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Physics

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2. Electrical Energy How do humans generate electricity? What might be some “other” sources of energy? Most methods involve heat and a turbine. These sources of energy are not useable without transforming them into electricity (you can’t use petroleum to make your blender work). Power plants typically harness heat and use that to drive a generator which in turn creates electrical energy. solar, geothermal, wind, tidalMost methods involve heat and a turbine. These sources of energy are not useable without transforming them into electricity (you can’t use petroleum to make your blender work). Power plants typically harness heat and use that to drive a generator which in turn creates electrical energy. solar, geothermal, wind, tidal

3. Electrical Energy What do we use it for? Estimate the percentage used to: drive engines or to generate electricity provide heating Generate electricity w/o burning We don’t ‘use’ electricity. We convert it to something more useful like heat, motion, light or sound. Electricity, transportation, heating drive engines or to generate electricity 60% provide heating30% Generate electricity w/o burning 10%We don’t ‘use’ electricity. We convert it to something more useful like heat, motion, light or sound. Electricity, transportation, heating drive engines or to generate electricity 60% provide heating30% Generate electricity w/o burning 10%

4. Electrical Energy How much does it cost? ~10 cents per kWh How much does the US consume per year compared to the rest of the world? ~25% of the total amount (we actually consume more than we produce) Cost is relative…as electricity customers, we can relate to our monthly bill (ask for some examples and reasons for variations) Environmental cost-water, air, land, habitat, etc… There is a general lack of conservative thinking when it comes to energy consumption in the US Since the U.S. only makes up 6% of the world’s population, and we use 25% of the world’s energy, we could consider ourselves “energy hogs “Cost is relative…as electricity customers, we can relate to our monthly bill (ask for some examples and reasons for variations) Environmental cost-water, air, land, habitat, etc… There is a general lack of conservative thinking when it comes to energy consumption in the US Since the U.S. only makes up 6% of the world’s population, and we use 25% of the world’s energy, we could consider ourselves “energy hogs “

7. Types of Energy Electrical – energy of electromagnetic interactions Mechanical – energy of objects and machines Kinetic and Potential Chemical – energy of chemical reactions Nuclear – energy of nuclear interactions Radiant – energy that travels through space Ask for other names for energy types not listed and see if they are easily categorized into this system. Stress that this is only one way to define energy types. For example, thermal energy is really a form of kinetic energy; hence, it would be classified as mechanical. Also, light is a form of radiation that travels through space; therefore, it is radiant energy. Ask for other names for energy types not listed and see if they are easily categorized into this system. Stress that this is only one way to define energy types. For example, thermal energy is really a form of kinetic energy; hence, it would be classified as mechanical. Also, light is a form of radiation that travels through space; therefore, it is radiant energy.

8. Energy Conversion Converting energy from one type to another requires Work. Work is defined as a transfer of energy. EXAMPLE: We can use a force to transfer energy to an object IMPORTANT NOTE: We say conversion because energy is never created nor destroyed.IMPORTANT NOTE: We say conversion because energy is never created nor destroyed.

9. How fast is the Energy Converted? Work, in a mechanical sense, is a force applied over a certain distance. This generally results in a change in the kinetic energy of an object and/or a change in its potential energy. But how fast you convert the energy depends on the time it takes you to do the work…AHA! That’s a rate. Power is the rate of energy conversion. Ask where they have heard the term Watt before. Light bulb, microwave Explain that this rating (# of watts) tells you how many joules of energy are consumed each second while in operation Ex: 100 watt light bulb uses 100 Joules of electrical energy per second and emits 100 Joules of heat and light per second How would this compare to a 200 Watt light bulb? It would emit twice as much energy per unit of time.Ask where they have heard the term Watt before. Light bulb, microwave Explain that this rating (# of watts) tells you how many joules of energy are consumed each second while in operation Ex: 100 watt light bulb uses 100 Joules of electrical energy per second and emits 100 Joules of heat and light per second How would this compare to a 200 Watt light bulb? It would emit twice as much energy per unit of time.

