ex. When the car suddenly stops and your body snaps forward.

Newton’s Second LAW LAW 2: The unbalanced force acting on an object equals the object’s mass times its’ acceleration. To accelerate the mass of an object you must apply a force! F= m x a Ex. Any time you move an object

Newton’s Third LAW LAW 3:For every action force, there is an equal and opposite reaction force. Ex. Hitting a homerun off of a pitcher in baseball.

Examples of Newton’s Laws If you are pushing an empty grocery cart with 20N of force… will the grocery cart have the same acceleration if you continue to push it at the same force of 20N when it is full. Which Law and why? A: 2 nd law. NO…the acceleration will be less once the cart is full b/c you have added mass, and a = F/m

Examples of Newton’s Laws What would happen if you were standing on a skateboard and threw a really heavy ball? Which law and why? A 3 rd law. : You will go backwards on the skateboard b/c the ball is pushing you with an equal and opposite force the other way. For every action there is an equal and opposite reaction.

Examples of Newton’s Laws If you are riding on the bus and your books are on the seat next to you… if the bus driver stomps on the brakes…where do your books go??? Which law and why? A: 1 st law. onto the floor… An object in motion stays in motion until acted on by an unbalanced force.

Force Calculations 21. m= 11.5 kg 22. F= 276 N 23. a=.22 m/s m=6.45 kg 25. a= 7.09 m/s F= 22 N

LAW OF CONSERVATION of ENERGY

In the golf ball investigation, can we account for all the energy in the system? If we add up all the PE, KE and any friction, will it equal the total energy (TE) in the system? Yes, scientific evidence leads us to believe that ALL of the energy in any example can be accounted for! But it is not always easy in an open system.

LAW OF CONSERVATION of ENERGY Energy cannot be created or destroyed; it can only be transformed or transferred. Total Energy is all the energy in a system The TOTAL ENERGY (T E ) will always stay the same!!! T E = P E + K E + heat

LAW OF CONSERVATION of ENERGY The TOTAL ENERGY of a system can be measured by adding P E + K E + Heat. T E = K E + P E + heat Q: Where does the heat come from??? A: Friction!!! (Rub your hands together and see what happens!!!)

LAW OF CONSERVATION of ENERGY TE will equal the GPE at the highest point in a system! TE=GPE at the highest point 100 Joules of energy to start 100 Joules of energy at the end! Equal at the mid point! “What you put in, is what you get out!” (TE) NEVER CHANGES in a system! A B C

LAW OF CONSERVATION of ENERGY Let’s look at the pendulum swing. Will it continue to swing with same amount of energy over time? Why won’t the beginning energy ever equal the end energy??? Hint: Can heat be contained in an open system? NO… please remember that energy is not destroyed, but some of it can escape from the system to the surroundings in the form of heat from the rope.

LAW OF CONSERVATION of ENERGY Can any system ever be 100% efficient? Will the beginning energy will ever equal the end energy? NO! There is no such thing as a frictionless system!!!

Energy Ramp Label sections A-E w/ the appropriate level of P E and K E (Assume NO friction) Use the following terms Maximum High Medium Low Minimum zero PE= Max KE= zero KE= Max KE= High KE= Low PE= High KE= Med PE= Min PE= Low PE= Med

Pendulum Energy Transformation Draw this pendulum diagram on white board A. PE=KE? Points 2 and 4 B. PE greatest? Points 1 and 5 C. KE greatest? Point 3 only D. KE lowest? 1 and 5 E. PE lowest? 3 only

PENDULUM E C BD A At which point is the KE greatest? What is the velocity at that point? Point C 5.6 m/s

ENERGY CHAINS Since energy is transferred and transformed all the time, it is helpful to be able to track the “flow” of energy in systems. A map of what happens to energy, where it goes, and how it changes in a system. Energy chains can be created using words, pictures, arrows, or any combination of things that show the movement of energy through a system.

Energy Chains Can you think of how the energy flows through a car? What would you start with? What types of energy transformations are happening? Battery

Energy Chain of a Car Chemical Electrical Thermal Mechanical Kinetic Energy Thermal Energy (Friction) Chemical Sound Energy C 8 H 18 Bonds are breaking in the gasoline, releasing energy

Using Font Size Predict what this car is doing? Coming to a stop! The KE is deceasing over time as it is being transformed in heat and PE energy.

