Chapter 8-- Work and Simple Machines Material on Final Exam

1. Chapter 8-- Work and Simple MachinesMaterial on Final Exam

2. Section 8.1 Objectives • Determine when work is being done on an object. • Calculate the amount of work done on an object. • Calculate the amount of power needed to perform a certain task. • Explain the difference between work and power. • Terms to Learn: • Work, Joule, Power and Watt

3. Work • **Recall that an object begins moving only when an ____________________________acts on it.* • _______ is the product of _______ and __________. • _______ is done when an object __________ in the _________________________ of the _________. • 2 things must happen for work to be done. • The object ____________________. • The object must move in the _____________________as the ___________________.

4. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class? ___________ • a mouse pushing a piece of cheese with its nose across the floor? _________

6. Work or Not? • Ex: If a student pushes a wall with all of his strength? • A student carrying a book?

7. Work ______ = ______ x __________ W = F x d • SI unit for Force = __________ • SI unit for Distance = _______ • SI unit for Work = ________ • Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

8. Same work, different force

9. Power- How fast work is done! • ________ is the ______ at which __________. • Doing work at a higher rate requires more Power. To _______________, you can _____________ the amount of ____________ done in a given time, or you can do a given amount of work in less time. • OR Force x Distance Time • SI unit for power = __________ • SI unit for work = ___________ • SI unit for time = ___________

10. Math Practice • If it takes you 10 seconds to do 150 joules of work on a box to move it up a ramp, what is your power output? • A light bulb is on for 12 s, and during that time it uses 1,200 J of electrical energy. What is the wattage (power) of the light bulb?

11. Check for Understanding 1.Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Explain your answers. Which student does the most work? Which student delivers the most power?

12. 2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s2 a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Work=Force x Distance Power = Work/Time

13. Section 8.1 Objectives Please answer these on your objective sheet • Determine when work is being done on an object. • Calculate the amount of work done on an object. • Calculate the amount of power needed to perform a certain task. • Explain the difference between work and power.

14. Section 8.2 Objectives • Explain how a machine makes work easier. • Describe and give examples of the force-distance trade off that occurs when a machine is used. • What is the formula to calculate mechanical advantage. • What is the formula to calculate mechanical efficiency. • Explain why machines are not 100% efficient. • Terms to learn • Machine, work input, work output, mechanical advantage, mechanical efficiency

15. Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

16. Simple Machines • A ____________ is a device that helps make ____________________ to perform by accomplishing one or more of the following functions: • _____________ a _______ from one place to another, • _____________ the _____________ of a force, • _____________ the _____________ of a force, • _____________ the _____________ or _______ of a force.

17. Mechanical Advantage • It is useful to think about a machine in terms of the _____________ (the force _________) and the ____________ (force from the ______________ to perform a task). • When a ____________ takes a small input force and _____________ the amount of the _____________, a ______________________ has been produced.

19. Mechanical Advantage • The ______________________is the ____________ of times the machine ____________ or _____________ an_________________. • Mechanical Advantage = Output Force Input Force • The ideal mechanical advantage is the advantage in the absence of friction. • Never happens because all objects experience friction.

20. Mechanical Efficiency • ____________________________ – the percentage of work input that becomes work output. • Can never be 100% due to_____________ ME = Work Output x 100 Work Input

21. Section 8.2 Objectives Please answer the following on your objective sheet • Explain how a machine makes work easier. • Describe and give examples of the force-distance trade off that occurs when a machine is used. • What is the formula to calculate mechanical advantage. • What is the formula to calculate mechanical efficiency. • Explain why machines are not 100% efficient.

22. Section 8.3 Objectives • Identify and give examples of the six types of simple machines. • Analyze the mechanical advantage provided by each simple machine. • Identify the simple machines that make up a compound machine. • Terms to learn: • Lever, pulley, wheel and axle, inclined plane, wedge, screw and compound machine.

23. Simple Machines The six simple machines are: 1. Lever 2. Wheel and Axle 3. Pulley 4. Inclined Plane 5. Wedge 6. Screw

24. The Lever • A __________ is a ________ that rotates around a fixed point called the fulcrum. • __________ – a __________ • The bar may be either straight or curved. • In use, a lever has both an effort (or applied) force and a load (resistant force).

25. First Class Lever I = input force or effort O = output force/ weight F = Fulcrum • 1st Class – fulcrum is between the ____________ and _______________ • Examples: See-saw, scissors, tongs. TIP: A ___irst class lever has the ___ulcrum in the center!

26. Second Class Lever I = input force or effort O = output force/ weight F = Fulcrum • 2nd Class –____________ located ____________ the _______________ and ________________. • Example: Wheelbarrow, bottle opener, nutcracker, crowbar TIP: A Sec___nd class lever has the ___utput in the center!

27. Third Class Lever I = input force or effort O = output force/ weight F = Fulcrum • 3rd Class – ___________ is ____________ the _____________ and ________________. • Provide a ____________ _____________ that is always ______________. • Examples: Hockey stick, golf club, screwdriver opening paint can, broom, tweezers, hammer, stapler TIP: A Th___rd class lever has the ___nput in the center!

28. Wheel and Axle • The __________________ is a simple machine consisting of a __________ rigidly secured to a _______________ or shaft, called an axle. • When either the wheel or axle turns, the other part also turns. • One full revolution of either part causes one full revolution of the other part.

29. Inclined Plane • An _________________is a _____________along which a force moves an object/ weight from a lower to higher elevation. • _________ make lifting a heavy object easier because _____________is needed to move the object over a ___________________.

30. Wedges and Screws • A ____________ is a ____________ object whose sides are two _________________sloped towards each other. • A ____________ is an _______________ wrapped around a cylinder.

31. Pulley • A__________is a simple machine that consists of a _________ that fits into a _________ in a ________. • The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

32. More than One • Compound Machines are a _________________ of ________ or ____________________________that operate together.

33. Section 8.3 Objectives Please answer these on your objectives sheet • Identify and give examples of the six types of simple machines. • Analyze the mechanical advantage provided by each simple machine. • Identify the simple machines that make up a compound machine.