Name ________________________________Physical Science Date _______________Period ________Mrs....
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Name ________________________________ Physical Science Date _______________ Period ________ Mrs. Haentges Notes for Chapter 6 – Work and Machines Work - _____energy transferred when forces make something move___ In order for work to be done, something must ____move____ Formula for work: Work = ______force______ x _____distance_____ W = f d Unit for work ____Joule____________
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Transcript of Name ________________________________Physical Science Date _______________Period ________Mrs....
Name ________________________________ Physical Science Date _______________ Period ________ Mrs. Haentges Notes for Chapter 6 – Work and Machines
Work - _____energy transferred when forces make something move______ In order for work to be done, something must ____move____ Formula for work:
Work = ______force______ x _____distance_____
W = f d
Unit for work ____Joule____________
Example #1:A force of 75 N is used to move a couch 3 m. How much work is done in moving the couch?
W = f●d
W = 75 N ● 3 m
W = 225 JExample #2:
A lawn mower is pushed with a force of 80 N. If 12,000 J of work is done in mowing a lawn, what is the total distance the lawn mower was pushed?
d = W/f
d = 12,000 J/80 N
d = 150 m
Power - __amount of work done in a second__(rate at which work is done)__ Formula for power:
Power = work P = w (f●d) time t t
(sometimes you will need to calculate work first)
Unit for power ______watt_______ Example #1:
A runner performs 1300 J of work in 10 seconds. What is the runner’s power? P = w/t
P = 1300J/10 s
P = 130 W
How could the runner be more powerful? _____run faster______
Machine - _____device that makes doing work easier_________ Three ways that machines make work easier: ● increasing force applied to the object ● increasing the distance over which the force is applied ● changing the direction of the force Input force - ____force applied TO the machine________ Example of input force - ____pulling down on a crowbar______ Output force - _____force applied BY the machine_______ Example of output force - ___crowbar lifting up a lid_____ Ideal Machine - ____has no friction___(work in = work out)___
Mechanical Advantage - ____the ratio of output force to_______ ___input force__(how many times easier it is to use the machine)__ Formula for mechanical advantage:
Mechanical advantage = output force input force
MA = Fout
Fin
Mechanical advantage does not have a label.
Example #1:A worker applies an input force of 20 N to pry open a window that has an output force of 500 N. What is the mechanical advantage of the crowbar?
MA = Fout/Fin
MA = 500 N/20 N MA = 25Example #2:
Find the input force needed to lift a 200 N rock, using a jack with a mechanical advantage of 10.
Fin = Fout/MA
Fin = 200 N/10
Fin = 20 N
Efficiency - __how much work put into a machine is____________ ____changed to useful work put out by a machine_____________
The Wout of a machine is less than the Win because of __friction___Therefore, machines are always less than 100% efficient.How do you increase the efficiency of a machine?
decrease the friction
Simple Machine - ____does work with only one movement_________ Examples of simple machines - ______________________________ _______________________________________________________ Six types of simple machines 1. Levers 2. Pulleys 3. Wheel and Axle (gear) 4. Inclined Plane 5. Screw 6. Wedge
1. Levers - _bar that is free to pivot around a fixed point_________
Parts: fulcrum - ___fixed point of a lever_______________
Input arm - __where the input force is applied______
Output arm - __where the output force is applied____ 1st class lever – fulcrum is located between the input and output forces
example – seesaw, screwdriver opening a can O I Δ-F
2nd class lever – output force is located between the input force and the fulcrumexample - wheelbarrow
O I Δ-F
3rd class lever – input force is located between the output force and the fulcrum
example – baseball bat, rake O I___________ Δ-F
IMA of a lever = length of input arm or Lin
length of output arm Lout
2. Pulleys - ___grooved wheel with a rope running along the groove____
Example: on a flagpole or a crane
Pulleys work like ____first class levers______________________
The IMA of a single fixed pulley is ____1____ Block and tackle – ____system of pulleys_______ More pulleys give greater mechanical advantage – less effort.
The IMA of a block and tackle = ____number of pulleys_____
3. Wheel and Axle - __an axle attached to the center of a ______
____wheel – the wheel and axle rotate
together_______________ examples: doorknob, screwdriver The IMA of a wheel and axle = radius of wheel or rw
radius of axle ra
Gears - _____a wheel and axle with teeth around the wheel________
A gear is a _____ modified wheel and axle_______
A large gear pushes a small gear
4. Inclined Plane - ___a sloping surface used to raise objects_______
The amount of work done on moving an object is the samewhether you lift the object straight up or slide it up a ramp.
Why? Work = _____force_____ X ____distance_____ When you lift the object, the force is ______large____but the distance is ____small____ If you use a ramp, the distance is ____large______ but you use ___less____ force.
IMA of inclined plane = length of slope or Lslope
height of slope Hslope
5. Screw - _____inclined plane wrapped around a cylindrical post_______
The threads form a tiny ramp that runs from the tip to the top. 6. Wedge - _____inclined plane with one or two sloping sides_____ _____that changes the direction of the input force______________ example: knife , ax blade
Compound machines - ____two or more simple machines______ _____that work together_________________________________
