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Sec 4 Chapter 3


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Notes from the Observatory textbook. Summarizes what the students should know.

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Sec 4 Chapter 3

  1. 1. Chapter 3 Different Forms of Energy
  2. 2. A Quick Review • What are the following? 1. Energy transformation 2. Forms of energy 1. Chemical 2. Thermal 3. Mechanical 4. radiation 3. Temperature 4. Mass
  3. 3. 1 – What is energy? • Energy occurs in many forms and from many sources. • See Table 3.1 on page 70 • Energy is the ability to do work or effect change. • The International System of Union (SI) expresses energy in joules (J) 1 J = 1N/m
  4. 4. 1.1 – The Law of Conservation of Energy • Energy Transfer is the movement of energy from one place to another. • Energy Transformation is the changing of energy from one form to another. • Law of Conservation of Energy: Energy can be neither created nor destroyed; it can only be transferred or transformed.
  5. 5. 1.2 – Energy Efficiency • Energy can be changed from one form to another. • Energy conversion rarely results in all of the energy being converted into useful energy. • Energy efficiency is the percentage of energy consumed by a machine or system that was transformed into useful energy. Energy efficiency = amount of useful energy X 100% amount of energy consumed
  6. 6. Only 12% of the chemical energy from gasoline is actually used by the wheels to make the car move
  7. 7. 1.3 Thermal Energy • Random movement of all the microscopic particles in a substance. • Factors Affecting Thermal Energy (Fig. 3.4) Factor Factor variation Results Number of particles More particles Increased thermal energy Fewer particles Reduced thermal energy Temperature Higher temperature Increased thermal energy Lower temperature Reduced thermal energy
  8. 8. • Thermal energy is the energy contained in a substance, determined by the number of particles in the substance and the temperature • How can we determine the number of particles? – Find the mass!! • Heat is the transfer of the thermal energy between two environments with different temperatures. – Heat always moves from the warmer environment to the cooler environment
  9. 9. • The relationship between heat and thermal energy is expressed by this equation Q=ΔEt Q = the heat (in J) ΔEt= the variation in thermal energy (in J)
  10. 10. • How are heat and temperature different? • Temperature is a measure of the degree of agitation of the particles of a substance • Heat depends on the degree of agitation and the mass of the substance
  11. 11. Specific Heat • Oil heats faster than water. Why? • Water has a specific heat of 4.18 J/g0C • Vegetable oil has a specific heat of 2.00 J/g0C • Oil heats easier than water – gets warm faster with the same amount of heat applied. • What does this really mean???
  12. 12. What it means… • To raise the temperature of 1 g of water by 1 0C requires 4.185 J of energy. • To raise the temperature of 1 g of oil by 1 oC requires 2.000 J of energy. • It requires 2.09 times as many joules to raise the temperature of the water .
  13. 13. Substance Specific Heat Capacity (J/g0C) H2 gas 14.267 He gas 5.30 H2O (l) 4.184 Ethyl alcohol 2.460 Vegetable oil 2.000 Air 1.020 Concrete 0.88 sand 0.290 Silver 0.240 Gold 0.129
  14. 14. • The specific heat of hydrogen (H2) is 14.26 • The specific heat of air is 1.02 • Is air or hydrogen easier to warm up? • Air by a factor of 14!!!! • Hydrogen requires 14 X as many joules to heat the same amount!!
  15. 15. Why does sand feel so hot on the beach on a warm summer day? • Air - 1.020 • Sand - 0.290 • Do the math: 1.020/0.290 = 3.52 Air requires 3.5 times as many joules of energy to heat up. A smaller specific heat capacity means the substance requires less energy to heat it up.
  16. 16. Substance Specific Heat Capacity (J/g0C) H2 gas 14.267 He gas 5.30 H2O (l) 4.184 Ethyl alcohol 2.460 Vegetable oil 2.000 Air 1.020 Concrete 0.88 sand 0.290 Silver 0.240 Gold 0.129
  17. 17. • Which substance on the list heats the easiest? • Gold!!!