10. How powerful are you? HO 5.1 Materials: Stairs Meter stick Timer Calculator What does that mean, “powerful”? Webster’s: the ability to produce effectWhat does that mean, “powerful”? Webster’s: the ability to produce effect

11. How Powerful are you? As a class, measure the height of a flight of stairs (from the floor to the topmost stair) and record this value in meters. Carefully travel up the stairs while your partner records the time it takes you to ascend. Stress the need for caution so no one slipsStress the need for caution so no one slips

12. How Powerful are you? What force did you apply to travel up the stairs? You had to apply a force equal to your weight. Calculate your weight in Newtons (1 lb = 4.45 N) Multiply your weight by the height of the stairs (in meters) to determine the total work done. Divide this number by the time (in seconds) that it took you to ascend the stairs to determine your power. Convert your power in Watts to Horsepower (1hp = 746W). Are you more or less powerful than a horse?, a lawnmower?, a sports car? What could you do to increase your power? So if you weigh 100 pounds, that is 445 N. So if the flight of stairs were 2m tall, this gives 445 N * 2m = 990J So if it took 3 seconds to go up the flight of stairs, this gives 990J/3 sec = 330W 330W * 1 hp/746W = 0.44 hp Horse = 1 hp Lawn mower = 5 hp Sports car = 200 hp To increase one’s power, decrease the time, and/or increase the weight.So if you weigh 100 pounds, that is 445 N. So if the flight of stairs were 2m tall, this gives 445 N * 2m = 990J So if it took 3 seconds to go up the flight of stairs, this gives 990J/3 sec = 330W 330W * 1 hp/746W = 0.44 hp Horse = 1 hp Lawn mower = 5 hp Sports car = 200 hp To increase one’s power, decrease the time, and/or increase the weight.

13. Energy Conversion In order to move your body up the stairs, you had to perform work. Recall that work is a transfer of energy. What type of energy did you start with at the bottom of the stairs? What kind of energy did you have at the top of the stairs? Were there any intermediate forms of energy present while you were climbing? This is an oral evaluation. At the bottom, chemical due to the stored up metabolic energy in your body At the top, potential due to your increased height above the rest position (ground floor) While moving, kinetic and increasing potential as you climb.This is an oral evaluation. At the bottom, chemical due to the stored up metabolic energy in your body At the top, potential due to your increased height above the rest position (ground floor) While moving, kinetic and increasing potential as you climb.

14. Mechanical Energy What kinds of energy would you expect to be present in the situation depicted below? What energy conversions are taking place? Rotational, Vibrational, and Translational Kinetic Energy in his motion Potential Energy because of his height off the ground Chemical Energy due to the fuel in his tank Mechanical Energy in the form of sound is released Accept all reasonable answers for energy conversion.Rotational, Vibrational, and Translational Kinetic Energy in his motion Potential Energy because of his height off the ground Chemical Energy due to the fuel in his tank Mechanical Energy in the form of sound is released Accept all reasonable answers for energy conversion.

15. Ramp Racers HO 5.2 Materials: carts, ramps, ramp stands, protractors, meter sticks, masses, timers As a class, determine what factors influence the time taken for a cart to travel down the ramp. Themes to explore include (one per group): Release point Mass Incline Ramps are one of the simplest mechanical systems to examine. First, we need to explore the motion of objects on a ramp. Afterwards, we’ll examine the motion in terms of energy transformations. Assign each group to explore a single theme. Ramps are one of the simplest mechanical systems to examine. First, we need to explore the motion of objects on a ramp. Afterwards, we’ll examine the motion in terms of energy transformations. Assign each group to explore a single theme.

16. Ramp Racers Each group should: Hypothesize about the particular effect they are going to investigate Design an experiment to test this hypothesis Make observations and collect data in a table Evaluate results Report findings to the class Hypothesis: A prediction that can be verified or refuted. Good hypothesis: The dimensions of a material increase as the temperature increases. (sometimes WORNG!) Bad hypothesis: Albert Einstein was the greatest scientist EVER!Hypothesis: A prediction that can be verified or refuted. Good hypothesis: The dimensions of a material increase as the temperature increases. (sometimes WORNG!) Bad hypothesis: Albert Einstein was the greatest scientist EVER!