A car stopping as a standard Bar Graph KE HE

ENERGY CHAINS Let’s look at some systems where energy transformation is taking place…(i.e. changing from one type of energy to another type of energy.) Ramps Cars Bungee jumper A Pendulum A Hydroelectric Power Plant

Construct an Energy Chain for a person hitting a softball to the outfield? Include a detailed drawing using the following terms: transferring, transforming, gravity, PE, KE, sound, air resistance, and friction. (assume the ball is on the ground)

Hitting a softball into the outfield (assume the softball is on the ground before it is hit) 1.Chemical E from food to ME to pick up ball. 2.Ball has PE in the air 3.Ball throw in air transform from PE to KE 4.Bat hits ball transfers KE to ball Sound energy / friction given off 5. Ball increases KE 6. Gravity pulls on ball 7. Air resistance slows ball down 8. Ball hits ground (Friction) 9. Balls KE is transferred to dirt as it flies up. 10. KE transformed into Sound energy Friction given when it hits the ground!

POTENTIAL energy (P E ) Potential Energy (P E ) is the stored energy of an object resulting from the position of the object in a system. P E is measured by multiplying the mass of the object times the gravity and then times the height. P E = m x g x h remember…(gravity = 9.8m/s 2 ) Units are Joules!!! (J) 1 Joule= 1kg x m 2 /s 2 PE mostly depends on the height in a system!

POTENTIAL energy (P E ) Examples of objects with high P E : A stretched rubber band Any object high in the air Any compressed object (like a spring) Any object that is high up on cliff/Mountain.

P E Power Triangle Plug P E = m*g*h into a Power Triangle Write the equations when you solve for m and h. M= PE gh h= PE mg

P E Power Triangle Scientists know the acceleration of gravity is 9.8m/s 2

P E Problem Example: A mountain biker rides down a 42m high mountain with 2500 J of GP E. What is the mass of the mountain biker? What’s the formula for GP E ? GP E = mgh Here’s what we know… h = 42m GP E = 2500J Are we missing anything? Gravity 9.8 m/s 2

POWER TRIANGLE If there is a fraction in the formula then the variable at the top of the fraction goes on top of the triangle. Solve for mass So for m= P E mg

S is for Solve : Step 5: Now you need to arrange the data to SOLVE the formula. Put a box around your answer. Take two places past the decimal and Do not round your answer. m = P E mg2500J (kg x m 2 /s 2 ) (42m x 9.8m/s 2 ) = 6.07 kg Example: A mountain biker rides down a 42m high mountain with 2500 J of GP E. What is the mass of the mountain biker?

Answers to P E calculations (1.a) P E = 493,920J or… 4.9 x 10 5 J (1.b) P E = 5,605,600J or… 5.6 x 10 6 J (1.c) P E = J or x 10 3 J (2.) P E = 1.4 x J (3.) h=14.84m (4.) m= 57.82kg

Calculating PE Which apple has more PE? Apples have a mass= 1.5kg Apple “A” height= 15m Apple “B” height= 20m Remember PE=mgh So… Apple “A” PE= 220.5J Apple “B” PE= 294 J So the winner is…Apple “B” Spectrum pg 698 (96-100) Apple “A” Apple “B” 15m 20m Mass of apples = 1.5kg

Answers to P E calculations pg 698 (96-100) 96. PE= mgh(0.14kg)(9.8m/s 2 )(3.5m) PE=4.8J 97.h= PE/mg 6.6 J/ (74kg)(9.8m/s 2 ) h=.0091m 98. PE=mgh (67kg)(9.8m/s2)(2.04m) PE=1339.4J or 1.3x10 3 J 99. m= PE/gh88.9J/ (2.0m)(9.8m/s 2 ) m=4.5kg 100. h= PE/gm.744 J/ (.23kg)(9.8m/s 2 ) m=.33m

PE Calculations PEPE 1. PE= J 2. m= 4.6 kg 3. h= 19.18m 4. PE=7763.8J 5. m=.348 kg 6. h= 24.7 m

Total Energy Remember…Total Energy is all the energy in a system Remember the formula? 1.TE= PE + KE + Heat The heat in a system is the… FRICTION! 2. Total Energy will equal the GPE at the highest point in system. 3. Total Energy NEVER changes in a system! Because…what you put in is what you get out! Let’s see if it works…

Set up a Data Table PEKETE A= B= C= D= E=

Let’s Practice A E B C D Calculate the PE, KE and TE of the ball at the 5 positions. Assume there is no friction The mass of the ball is 8kg. Height = 200m Height = 0m Draw this picture and label it!

