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How hard are you working

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How hard are you working

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    1. How hard are you working? How hard are you working when you carry a backpack, books or sling bag?

    3. What is Work - Section 1 Carrying a backpack may seem like work. Once you picked up the backpack by scientific definition stopped working. Work Force is exerted Object moves No work without motion object must move in the direction of the force. pushing a car stuck in the sand (No work) Pushing a car stuck in the sand and the car moves forward (work)

    4. Why is the backpack not work? Carried at a constant velocity (direction and speed) Force exerted on object is not in the direction of the motion. Exert a force upward to hold backpack however the motion is horizontal not vertical NO WORK MOTION IS NOT IN THE DIRECTION OF THE FORCE. Example: pulling a suitcase with wheels Draw a suitcase laying on the ground. Then draw the suitcase lifted at an angle. Identify the direction of force and is Work being done?

    5. Suitcase Example (Do not copy)

    6. Calculating Work (Do not copy) Which causes more work: Full backpack lifted 1 meter from the ground or an empty backpack? Lifting the full back Full backpack lifted 1 cm from the ground or the same backpack 1 meter from the ground. Full backpack 1 meter

    7. Calculating Work Work = Force X Distance Amount of force exerted (Newton) Amount of distance object is moved (meters) SI unit is N?m (newtons times meter) Example: Push a box 2 m to the right with a force of 40 N. W = 40 N X 2m W = 80 N?m

    8. Work example You move a dumbbell 6 m exerting a force of 100 N. How much work is done? W = force X distance W = 100 N X 6 m W = 600 N?m

    9. Power Power is the rate at which work is done. Carry a backpack up the stairs Weight of backpack X height of stairs Whether or not you run same work formula Power = the amount of work done on an object in a unit of time Need more power to run up the stairs because you do it in a shorter amount of time.

    10. Power continued Apply more power leads to more work (object moving in the direction of the force) Think: Is doing something faster more work? Do something faster may not be more work but would need more power Calculating Power: Power = work/time Power = force X distance / time

    11. Example Power problem A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power? Power = Force X Distance / Time Power = 11,000 N X 5 m / 25 sec. Power = 2,200 J/s

    12. Your turn You move a dumbbell 6 m exerting a force of 100 N in 30 sec. How much power is used? P = f X d/time P = 100 N X 6 m / 30 sec P = 20 J/s

    13. Power Units SI unit is joule/second (J/s) Also known as a watt (w) 1W = 1J/s Also use kilowatt equals 1,000 Watts Horsepower = 746 watts Used with engines

    14. Bellringer: Move to your groups from Friday. If you were not here on Friday join the group closest to your seat. Begin copying notes from your neighbor. Activity: Share group examples.

    15. Discovery Activity Is it a machine? Sort the following objects into those that are and those that are not machines. Select one object that you classified as a machine and explain how it functions.

    16. Objects:

    17. Answers: Machines: Non - Machines

    18. Analysis: Why did you decide certain objects were machines and others were not?

    19. What is a machine? Sect. 2

    20. Input and Ouput Input: What you do to the machine Input force force you give the machine Input distance distance the force moves a machine Output: What the machine does for you. Output force force the machine exerts on the object Output distance distance exerted on the object

    22. Input work Work = force X distance Input work = input force X input distance Output work = output force X output distance Using a machine input work = output work

    23. Machine Details Changing force: less force over a greater distance = large output force over small output distance Ramp or faucet Changing distance: more force over a shorter distance = small output force over a large output distance Chopsticks, hockey stick, bicycle in high gear Changing direction: Small input force over a large input distance = large output distance over small output force Weight machine (cable system or pulley)

    24. Mechanical Advantage

    25. Mechanical Advantage problem: A spatula has an input force of 40 N and an output force of 20 N, what is the mechanical advantage: MA = output force input force MA = 20 N 40 N MA = .5 N Is a machine with a mechanical advantage less than one beneficial? Could a machine have a mechanical advantage of one? Yes a machine who only changes direction (pulley)

    26. Efficiency Input work = output work (reality) Some work is wasted overcoming friction Efficiency = output work/ input work X % Example a machine has a 60% efficiency. Machine is losing 40% to friction or wasted energy.

    27. Efficiency Ideal machine would have what efficiency? 100% All machines have an efficiency less than 100% Ideal MA is when machine is 100% efficient Actual MA measured MA.

    28. Efficiency problem: Remember you do (input) machine does (output) The work done by a screwdriver is 10 J and the amount of work you do is 200 J. How efficienct is the screw driver? Efficiency = output work input work X 100% Efficiency = 10 J 200 J X 100% Efficiency = .2 X 100 = 20% efficient.

    29. Review: Give 2 examples of a machine What are the 3 ways a machine makes work easier. Mechanical advantage greater than one means you are increasing _______. A machine can have 100% efficiency. True or False

    30. Homework: Efficiency problems on pg. 419 Explain why a new lawnmower can only have an efficiency of 80% its ideal mechanical advantage.

    31. Simple Machines - Objective Complete foldable on simple machines. Include definition or how it works, picture or diagram and 3 real world examples of each simple machine.

    32. Simple Machines Make Foldable Six basic Simple Machines Inclined plane Screw Lever Wheel and axle pulley

    33. Inclined plane Flat sloped surface Ramp How it works: Exerts small force over a large distance Input force is less than output force MA = length of incline/ height of incline

    34. Wedge A device that is thick on one end and tapers to a thin edge. Two inclined planes Move the inclined plane itself. MA = Length of wedge/ width

    35. Screw Related to the incline plane. An inclined plane wrapped around a cylinder. As you twist a screw, the threads change the distance over which the input force is applied. MA = length around the threads/ length of the screw The closer the threads are together the greater the MA

    36. Levers A rigid bar that is free to pivot, rotate at a fixed point (fulcrum) Exert a force on one side of the fulcrum and the other side goes up with an output force. MA = Distance from fulcrum to input force/ distance from fulcrum to output force

    37. 3 Classes of levers Determined by the location of the fulcrum relative to input and output forces. 1st Class: Always change the direction of the input force.

    38. 3 classes of levers 2nd class: increase force but do not change the direction.

    39. 3 classes of levers 3rd class levers: increase distance but do not change the direction of the input force.

    40. Wheel and Axle Made of two cylindrical objects fastened together that rotate around a common axis. Larger radius = wheel Small radius = axle Exert a force on wheel which turns the axle and exerts a larger output force. increase force over a large distance.

    41. Wheel and Axle continued Riverboat: engine turns the axle which turns the wheel. Input force multiplies the distance. MA = Radius of wheel/ radius of axle

    42. Pulley Made of a grooved wheel with a rope or cable Pull on one end to lift an object at the other end Decreases input force Changes input direction Types of pulleys: Fixed pulley: attached to a structure Movable pulley: attach a pulley to the object you want to move. Block and tackle: combines fixed and movable

    43. Types of Pulleys Fixed: does not change the force but changes direction of the force (MA 1) Movable: decreases the input force but does not change the direction (MA 2) Block and tackle: (MA 3)

    44. Be inventive Your challenge is to design a machine that solves a modern day problem. Create an 8 X 11 drawing which details how your machine would work. Give your machine a name identify the problem it will solve Label all parts and identify the simple machines you are using. Color and be neat

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