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Thermal sys physics chpt10

Thermal sys physics chpt10






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    Thermal sys physics chpt10 Thermal sys physics chpt10 Presentation Transcript

    • CPO Science
      Foundations of Physics
      Chapter 9
      Unit 4, Chapter 10
    • Unit 4: Energy and Momentum
      Chapter 10 Work and Energy
      10.1 Machines and Mechanical Advantage
      10.2 Work
      10.3 Energy and Conservation of Energy
    • Chapter 10 Objectives
      Calculate the mechanical advantage for a lever or rope and pulleys.
      Calculate the work done in joules for situations involving force and distance.
      Give examples of energy and transformation of energy from one form to another.
      Calculate potential and kinetic energy.
      Apply the law of energy conservation to systems involving potential and kinetic energy.
    • Chapter 10 Vocabulary Terms
      • machine
      • energy
      • input force
      • output force
      • thermal energy
      • ramp
      • gear
      • screw
      • rope and pulleys
      • closed system
      • work
      • lever
      • friction
      • mechanical system
      • simple machine
      • potential energy
      • kinetic energy
      • radiant energy
      • nuclear energy
      • chemical energy
      • mechanical energy
      • mechanical advantage
      • joule
      • pressure
      • energy
      • conservation of energy
      • electrical energy
      • input output
      • input arm output
      • arm
      • fulcrum
    • 10.1 Machines and Mechanical Advantage
      Key Question:
      How do simple machines work?
      *Students read Section 10.1 AFTER Investigation 10.1
    • 10.1 Machines
      The ability of humans to build buildings and move mountains began with our invention of machines.
      In physics the term “simple machine” means a machine that uses only the forces directly applied and accomplishes its task with a single motion.
    • 10.1 Machines
      The best way to analyze what a machine does is to think about the machine in terms of input and output.
    • 10.1 Mechanical Advantage
      Mechanical advantage is the ratio of output force to input force.
      For a typical automotive jack the mechanical advantage is 30 or more.
      A force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)— enough to lift one corner of an automobile.
    • 10.1 Mechanical Advantage
      Output force (N)
      MA = Fo
      Input force (N)
    • 10.1 Mechanical Advantage of a Lever
      Length of input arm
      MAlever = Li
      Length of output arm
    • 10.1 Calculate position
      Where should the fulcrum of a lever be placed so one person weighing 700 N can lift the edge of a stone block with a mass of 500 kg?
      • The lever is a steel bar three meters long.
      • Assume a person can produce an input force equal to their own weight.
      • Assume that the output force of the lever must equal half the weight of the block to lift one edge.
    • 10.1 Wheels, gears, and rotating machines
      Axles and wheels provide advantages.
      Friction occurs where the wheel and axle touch or where the wheel touches a surface.
      Rolling motion creates less wearing away of material compared with two surfaces sliding over each other.
      • With gears the trade-off is made between torque and rotation speed.
      • An output gear will turn with more torque when it rotates slower than the input gear.
    • 10.1 Ramps and Screws
      Ramps reduce input force by increasing the distance over which the input force needs to act.
      A screw is a simple machine that turns rotating motion into linear motion.
      A thread wraps around a screw at an angle, like the angle of a ramp.
    • 10.2 Work
      Key Question:
      What are the consequences of multiplying forces in machines?
      *Students read Section 10.2 AFTER Investigation 10.2
    • 10.2 Work
      In physics, work has a very specific meaning.
      In physics, work represents a measurable change in a system, caused by a force.
    • 10.2 Work
      If you push a box with a force of one newton for a distance of one meter, you have done exactly one joule of work.
    • 10.2 Work (force is parallel to distance)
      Force (N)
      W = F x d
      Work (joules)
      Distance (m)
    • 10.2 Work (force at angle to distance)
      Force (N)
      W = Fd cos (q)
      Work (joules)
      Distance (m)
    • 10.2 Work done against gravity
      Mass (g)
      Height object raised (m)
      W = mgh
      Work (joules)
      Gravity (m/sec2)
    • 10.3 Why the path doesn't matter
    • 10.3 Calculate work
      A crane lifts a steel beam with a mass of 1,500 kg.
      Calculate how much work is done against gravity if the beam is lifted 50 meters in the air.
      How much time does it take to lift the beam if the motor of the crane can do 10,000 joules of work per second?
    • 10.3 Energy and Conservation of Energy
      Energy is the ability to make things change.
      A system that has energy has the ability to do work.
      Energy is measured in the same units as work because energy is transferred during the action of work.
    • 10.3 Forms of Energy
      Mechanical energy is the energy possessed by an object due to its motion or its position.
      Radiant energy includes light, microwaves, radio waves, x-rays, and other forms of electromagnetic waves.
      Nuclear energy is released when heavy atoms in matter are split up or light atoms are put together.
      The electrical energy we use is derived from other sources of energy.
    • 10.3 Potential Energy
      Mass (kg)
      Ep = mgh
      Potential Energy
      Height (m)
      of gravity (m/sec2)
    • 10.3 Potential Energy
      A cart with a mass of 102 kg is pushed up a ramp.
      The top of the ramp is 4 meters higher than the bottom.
      How much potential energy is gained by the cart?
      If an average student can do 50 joules of work each second, how much time does it take to get up the ramp?
    • 10.3 Kinetic Energy
      Energy of motion is called kinetic energy.
      The kinetic energy of a moving object depends on two things: mass and speed.
      Kinetic energy is proportional to mass.
    • 10.3 Kinetic Energy
      Mathematically, kinetic energy increases as the square of speed.
      If the speed of an object doubles, its kinetic energy increases four times. (mass is constant)
    • 10.3 Kinetic Energy
      Mass (kg)
      Speed (m/sec)
      Ek = 1 mv2
      Kinetic Energy
    • 10.3 Kinetic Energy
      Kinetic energy becomes important in calculating braking distance.
    • 10.3 Calculate Kinetic Energy
      A car with a mass of 1,300 kg is going straight ahead at a speed of 30 m/sec (67 mph).
      The brakes can supply a force of 9,500 N.
      a) The kinetic energy of the car.
      b) The distance it takes to stop.
    • 10.3 Law of Conservation of Energy
      As energy takes different forms and changes things by doing work, nature keeps perfect track of the total.
      No new energy is created and no existing energy is destroyed.
    • 10.3 Energy and Conservation of Energy
      Key Question:
      How is motion on a track related to energy?
      *Students read Section 10.3 BEFORE Investigation 10.3
    • Application: Hydroelectric Power