17. So what’s the effect of different: Masses Carts accelerate at the same rate due to an elegant balance between Net Force and inertia…remember Newton’s Second Law Release point ½ the distance to travel doesn’t imply ½ the time because our velocity is no longer constant Angle of incline Steeper angle leads to greater acceleration…what about an angle of zero, an angle of 90? For masses, the ratio of force to mass for different carts is still the same number, the acceleration. For release point, distance traveled under constant acceleration does not linearly depend on time. It’s related to the square of the time. For an angle of incline equal to zero, there is no net force acting to move the cart down the ramp. Therefore, acceleration equals zero. For an angle of incline equal to 90 deg, the net force acting to move the cart down the ramp is equal to the weight of the cart. Therefore, acceleration is the same as gravity, about 10 m/s2. For masses, the ratio of force to mass for different carts is still the same number, the acceleration. For release point, distance traveled under constant acceleration does not linearly depend on time. It’s related to the square of the time. For an angle of incline equal to zero, there is no net force acting to move the cart down the ramp. Therefore, acceleration equals zero. For an angle of incline equal to 90 deg, the net force acting to move the cart down the ramp is equal to the weight of the cart. Therefore, acceleration is the same as gravity, about 10 m/s2.

18. Motion in Terms of Energy Masses: A more massive cart would have greater amount of potential energy compared to an empty cart on identical ramps. Therefore, the more massive cart would have greater kinetic energy at the bottom of the ramp. Be careful! This doesn’t mean the heavier cart is moving faster. Release Point: Potential energy is directly related to height above the rest position. If the object is not placed at the top of the ramp, it starts with less potential energy. Therefore, it has less kinetic energy when it reaches the bottom. Angle of incline: Potential energy is directly related to height above the rest position. If the angle of incline of the ramp is increased, the object starts with more potential energy. Therefore, it has more kinetic energy when it reaches the bottom.

19. Potential Energy HO 5.3 At the top of the ramp, the stationary object has only Potential Energy. The formula for the amount of PE is: Potential Energy = mass*gravity*height PE=mgh g = 9.8 m/s2

20. Potential Energy Example Assume the object has a mass of 5 kg and the height of the ramp is 0.5 meters. How much PE does the object have relative to the floor? PE=mgh PE = (5kg)(9.8m/s2)(0.5m) PE = 24.5 Joules

21. So What Force Does Work to Convert potential energy to kinetic energy? We need a free body diagram.

22. Net Force Vector sum of all forces acting on an object

23. Kinetic Energy When the object reaches the bottom of the ramp, the work done by the Net Force has converted the Potential Energy into Kinetic Energy, i.e. energy of motion. The formula for Kinetic Energy is: KE = ½ * mass * velocity2 KE = ½mv2

24. Kinetic Energy Example Assume the object has a mass of 5 kg, and a velocity of 2 m/s at the bottom of the ramp. How much kinetic energy does the object have? KE = ½mv2 KE = ½(5kg)(2m/s)2 KE = 10 Joules

25. Energy Transformations Energy conservation and conversion are important considerations for all systems Mechanical systems have both potential energy and kinetic energy When work is done, energy changes from one form to another EX. Stored Gravitational Potential Energy is converted into Kinetic Energy when the Earth pulls a ball released from some height down to the floor. Energy is neither created nor destroyed during any process, only changed in form

26. Reading Assignments HO 5.4 NSES 149, 154-155;179-180 BSL 81-86, 194 Integrated Science Chapter 3:p47-59

27. Concepts and Questions Integrated Science Applying the Concepts 1-2, 4, 6, 8-11 Questions for Thought 1, 3, 5, 8, 12 Parallel Exercises Group A: 1,3,11,12