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# Chapter 14 work and power power point kremkus

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Mrs. Kremkus ch 14 PowerPoint

Mrs. Kremkus ch 14 PowerPoint

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• 1. CHAPTER 14Work, Power and Machines
• 2. 14.1 Work and Power&#x2022; Work requires motion .&#x2022; Work is the product of force and distance.&#x2022; Figure 1 work is only being done when the weight lifter is lifting the barbell.&#x2022; Therefore work requires motion&#x2022; For a force to do work on an object some of the force must act in the same direction as the object moves. No movement, No work is done.
• 3. 14.1 Work and Power&#x2022; Work depends on direction.&#x2022; Amount of work done on an object depends on the direction of the force and the direction of the movement.&#x2022; A force does not have to act entirely in the direction of movement to do work.&#x2022;
• 4. 14.1 Work&#x2022; Suitcase ex p. 413&#x2022; Pulling a suitcase the force acts upward and to the right along the handle&#x2022; The suitcase moves only to the right along ground.&#x2022; Horizontal portion of the force acting in the direction of motion&#x2022; Only the horizontal part of the applied force the part in the direction of movement does work&#x2022; Any part of a force that does not act in the direction of motion does no work on an object.
• 5. Calculating Work&#x2022; Work = Force x Distance&#x2022;W = F &#xD7; D&#x2022; Units= Joule (J) Is the SI Unit of work&#x2022; Force =Newtons (N)&#x2022; Distance = meters (m)&#x2022; Newton &#x2013; meters = Joules
• 6. Calculating work sample problemA body builder lifts a 1600 N barbellover his head and is lifted to a height of2.0 meters. How much work has hedone?W=F&#xD7;DW=1600N &#xD7; 2mW= 3200N&#xB7;m=3200J
• 7. 14.1 What is Power?&#x2022; Power- is the rate of doing work. The amount of work done in a certain amount of time.&#x2022; Need to use more power to do work at a faster rate.&#x2022; To increase power you can increase the amount of work done in a given time or you can do a given amount of work in less time.
• 8. 14.1 Power&#x2022; Calculate Power&#x2022; Formula: Power = Work p= w&#x2022; time t&#x2022;&#x2022; SI Units= Watts (W) = 1 J/S&#x2022; Horsepower (hp) another common unit&#x2022; 1 hp = 746 watts&#x2022; Power = Watts [W]&#x2022; Work = Joules [J]&#x2022; Time = Seconds [s]&#x2022; Distance= Meters [m]
• 9. 14.1 Power&#x2022; Sample Problems:&#x2022; 1. How much power does a light bulb contain if it does 600J of work in 5 Seconds?&#x2022; P= W Solving for Power. P = 600J = 120 W = 100 W &#x2022; t 5s sig. figs&#x2022; 2. If a car has 700W of power and does 2000J of work. How much time was involved?&#x2022; Solving for time. t = W Changed the power formula&#x2022; P&#x2022; t = 2000J = 2. 86 s = 3 s with sig. figs&#x2022; 700W
• 10. 14.2 Work and Machines&#x2022; Machine &#x2013; A device that changes a force.&#x2022; Machines make work easier to do&#x2022; -change the size of a force needed&#x2022; -the direction of a force&#x2022; -or the distance over which a force acts.
• 11. 14.2 Work and Machines&#x2022; 1. Increasing Force&#x2022; Example: Jack handle&#x2022; A small force exerted over a large distance becomes a large force exerted over a small distance.&#x2022; However, if a machine increases the distance over which you exert a force, then it decreases the amount of force you need to exert.
• 12. 14.2 Work and Machines&#x2022; 2. Increasing Distance&#x2022; Example: oars&#x2022; - decreases the applied force, but increases the distance over which the force is exerted.&#x2022; - However, a machine that decreases the distance through which you exert the force increases the amount of force required.
• 13. 14.2 Work and Machines&#x2022; 3. Changing Direction&#x2022; Some machines change the direction of the applied force&#x2022; Pulling on an oar &#x2013; other ends moves opposite
• 14. 14.2 Work and Machines&#x2022; Work input and work output&#x2022; -because of friction, the work done by a machine is always less than the work done on the machine.&#x2022; Work input of a machine&#x2022; Input force &#x2013; force you exert on a machine.&#x2022; Input distance &#x2013; the distance the input force acts through.
• 15. 14.2 Work and Machines&#x2022; Work Input &#x2013; the work done by the input force acting through the input distance&#x2022; Work input= input force &#xD7; input distance&#x2022; Explain perpetual motion page 419 (read on own )
• 16. 14.2 Work and Machnes&#x2022; Work output of a machine&#x2022; Work output force the force exerted by a machine.&#x2022; Output distance &#x2013; the distance the output force is exerted through&#x2022; Work output- the output force multiplied by the output distance.&#x2022; Remember you cannot get more work out of a machine than you put in it.
• 17. 14.2 Work and Machines&#x2022; Explain movement of oar through the water.&#x2022; Newton&#x2019;s 3rd Law&#x2022; -fluid friction slows its motion.&#x2022; Output work is always less than input work due to friction.
• 18. 14.3 Mechanical Advantage andEfficiency&#x2022; The mechanical advantage of a machine is the number of times that the machine increases an input force.&#x2022; The actual mechanical advantage (AMA)- is the mechanical advantage determined by measuring the actual forces acting on a machine.&#x2022; AMA = the ratio of the output force to the input force.
• 19. 14.3 Mechanical Advantage and Efficiency&#x2022; AMA= output force&#x2022; input force&#x2022; Sample Problem:&#x2022; If you exert 100N on a jack to lift a 10,000N car, what would be the jack&#x2019;s AMA? (do on board)