Set up a Data Table PE A= 15680J B= 11760J C= 7840J D= 3920J E= 0J TE A= 15680J B= 15680J C= 15680J D= 15680J E= 15680J KE A= 0J B= 3920J C= 7840J D= 11760J E= 15680J

Position APosition BPosition CPosition D Potential Energy (J) 90 Kinetic Energy (J) Heat Energy (J) Total Energy (J) 150 A (h = 50) B (h = 7) D (h = 0) C (h = 30) RFA 4

KINETIC Energy (K E ) Kinetic Energy (K E ) is the energy of any moving object. K E depends on the mass and the velocity (speed) of an object. Only ½ of the mass is used, but velocity is squared… so K E depends mostly on the velocity of the object. K E = ½m * v 2 Units are Joules!!! (J)

Solving KE Problems K E = ½ m * v 2 ***Remember PEMDAS (order of operations) 1 ST Step: Square the v 2 nd Step: Take half the mass 3 rd Step: Multiply 1/2m * v 2

Speed vs. Velocity What’s speed? How fast an object is moving. Then what is velocity? Velocity is speed with direction! Ex. Traveling 90 mi/hr north bound. Page 301 (1a. & 1b.)

Answers to K E calculations Page 301 (1a. & 1b.) 1a.) K E = 630,750 J 1b.) K E = 243,000 J Page 699 (101,103 (51g to ?kg ),105-V=146m/s) J J ,008,000 J.051kg

KE Calculations KE Calculations Remember… K E = ½ m * v 2 KE 7. KE= J 8. KE= J 9. KE= J 10. KE= J 11. KE=1701.5J 12. KE=2795.8J

Bungee Jumper Calculations Person’s mass = 2kg For A-E calculate on white boards: P E, K E, and T E (assume NO friction) Draw the picture and label it. Set up another data table!

P E, K E, and T E Calculations PE A.1960J B.1470J C.980J D.490J E.0J KE A.0J B. 490J C. 980J D. 1470J E. 1960J TE A. 1960J B.1960J C. 1960J D.1960J E. 1960J

HYDROELECTRIC POWER

HYDROELECTRIC POWER PLANT Friction (Thermal energy) Potential Energy Mechanical Energy Electrical Energy Kinetic Energy

HYDROELECTRIC POWER PLANT Production capacity of 12,600 MW (megawatts) and a reliable output of 75 million MW a year. Provides 25% of the energy supply in Brazil and 78% in Paraguay

WORK The Transfer of Energy How does the previous investigation help us to understand how forces transfer energy?

The Transfer of Energy is called WORK Work measures the effects of a force acting over a distance. Work = F*d so… Work= energy transferred The units are N * m = Joules (J) 1 Joule= 1kg x m 2 /s 2 (F) * (d) = Work (1kg x m/s 2 x m)= 1kg x m 2 /s 2

Work Practice Problems Pg ) F = 5200N d = 25m W = F*d W = ? J = (5200N)*(25m) = 130,000J 2.) F = 1N d = 1m W = F*d W = ? J = (1N)*(1m) = 1J 3.) F = 125N d = 14.0m W = F*d W = ? J = (125N)*(14.0m) = 1750J

Work Practice Problems Pg ) F = 165N d =.800m W = F*d W = ? J = (165N)*(.800m) = 132J per stroke 132 J * 30 strokes =3960J

WORK Q: If you try to move a lab table with 12,000N of force and it doesn’t move…How much work have you done? A: NONE!!! Because… W = 0J b/c the distance was 0m and W = 12,000N* 0m = 0J

Work Practice Problems Pg. 285 *Challenge* 5.) d =.5m F = m*g (g = 9.8m/s 2 ) m = 1200kg F = ? N = (1200kg)*(9.8m/s 2 ) = Force= 11,760N F = 11,760N W = F*d d =.5m W = ?J = (11,760N)*(.5m) = 5880J Spectrum Text Book pg (81 and 83)

Work Calculations J J J J J

POWER What’s Power? Power = how much work is done in a given amount of time. 2 people can each bench 100 pounds 10 times. Person one takes 2mins, person 2 takes 1 min. Who is more powerful? Why? A: It takes them less time to do the same amount of work! So we need to account for the time it takes to do work… the equation that measures that is P = W (Units for Power are Joules = Watts) t sec Think about light bulbs! Person 2!

