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Understanding Work, Energy, and Simple Machines: Concepts and Applications

This chapter explores fundamental concepts in physics, focusing on work and machines. It defines work as the product of force and distance, measured in joules. The distinction between kinetic and potential energy, along with various forms of energy, is discussed. The chapter introduces simple machines, emphasizing levers and their three classes, mechanical advantage, and efficiency concerns. It explains how machines can alter force direction and magnify effort, incorporating examples of pulleys, inclined planes, screws, wedges, and the wheel and axle.

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Understanding Work, Energy, and Simple Machines: Concepts and Applications

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  1. Chapter 8 Work and Machines

  2. Lesson 1: Work • Work  when something moves because of a force being applied • Work = force x distance • Label is newton-meter or joule

  3. Work formula w f d

  4. Lesson 2: Energy • Energy ability to do work • There are 2 kinds of energy • Kinetic energy in motion • KE = ½ mv² • Potential stored energy • PE = mgh • gravity = 9.8 m/s²

  5. 6 Forms of Energy • Chemical energy  stored in the bonds btw. atoms • Heat energy  moving particles in matter • Mechanical energy  in moving objects

  6. 6 Forms of Energy cont. • Nuclear energy  stored in the nucleus of atoms • Radiant energy  light energy • Electrical energy  causes electrons to move

  7. Energy can be converted from one form to another • Generator device used to convert mechanical energy to electrical energy • Law of conservation of energy energy cannot be created nor destroyed

  8. Lesson 3: Levers • Simple machines tool that makes it easier or possible to do work • Lever bar that is free to turn around a fixed point • Fulcrum fixed point around a lever turns

  9. Levers cont. • Effort force (FE force applied to a machine by the user • Resistance force (FR) force applied to the machine by the object to be moved

  10. 3 Classes of Levers • Based on the position of the resistance, fulcrum, & effort • First-class lever fulcrum is btw effort & resistance • Changes direction of force & can increase force

  11. Examples of class 1 levers include: • Teeter-totter • Scissors • Pair of pliers

  12. Second-class lever resistance is btw effort and fulcrum • Always increases force • Do not change direction

  13. Examples of class 2 levers include: • Wheelbarrow • Crowbar • Nut cracker

  14. Third-class levers effort is btw resistance & fulcrum • Increases distance which cause resistance to move further or faster

  15. Examples of class 3 levers include: • Tweezers • Stapler • Mousetrap • Broom • Hockey stick

  16. Efficiency • A simple machine cannot do more work than the person using it • Machines increase or change the direction of force • If less effort is needed, more distance is needed also

  17. Effort distance & resistance distance • Effort distance (dE) the distance the effort moves • Resistance distance (dR) the distance the resistance moves • Effort distance is greater than resistance distance

  18. Work Input & Work Output • Work input work put into a machine by the user • Work input = FE x dE • Work output work done by a machine against the resistance • Work output = FR x dR

  19. Efficiency • Efficiency = work output work input x 100 FR x dR FE x dE x 100

  20. Lesson 4: Mechanical advantage • Mechanical advantage number of times a machine multiplies its effort force • Mechanical advantage = resistance force effort force • MA = FRFE

  21. Effort Arm & Resistance Arm • Effort arm distance btw the fulcrum & effort force • Resistance arm distance btw the fulcrum & resistance force • MA = effort arm resistance arm

  22. Lesson 5: Other simple machines • Pulley wheel w/ a rope, chain, or belt around it • A single pulley changes direction, not force; ma = 1 • Fixed pulley attached at top • Movable pulley entire pulley & object attached will rise

  23. Pulley cont. • MA of a pulley = number of ropes that pull upward • The easier to lift an object, the more distance you pull on the rope

  24. Inclined Plane • Inclined plane made of a ramp used to lift an object • MA = length of ramp height of ramp • Gradual slant = greater MA, but greater distance • Steeper slant = less MA, but shorter distance

  25. Screw • Screw inclined plane wrapped around a nail • MA depends on distance btw threads • Smaller distance = more MA

  26. Wedge • Wedge 2 inclined planes placed back to back; inclined plane that moves when used • Thick at one end, thinner at the other • Thinner, more gradual wedge = greater MA

  27. Wheel & Axle • Wheel & axle wheel attached to a shaft • Increases the force you apply to the wheel • MA depends on the size of the wheel & thickness of axle

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