  18. 18. • Checkup page 99 • Do questions 1 to 6 • Read pages 79 – 87 - Motion and Forces
  19. 19. • When two different substances are heated, their temperature increases but not necessarily at the same rate. • The specific heat capacity corresponds to the amount of thermal energy required to raise the temperature of one gram of a substance one degree Celcius. • The heat absorbed or released by a given substance can be calculated!!!
  20. 20. Q = mcΔT • Q = the heat present in the substance • m = the mass ( g) • c = the specific heat capacity of the substance (J/gοC) • ΔT = the change in temperature (οC) • ΔT = Tf –Ti – Tf is the final temperature and Ti is the initial temperature
  21. 21. A beaker containing 100 g of water is heated from 20oC to 44 0C. Q = 100 x 4.19 x 22 = 10 056 J A beaker containing 100 g of vegetable oil is heated from 20oC to 44 0C. Q = 100 x 2.00 x 22 = 4 800 J A beaker containing 200 g of water is heated from 20oC to 44 0C. Q = 200 x 4.19 x 22 = 20 112 J A beaker containing 100 g of water is cooled from 20oC to 44 0C. Q = 100 x 4.19 x -22 = -10 056 J Remember that the ΔT = Tf – Ti, which in the first 4 examples is 44-20 = 24 There is an error in your textbook!!!! Find the error.
  22. 22. 1.4 – Kinetic Energy • Kinetic energy is the energy an object posses due to its motion. • Energy of motion!!!! • Items at rest have no kinetic energy!!! • The amount of kinetic energy depends on two variables: 1. Mass 2. Velocity
  23. 23. Ek = ½mv2 Ek = the kinetic energy of the object (J) m = mass of the object (kg) v = velocity of the object (m/s) • A car weighing 2500 kg travels at 50 km/h (about 14 m/2) Ek = ½ mv2 ½ x 2500 kg x (14 m/s )2 = 245 000 J
  24. 24. • A car weighing 2500 kg travels at 100 km/h (about 28 m/s). Ek = ½ x 2500 x (28)2 = 980 000 J • A minivan weighing 5000 kg travels at 50 km/h ( 14 m/s). Ek = ½ x 5000 x (14)2 = 490 000 J
  25. 25. 2 – Motion and Forces 2.1 - Motion • The main variables to describe the motion of an object are: 1. Speed (velocity) 2. Distance travelled 3. Travelling time • There is a mathematical relationship between these values: v = d Δt v= velocity (m/s) d= distanced travelled (m) Δt = travelling time (s)
  26. 26. Finding the velocity using a graph • A position-time graph shows us the time (s) and the distance (m). • The steeper the slope the greater the velocity 0 2 4 6 8 10 12 14 0 2 4 6 Average Velocity Average Velocity Distance (m) Time (s) V = d/Δt V = 6m/2s V = 3 m/s
  27. 27. 2.2 Forces and Change • Pushing or pulling in object is exerting a force on the object. • A force is an action that can change the motion of an object, or deform the object, by pushing or pulling on it. • A force is always exerted by one body on another, and in one direction.
  28. 28. • The force can be represented graphically with an arrow. • The following 4 points must be taken into account 1. The horizontal or vertical line of action is represented by a straight (dotted) line 2. The direction of the applied force is represented by the arrow 3. The magnitude (size) of the force is represented by the length of the arrow. 4. The point of application of the force corresponds to the starting point of the arrow.
  29. 29. 350 20 NA simple diagram to show the same information
  30. 30. 350 350 20 N 10 N Shows two different forces – different lengths for the lines. The angle is very important for determining the force.
  31. 31. • Force is measured in Newtons (N) • A Newton is the force required to make a one kilogram object accelerate at a rate of 1 m/s2.