POWER in DUFAS 1. While running track, Drew’s legs do 5780J of work in 183sec. What is his power output? Watts 2. The chain that is pulling a rollercoaster up the first hill does 24,652J of work over a 79sec time interval. What is the power output of the chain? Watts 3. It takes Ms. Webb 20s to apply 23N of force to lift a box 5m. What was her power output? 5.75 Watts

POWER Problems pg. 287 (1-3) Remember a Watt= Joule/seconds 1. P= W3960J=66.0 W T 60.0s 2. P= W900MJ=900 MW T 1s 3. P= W5350J=107 W T50.0s 4a. ***Challenge Question*** Hint* W=F x D W= F(60.0N) x D(12.0m)=720J P= W720J=36 W T 20.0s Spectrum Text Book Pg 698 (86 and 89)

Power Calculations Power 13. P=.84 watts 14. P= 6.6 watts 15. P=.003 watts 16. P=143,987.3 watts

Elastic Potential Energy Elastic Potential energy can be determined from the objects stretch squared and the constant that reflects the elasticity of the material. So what’s this mean in English? Elastic EP E = 1/2kx 2 Elastic PE is measured in Joules(J)

Elastic Potential Energy Elastic PE= 1/2kx 2 K=spring constant N/m X= amount stretched or compression Ex:(compressed spring, pulled rubber band)

Elastic Potential Energy Problem Remember… Elastic PE= 1/2kx 2 The elastic force constant stored in a drawn bow is 100 N/m. The bow is drawn to pull the arrow back a distance of 0.5 meters. Calculate the elastic potential energy stored in the drawn bow. In DUFAS K= 100 N/m 2 50 N/m X=(.5m) 2.25m 2 50 N/m x.25m 2 EP E =12.5 J

Elastic Potential Energy Problem The elastic force constant of a spring in a toy is 550 N/m. If the spring is compressed.12 m, compute the elastic potential energy stored in the spring. In DUFAS K= 550 N/m N/m X=(.12m) m N/m x.0144m 2 EP E =3.96 J

Elastic Potential Energy Problem The elastic force constant of a rubber balloon is 63 N/m. If the balloon is stretched.13 m when blown up, calculate the elastic potential energy stored in the rubber balloon. In DUFAS K= 63 N/m N/m X=(.13m) m N/m x.0169m 2 EP E = J

Elastic Potential Energy Calculations 17.75J J ,214.5 J 20.17,650.5 J

SAFER Crash Barriers An excellent application of these concepts is the “soft walls” used by major racing facilities across the nation (Dover International Speedway being one of these). The new SAFER (Steel And Foam Energy Reduction) barriers have revolutionized the sport of automobile racing and made it much safer for both the drivers and the fans.

So how do SAFER barriers absorb energy?* The barriers move upon impact so that the KE of the car is transferred to a very large area of the wall (a large portion of the wall flexes upon impact). The key idea is that no one portion of the wall receives a large amount of the car’s KE. The KE of the flexing soft wall is then transferred to the outer permanent wall and support structure. The materials that make up the wall are not elastic. Imagine what the collision would be like if the wall was elastic! Still other portions of the car’s initial KE are transformed into heat energy and sound energy.

Forces That Transfer Energy Making Crash Barriers

Crumple Zones

Collapsed Crumple Zone

Good Crumple Zone

Scientific Notation Think about the number line:

Scientific Notation When you see a number like: 3.46 E -4 m Come up on your calculator… Here’s what that means…

3.46 E -4 … The E -4 means x10 -4 And here is how you translate that into a number. The exponent (-4) tells you how many times to move the decimal point (4). And because it is negative (-), to move it left!)

Scientific Notation So for 3.46 E -4 g You will move the decimal point 4 times to the left. (negative is to the left on the number line!!!) = g Make sure you put units on it also! = g

Scientific Notation Let’s practice: Change 4.86 E 3 kg into a regular number… Need to move the decimal 3 times and to the right because the 3 is positive. = 4860 and don’t forget units! = 4860 kg

Scientific Notation YOUR TURN: 1.) E -2 m 2.) E 4 kg 3.) x10 -6 g 4.) x10 5 cm 3 ANSWERS: 1.) m 2.) kg 3.) g 4.) cm 3 When you move the decimal to the left it is negative. And When you move the decimal to the right it is positive!

This graph shows a ball rolling from A to G. Which letter shows the ball when it has the maximum kinetic energy?

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