Work And Power
- 2. What is Work?Students will be able toCalculate work and powerExplain how machines workCalculate mechanical advantageCalculate machine efficiencyPage 108
- 3. The Meaning of WorkWork is done on an object…If the object moves in same direction in which the force is exertedKEYS The object must be in motion! Force must be in the direction of motion108
- 4. The Meaning of Work108
- 5. The Meaning of WorkIn order for you to do work you must move the object some distance.When you pull a suitcase with wheels, why does only part of your force do work?Only force in the direction of motion is work
- 6. Brief DemonstrationOne person lift textbook off groundAnother hold textbookWhich one is exerting force?Which one is working?
- 7. Calculating WorkThe formula for work is…Work = Force x distanceForce is measured in NewtonsDistance is measured in metersSI unit = joule1 N x 1 m = joule
- 8. Question?Which would be more work?A. Lifting a full backpack 1 cm off the ground B. Lifting an empty backpack 1 meter off the ground
- 9. Calculating WorkYou want to move a plant from the floor to a table 0.5 meters off the ground.How much work is done on a 100 N plantW = F x DW = 100 N x 0.5 mW = 50 N mW = 50 J108
- 10. Calculating WorkHow much work is done on a 50 N plantW = F x DW = 50 N x 0.5 mW = 25 N mW = 25 J108
- 11. PowerWork is not affect by time So it is the same amount of work if you walk or run up the same stairs.*The only thing that matters is force and distance!POWERThe amount of work done in a unit of timeSo you need more power to run upstairs than walkPower = Work / TimePower = Force x Distance / Time
- 12. Power UnitsPower = Work / timePower = J / SecPower = Watt1000 Watts = kilowatt
- 13. CalculationA 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 of the tow truck?Force = 11,000 NDistance = 5 mTime = 25 secondsPower = Force x distance / timePower = 11,000 x 5 m / 25 secPower = 2,200 W or 2.2 kW112
- 14. U.S. Power UnitEngines are rated by a unique power unit Called horsepower 1 horsepower = 746 watts113
- 15. Understanding Main IdeasHow can you determine work is being done on a box?Is the box moving? Must be moving to be doing work.Formula for workWork = Force x DistanceWhat work is done for a 40 N object moved 2 metersWork = 40 N x 2 mWork = 80 J