  32. 32. A force can change the motion of an object in different ways: 1. A force acts on a stationary object by giving it a certain velocity. A force can increase the velocity of an object already in motion if the force is exerted in the same direction as the motion – causes the object to accelerate. 2. A force can reduce the velocity of an object if the force is applied in the opposite direction to the motion. The object may slow down or stop. This is deceleration or negative acceleration. 3. A force can also modify the trajectory of an object, modify the course. This happens when a force is applied on one side of a moving object. This is also a form of acceleration.
  33. 33. 2.3 Types of Forces • There are four main categories: 1. Gravitational force 2. Electromagnetic force 3. Strong nuclear forces 4. Weak nuclear forces • These forces can act across a distance and direct contact between two bodies is not required!
  34. 34. Gravitational Force • This is the force of attraction between all objects as a result of their masses and the distance between the objects. • Heavier objects have a stronger gravitational force. • Objects that are farther away have weaker gravitational forces – weak attraction. • The Earth has a large mass and is close by so it has a strong gravitational pull on objects on the surface of the Earth
  35. 35. • The gravitational pull on all objects, on the surface of the Earth is 9.8 m/s2. • Gravitational pull is toward the center of the Earth so the farther you move from the center of the Earth, the smaller the gravitational pull exerted on an object.
  36. 36. • Gravitational force explains falling objects, celestial bodies and tides. – The force of gravitational pull exerted by the moon affects tides • Discussed in detail in Chapter 7
  37. 37. The relationship between mass and weight!! • In science, they do not mean the same thing. • Mass is a measure of the quantity of matter in an object. • Weight is a measure of the gravitational force acting on an object. – w = Fg = mg w= weight in N Fg = gravitational force in N m = mass in kg g = gravitational field intensity in N/kg
  38. 38. • Example: If you have a mass of 60 kg on the surface of the Earth you will weigh 60 x 9.8 =588 N • On the moon: 60 x 1.67 = 100 N • Venus: 60 x 8.62 = 517 N • Jupiter: 60 x 25.87 = 1552 N
  39. 39. Electromagnetic Force • A force of attraction or repulsion between two objects with electrical charges or with magnetic poles. • Responsible for the bonds between atoms in a molecule. • Also responsible for muscle tension, magnetic phenomena, and the movement of electric current. • Electromagnetic forces are also responsible for contact forces. • These forces are the result of direct contact with an object
  40. 40. • The table resists the pressure of the book by opposing it with an electromagnetic contact force equal to the weight of the book.
  41. 41. The force of friction • Friction is a form of contact force. • Wears machine parts out but also allows us to walk and do many other every day things. • Air resistance is also a force of friction. • Friction occurs between two objects whose surfaces are not perfectly smooth, when they come into contact. • Friction must be overcome in order for an object to be in motion.
  42. 42. • Friction is a force that prevents two objects from slipping over each other when they come into contact. • Friction depends on two factors 1. The nature of the surfaces in contact – rougher surfaces = greater friction 2. The intensity of the pressure of each surface on the other - higher pressure = greater friction • Slip is the opposite of friction
  43. 43. Strong and weak nuclear forces • These act within the nucleus of the atom • The force is non-existent outside of the nucleus. • Strong nuclear force: – High intensity force of attraction that holds protons and neutrons together • Weak nuclear forces: – Low intensity force of attraction - radiation
  44. 44. 2.4 – The Equilibrium of Two Forces • Every object is constantly to at least one force: – GRAVITY • Most objects are subjected to several forces at the same time. • The resultant force (net force) is a virtual force whose action is equal to the combination of all the forces applied simultaneously to an object.
  45. 45. • When the resultant force is zero, the object is at equilibrium. • The motion of the object remains constant.
