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Bell Ringer 3-2-10

Bell Ringer 3-2-10. What is the formula for work? What are the units for work? If I pull a rope towards me but it doesn’t move, is that considered work? Work includes force and motion in the _______ direction. Chapter 12 Section 2 How Machines Do Work.

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Bell Ringer 3-2-10

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  1. Bell Ringer 3-2-10 • What is the formula for work? • What are the units for work? • If I pull a rope towards me but it doesn’t move, is that considered work? • Work includes force and motion in the _______ direction.

  2. Chapter 12 Section 2How Machines Do Work

  3. Machines are devices that make it easier to do work. • Machines change the way a person does work, not the amount of work that needs to be done.

  4. How do Machines make work Easier? • By changing the amount of force you exert • By changing the distance over which you exert the force • By changing the direction in which you exert the force.

  5. Input force is the force you exert on a machine. • The input force moves the machine a certain distance, called the input distance. • Input Force x Input Distance = Input Work

  6. Output force is the force a machine puts on an object. • The output distance is the distance over which the machine exerts the force. • Output force x Output Distance = Output Work

  7. Mechanical advantage is the number of times a machine increases a force exerted on it. • Mechanical advantage = Output force Input force

  8. Some machines make work easier by allowing you to exert a smaller force over a longer distance. • Other machines allow you to exert your force over a shorter distance. • Other machines allow you to change the direction of input force

  9. Efficiency is the ability to convert input work to output work, calculated as: • Efficiency = output work x 100% input work . • Oil, or another lubricant, can increase efficiency.

  10. Friction reduces efficiency by converting some work into heat. • The efficiency of a real machine is always less than 100 percent because of friction.

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