• 20. 14.3 Mechanical Advantage and Efficiency&#x2022; Ideal Mechanical Advantage &#x2013; of a machine is the mechanical advantage in the absence of friction.&#x2022; To increase the mechanical advantage of a machine you would reduce the friction.&#x2022; This would allow the mechanical advantage of a machine be at its maximum possible value.&#x2022; However, friction is always present and this is why the AMA of a machine is always less than the IMA.
• 21. Calculating the ideal mechanical advantage&#x2022; It is easier to calculate the actual mechanical advantage because it depends only on the locations of the forces and the distances they act on.&#x2022; IMA = Input distance&#x2022; Output distance&#x2022; Sample Problem:&#x2022; What is the IMA of a 5m long ramp that rises 1m off the ground at its end? (answer on board)&#x2022; If the input distance is greater than the output distance the IMA has to be greater than 1.
• 22. 14.3 Efficiency&#x2022; Efficiency of a machine is the percentage of the work input that becomes work output.&#x2022; Will always be less than 100% because of friction.&#x2022; Formula:&#x2022; Efficiency = Work output &#xD7;100&#x2022; Work input&#x2022; Sample Problem: What is the efficiency of a machine that has a work input of 40J and a work output of 35J? (answer on board)
• 23. 14.4 Simple Machines&#x2022; Machines (mechanical devices) are combinations of 2 or more of the 6 different simple machines.&#x2022; The 6 types of simple machines are:&#x2022; 1. the lever 2. the wheel and axle&#x2022; 3. the inclined plane&#x2022; 4. the wedge 5. the screw&#x2022; 6. the pulley
• 24. 14.4 Simple Machines&#x2022; 1. The Lever&#x2022; A rigid bar that is free to move around a fixed point.&#x2022; The fulcrum- is the fixed point the bar rotates around.&#x2022; There are 3 classes of levers based on the locations of the input force, the output force, and the fulcrum.
• 25. 14.4 Simple Machines- Levers&#x2022; Input arm of a lever is the distance between the input force and the fulcrum.&#x2022; Output arm of a lever is the distance between the output force and the fulcrum.&#x2022; You can calculate the IMA for a lever by dividing the input arm by the output arm.
• 26. 14.3 Simple machines - Levers&#x2022; 3 Types of Levers&#x2022; 1. 1st Class Lever- identified by the position of the fulcrum.&#x2022; The fulcrum is always located between the input force and the output force.&#x2022; The mechanical advantage can be greater than 1, equal to 1, or less than 1 depending on the location of the fulcrum.&#x2022; Ex: Screwdriver, seesaw, scissors
• 27. 14.4 Simple Machines-Levers&#x2022; 2nd Class Levers-&#x2022; Output force is located between the input force and the fulcrum&#x2022; The mechanical advantage is always greater than 1.&#x2022; Ex: Wheel barrow&#x2022; Handle is the input force, wheel is the fulcrum, and the load lifted is the output force.
• 28. 14.3 Simple Machines- Levers&#x2022; 3rd Class Levers-&#x2022; The input force is located between the fulcrum and the output force.&#x2022; The output distance over which it exerts its force is always longer than the input distance you move the lever through.&#x2022; The mech. Advantage is less than 1.&#x2022; Ex: baseball bat, hockey stick, golf club, broom, rake
• 29. 14.3 Simple Machines&#x2022; Wheel and Axle&#x2022; Consists of two discs or cylinders, each one with a different radius.&#x2022; Input force can be exerted on the wheel or axle depending on the machine.&#x2022; Calculate IMA- divide the radius where the input force is exerted by the radius where the output force is exerted.&#x2022; Mech. Adv. can be greater or less than 1.
• 30. 14.3 Simple Machines&#x2022; Inclined Planes&#x2022; A slanted surface along which a force moves an object to a different elevation.&#x2022; Distance along ramp is the input distance.&#x2022; The height of the ramp is the output distance.&#x2022; IMA is the distance along the inclined plane divided by its change in height.
• 31. 14.3 Simple Machines&#x2022; Wedges and Screws&#x2022; Like inclined planes because they have a sloping surface but wedges and screws move.&#x2022; Wedges- used to raise an object or split an object apart.&#x2022; A v-shaped object whose sides are two inclined planes sloped toward each other.&#x2022; Mech. Adv. is greater than 1.
• 32. 14.3 Simple Machine&#x2022; Thinner wedges have a greater IMA than athick wedge as long as their widths are thesame.&#x2022; Screws&#x2022; An inclined plane wrapped around a cylinder.&#x2022; Screws with threads that are closer together have a greater IMA.
• 33. 14.3 Simple Machines&#x2022; Pulleys- pull with less force than is needed to lift the load upward.&#x2022; A simple machine that consists of a rope that fits into a groove in a wheel.&#x2022; They produce an output force that is different in size, direction, or both, from that of the input force.&#x2022; The IMA of a pulley or pulley system is equal to the number of rope sections supporting the load being lifted.
• 34. 14.3 Simple Machines&#x2022; Fixed Pulleys- is a wheel attached in a fixed location.&#x2022; It is only able to rotate in place.&#x2022; Direction of the force is changed, but the size of the force isn&#x2019;t.&#x2022; IMA is 1. The input and output force are about the same.&#x2022; Examples: Flagpole, blinds
• 35. 14.3 Simple Machines&#x2022; Moveable Pulley- A pulley is attached to the object being moved not to a fixed location.&#x2022; It reduces the input force needed to lift a heavy object.&#x2022; Examples: sails, platforms (window washing).&#x2022; Pulley system- combining fixed and moveable pulleys.&#x2022; Large mech. Adv., depends on how the pulleys are arranged.
• 36. 14.3 Simple Machines&#x2022; Compound Machine- A combination of 2 or more simple machines that operate together.