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Science 10

Science 10. Aim: Algebra, Motion Graphs, and Kinetic and Potential Energy . Agenda. Algebra, Motion Graphs, and Kinetic and Potential Energy Practice calculations Homework: read p. 155-160 Next class. Working with Formulas.

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Science 10

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  1. Science 10 • Aim: Algebra, Motion Graphs, and Kinetic and Potential Energy

  2. Agenda • Algebra, Motion Graphs, and Kinetic and Potential Energy Practice calculations • Homework: read p. 155-160 • Next class

  3. Working with Formulas Sometimes the variable you are looking for is mixed in with the other variables… Example: A = 15 C = 6 Solve for B D = 2 … so you must Rearrange the Formula so that variable is alone on one side of the equals sign A = BC D B =

  4. A = BC D Example: A = 15 C = 6 Solve for B D = 2 Two ways to do this type of rearrangement question: Method1: - Rearrange the formula and then replace the symbols with their number values Method 2: - Replace the symbols with their number values, then rearrange Method 1 is a lot less messy!

  5. AN IMPORTANT RULE!!When you Rearrange Formulas… …WHAT YOU DO TO ONE SIDE, YOU HAVE TO DO TO THE OTHER

  6. Math Operation Opposites: Multiply Divide Add Subtract Squared Square Root

  7. Math Operation Opposites Multiply Divide Add Subtract Squared Square Root Solve for B in the Following Formulas: A = B + C A = B - C A = BC A = B C A = B - CD A = B2

  8. SOLVE FOR B… A = 15 C = 6 D = 2 A = BC D

  9. SOLVE FOR B… A = 15 C = 6 A = C + B2

  10. WORK INDIVIDUALLYFIND THE ACCELERATION? 60 50 40 30 20 10 0 Velocity (m/s[N]) 0 1 2 3 4 5 6 7 8 Time (s)

  11. Graphs and Motion

  12. Graphs and Motion Graphs can be used to show different types of motion. 3 types of graphs that can show the same type of motion:  Distance vs. Time  Velocity vs. Time  Acceleration vs. Time

  13. Type of Motion:An Object or Body at Rest Distance vs. TimeVelocity vs. Time Acceleration vs. Time

  14. Type of Motion:An Object of Body in Uniform Motion Distance vs. TimeVelocity vs. Time Acceleration vs. Time

  15. Type of Motion:An Object or Body in Positive Uniform Motion Distance vs. TimeVelocity vs. Time Acceleration vs. Time

  16. Type of Motion:An Object or Body in Negative Uniform Motion Distance vs. Time Velocity vs. Time Acceleration vs. Time

  17. Seat Work: • Determine the Acceleration 60 50 40 30 20 10 0 Velocity (m/s[N]) 0 1 2 3 4 5 6 7 8 Time (s)

  18. KENETIC AND POTENTIAL ENERGY

  19. KENETIC ENERGY (KE or EK) • is the energy of motion. • The amount of kinetic energy depends on the speed and mass of the object.

  20. KE Formula… Ek = ½ mv2 = = mv2 2 Ek = kinetic energy (J) m = mass of object (kg) v = speed of object (m/s) Units: Ek = ½ mv2 (J) = ½ (kg)(m/s)2

  21. Using the Formula ( Ek = ½ mv2 ) 1) A car with a mass of 1500 kg is moving at a speed of 14 m/s. What is the kinetic energy of the car? 2) A hockey puck has a mass of 0.21kg. If the hockey puck has 73J of kinetic energy, what is its speed?

  22. Work • The transfer of mechanical energy from one object to another W = Fd

  23. Work  can either add or remove kinetic energy from an object. Positive Work (adding KE ): A pitcher does work on a ball  transfers kinetic energy to the ball.