  46. 46. 3 – Forces in Fluids • What is pressure? – Force/area • What is density? – Mass/volume • Pressure is the force applied perpendicular to an object per unit of surface area. • Pressure is measured in Pascals (Pa)
  47. 47. P = F 1 Pa = 1 N A P = pressure in Pa F = force perpendicular to the surface in N A = surface area subjected to the force in m2 1 m2
  48. 48. • Pressure in a liquid depends on two factors: 1. The depth 2. The density Figure 3.28 Factor Factor Variation Result Depth Increased depth in the liquid Increased pressure Reduced depth in the liquid Reduced pressure Density Higher liquid density Higher pressure Lower liquid density Lower pressure
  49. 49. • Pressure in a gas depends on the number of collisions between the gas particles. • More collisions = greater pressure. • There are 3 factors that influence the number of collisions: 1. Temperature 2. Volume 3. Number of particles
  50. 50. Figure 3.31 Factors influencing pressure in a gas Factor Factor Variation Result Temperature Higher gas temperature Increased pressure Lower gas temperature Reduced pressure Volume Higher gas volume Reduced pressure Lower gas volume Increased pressure Number of particles Higher number of particles Increased pressure Lower number of particles Reduced pressure
  51. 51. 3.2 – Pascal’s Principle • He was a French physicist and mathematician. • Pascal’s Principle states that an increase in the pressure of an enclosed fluid is transmitted uniformly in all directions. • This principle applies to water pistols and hydraulic breaks!
  52. 52. • In the situation, force is transmitted from one point to another, making it possible to do work across a distance
  53. 53. • In this situation the applied force is amplified. The small downward force result in a strong upward force
  54. 54. 3.3 – Archimedes’ Principle • When dropped in a liquid, an object can float, remain suspended at a certain depth or sink. • Archimedes discovered that the volume of a solid can be determined by measuring the volume of water it displaces. • Archimedes also knew that pressure in a liquid increases as the depth increases, creating an upward force called buoyancy. • The magnitude of the buoyant force is equal to the weight of the fluid displaced by the immersed object.
  55. 55. • Archimedes’ Principle states that an object immersed in a fluid is subjected to a buoyant force equal to the weight of the fluid displaced by the object. • Air is a fluid and acts the same way but the weight of the displaced air is usually much less than the weight of the object so very few objects are suspended in the air.
  56. 56. Three possible situations: • Buoyant force (Fb) is weaker than the force of gravity (Fg) Fb<Fg - results in a downward force and the object sinks • Fb=Fg - resultant force is zero so the object maintains the same depth • Fb>Fg - resultant force is directed upward and the object rises to the surface
  57. 57. Figure 3.35 – Determining the buoyant force • The anchor has a volume of 2 L and a weight of 150 L. The volume of water displaced by the anchor is 2L. The weight of the water displaced is 20 N therefore the buoyant force is also 20 N. 20 N is less than 150 N so the anchor sinks. • Another way to think about it! • Water has a density of 1.0 g/mL. To find the density of an object use the formula p = m/V. • The anchor has a mass of the anchor is 1000o g and it has a volume of 2 L = 2000 mL. Density = 10000g/2000 mL = 5.0 g/mL • The density of the anchor is greater than the density of water so the anchor will sink.
  58. 58. Ships are designed to displace a large volume of water.
  59. 59. When the ballast tanks are filled with water, the weight of the boat increases and it sinks. To make it rise, they empty the water out of the ballast tanks. As the boat becomes lighter it rises.
  60. 60. 3.4 – Bernoulli’s Principle • Bernoulli’s Principle states that the higher the speed of a fluid, the lower its pressure, and vice versa. • This principle explains how planes fly. • The air particles travelling over the curved upper wing surface must go faster to keep up – it has to go farther . The increased speed of the particles creates lower pressure on top. The pressure on the bottom is greater, so it wants to lift the plane.
  61. 61. Making Bernoulli's Principle Fun
  62. 62. • The shower causes air displacement, inside the shower now has a lower pressure so the curtain moves in!! • The increase in the pressure do to the tilt of your hand can increase or decrease the pressure forced on the bottom of your hand is Newton's third law.