 # Name ________________________________ Physical Science

## Presentation on theme: "Name ________________________________ Physical Science"— Presentation transcript:

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 J Example #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 = 25 Example #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 fulcrum
example - 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 same whether 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_________________________________