  24. Negative work • is done if you remove kinetic energy from an object (if a force is applied opposite to the object’s motion, or the object slows down). • Example: catching the ball removes kinetic energy causing it to slow down

  25. POTENTIAL ENERGY (PE) • is stored energy.

  26. Forms of potential energy • Elastic • Chemical • Nuclear • Gravitational

  27. Elastic Potential Energy • An object is elastic if it always returns to its original form after its been distorted • Work done on an elastic object to distort it gives it elastic potential energy • E.g. bungee cords

  28. Chemical Potential Energy • chemicals that lose little energy when bonds are formed have the potential of releasing even more energy by undergoing chemical reactions This chemical reaction releases thermal energy (heat)

  29. Chemical Potential Energy Glucoseis the principal form of chemical energy for plants and animals… the reaction that breaks down glucose and supplies the energy is called the CELLULAR RESPIRATION reaction C6H12C6 + 6O2  6CO2 + 6H2O + Energy

  30. Nuclear Potential Energy • very large nuclei (uranium and plutonium) have the potential to split into two smaller nuclei and release large amounts of energy

  31. Nuclear Potential Energy • very large nuclei (uranium and plutonium) have the potential to split into two smaller nuclei and release large amounts of energy • Einstein said during a nuclear reaction, some of the mass of the reactants was converted into energy (mass of products does not = mass of the reactants in nuclear reactions)

  32. Gravitational Potential Energy • the potential energy an object has due to its location above the Earth’s surface (a mass at a height)

  33. Gravity… • is a property of all objects with mass. • any two masses attract each other with a gravitational force • this force is not noticeable unless one of the masses is very large (moon, planet, star) • if there is no force opposing the force of gravity on an object, its motion will change

  34. Gravity… • if there were no air friction, all objects near Earth’s surface would fall with the same acceleration, called the acceleration due to gravity (g = 9.81 m/s2) http://www.youtube.com/watch?v=5C5_dOEyAfk

  35. Weight • is the force of gravity acting on an object Weight ≠ Mass

  36. Weight • is the force of gravity acting on an object Weight ≠ Mass Mass = Quantity of Matter in an Object

  37. Weight • is the force of gravity acting on an object • Force of gravity (weight) (N ) • m = mass (kg) • g = acceleration due to gravity (9.81m/s2)

  38. When all of the work done on an object gives it gravitational potential energy, the work done is equal to the gravitational potential energy gained.

  39. since • Ep = gravitational potential energy (J or ) • m= mass (kg) • g = acceleration due to gravity (9.81m/s2) • h = Change in height (m) since Gravitational POTENTIAL ENERGY FORMULA!

  40. E.g. The shelf in your locker is 1.8 m above the floor. If your science book has a mass of 1.2 kg, what is its gravitational potential energy relative to the floor if it is sitting on the shelf? • E.g. If you did 565 J of work on a 12 kg box by carrying it up a flight of stairs, how high is the flight of stairs?

  41. Efficiency The second law of thermodynamics says: No process can be 100% efficient. Some energy will always remain in the form of thermal energy. During any process, some energy is always transformed into a form that is not useful. This energy is often said to be wasted.

  42. USEFUL ENERGY: Energy that performs a task WASTE ENERGY: Energy converted during process into a form that is not useful, such as heat Example: Light Bulb  useful energy = light  wasted energy = heat

  43. is a ratio of the useful energy output to the total energy input. In other words, the percentage of the energy we put in to a system that is converted into the type of energy we want. Efficiency To use the equation, you must be able to identify the useful energy output and the total energy input .

  44. Example: You climb up the steps of a slide at the waterpark. The top of the slide is 100 m above the pool below. Your mass is 55.0 kg and you are traveling at a speed of 4.30 m/s at the bottom of the slide. Calculate the efficiency of the transformation of gravitational potential energy into kinetic energy. → Gravitational potential energy • 1) Energy Input = 53 955 J

  45. Example: (Continued) • 2) Energy Output → Kinetic Energy = 508.475J

  46. Example: (Continued) • 3) Calculate Efficiency = 0.942%

  47. Simple Systems • A simple pendulum is a simple example of energy transformations

  48. Energy Transformations Input Energy Converter Useful Output +Waste Energy EX AM PLES

  49. Calculating Efficiency Class Practice Problem • You use the chemical energy obtained from your food to pedal your bicycle up a steep hill, thus gaining gravitational potential energy. You then coasted down the hill, transforming the gravitational potential energy into kinetic energy. Suppose the you pedalled up a hill and gained a vertical distance of 25 m. You turned around and coasted down the hill. At the bottom of the hill, you were coasting at a speed of 13 m/s. If the combined mass of yourself and your bicycle is 68 kg, what was the efficiency of the transformation of your gravitational potential energy into kinetic energy?

  50. Practice Problems Do practice problems page 227 # 1-9 (odd)

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