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4.2 and 4.3: Simple Machines

4.2 and 4.3: Simple Machines. pp. 91 - 103 Mr. Richter. Agenda. Warm – Up Welcome Back/Plan for the rest of the year Intro to Simple Machines Notes Today: Machines Mechanical Advantage Efficiency. Tomorrow: Types of simple machines. Objectives: We Will Be Able To….

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4.2 and 4.3: Simple Machines

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  1. 4.2 and 4.3: Simple Machines pp. 91 - 103 Mr. Richter

  2. Agenda • Warm – Up • Welcome Back/Plan for the rest of the year • Intro to Simple Machines • Notes Today: • Machines • Mechanical Advantage • Efficiency • Tomorrow: • Types of simple machines

  3. Objectives: We Will Be Able To… • Describe how a machine works in terms of input and output. • Define some simple machines and name some examples. • Calculate the mechanical advantage of a simple machine given the input and output force. • Calculate the efficiency of a simple machine.

  4. Warm-Up: • What is a machine? Why do we use them?

  5. Machines

  6. Machines • Humans are amazing creatures, and we are able to do many things. • But there are some things we cannot accomplish on our own. • A machine is a device with moving parts that work together to accomplish a task.

  7. Machines • A simple machine is a device that accomplishes a task with only one movement.

  8. Machines • Every machine, simple or complicated, has an input or output. • The input is how much force, work, power or energy is used to make the machine work. • What do you do for it? • The output is how much force, work, power or energy the machine produces. • What does it do for you?

  9. Machines

  10. Mechanical Advantage and Efficiency

  11. Mechanical Advantage • Machines are measured by two standards: mechanical advantage and efficiency. • Mechanical advantage tells you how much the machine helps you. • Mechanical advantage is the ratio of the output force to the input force.

  12. Mechanical Advantage • A large mechanical advantage means you need to put in a very small amount of force to get a large force out. • A small mechanical advantage means the opposite. • MA is unit-less.

  13. Mechanical Advantage • What is the mechanical advantage of a lever that allows Jorge to lift a 24 N box with a force of 4 N? • 6

  14. Efficiency • Efficiency is a measure of how close to perfect a machine is. • Efficiency measures how much energy is conserved, and how much is lost to friction. • The efficiency of a machine is the ratio of the output work to the input work. Expressed as a percent. (%)

  15. Efficiency • An excellent machine is about 95% efficient. • This means only 5% of the energy is wasted due to friction. • No machine is 100% efficient. • Yet?

  16. Efficiency • A person does 8000 J of work to pedal a bicycle. The bicycle outputs 6000J of energy. How efficient is the bicycle? • 75%

  17. Homework • pp. 107 – 108 Solving Problems • #8-10, 18-20

  18. Warm Up • If the weight at the bottom of the pulley system weighs 100 N, how much force does the man have to use to lift the weight?

  19. Pulleys

  20. Pulleys • In an ideal (perfect) machine, the input work is equal to the output work. • When we analyze simple machines, we will assume they are ideal unless otherwise noted.

  21. Pulleys • In a pulley system, the mechanical advantage is determined by the number of ropes pulling up on the load at the same time.

  22. Pulleys • The MA of each pulley system is equal to the number of ropes pulling upward on the load.

  23. Pulleys Homework • Worksheet Problems 1 and 3 as a class. • Then the rest of the worksheet on your own.

  24. Warm-Up • Where do you see levers used in real life?

  25. Levers

  26. Levers • “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” • - Archimedes

  27. Levers • A lever is a rigid structure that rotates around a fixed point. • The fixed point is called a fulcrum. • The side of the lever where the input force is applied is called the input arm. • The output arm applies the output force.

  28. Levers • The mechanical advantage of a lever is the ratio of the length of its input arm to the length of its output arm.

  29. Three Classes of Levers • Levers can be sorted into three separate classes. • First class levers’ input and out put arms are on opposite sides of the fulcrum. • Examples: • see-saw • crowbar

  30. Three Classes of Levers • Second class levers have the input and output force on the same side of the fulcrum, but the input force is farther from the fulcrum. • Example: • Wheelbarrow

  31. Three Classes of Levers • Third class levers also have the input and output forces on the same side of the fulcrum, but the input force is closer to the fulcrum. • This means the input force is greater(!) than the output force. • Used for moving objects large distances. • Example: • biceps

  32. Levers • A lever has a mechanical advantage of 4. Its input arm is 60 cm long. • How long is its output arm? • If the lever is used to lift an object that weighs 20 N, how much force is required?

  33. Wrap-Up: Did we meet our objectives? • Describe how a machine works in terms of input and output. • Define some simple machines and name some examples. • Calculate the mechanical advantage of a simple machine given the input and output force. • Calculate the efficiency of a simple machine.

  34. Homework • Finish Lever Worksheet

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