Objectives: • Define work • Calculate work done on an object and the rate at which work is done • Use ‘work’ as a science term
Work and Power notes: • In science, ‘work’ has a specific meaning • Work is ONLY done when a force causes a change in the position or motion of an object in the direction of the applied force • i. e. making something move because of force
Work or no work?
Work or no work? Lifting a barbell over your head?
Work or no work? Holding a barbell over your head?
Work or no work? Is there work being done ON the tray?
THINK! • What’s the difference between doing work and not doing work (in a scientific sense)? • How do you think you might need to know in order to calculate ‘work’? (Hint: what HAS to happen for work to be done? )
• If to do work you must apply force that changes the position of an object, in the direction of an applied force… • Think back: what is “The change of position in a direction”? Displacement
WORK EQUATION: • Work = Force x displacement • Work Equation W = work, F = force, Δx = displacement W = FΔx
• Work is measured in joules (J). – 1 J = 1 N • m = 1 kg • m 2/s 2 – 1 joule is roughly equal to the energy required to lift a small apple 1 meter *N measures force/weight *m measures mass. . . To find weight in N, need to use Fg=mg James Prescott Joule
THINK! • At what point in this clip is work being done? Why?
Practice: • A crane uses an average force of 5200 N to lift a crate 25 m. How much work does the crane do on the crate?
• An apple weighing 1 N falls a distance of 1 m. How much work is done on the apple by the force of gravity?
Challenge! • A mechanic uses a hydraulic lift to raise a 1200 kg car 0. 5 m off the ground. How much work does the lift do on the car?
Exit Ticket #45 -48
45. What is the equation to find work? a. W=N Δx b. W=FΔx c. W=N/Δx d. W=F/Δx
46. The brakes on a bicycle apply 125 N of frictional force to the wheels as the bicycle travels 14. 0 m. How much work have the brakes done on the bicycle? a. 8. 9 J b. 0. 112 N c. 1750 J d. 1750 N
47. What is displacement? a. b. c. d. The distance an object travels The direction an object travels The change of position in a direction None of the above
48. Anna walks down the hall on her way to class. She weighs 565 N and carries a backpack that weighs 63. 2 N. Calculate the work she does on the backpack if she walks 35. 2 m to class. a. 19888 J b. 2224. 64 J c. 1. 80 J d. 0 J