7th grade- work and simple machines

8/10/2019 7th Grade- Work and Simple Machines

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What is the Formula for Pressureand what units are used to measureit?

Pressure = Force / area

Unit of measurefor Pressure is thePascal: 1Pa = 1N/m2

SWBAT: Identify hen or! is done onan o"#ect and ill "e a"le to calculatethe or! done on an o"#ect


2/26

$The %ressure e&erted "y a mo'in( stream ofa )uid is less than the %ressure of thesurroundin( )uid*+ This statement is a"outhich %rinci%le that e learned "efore the"rea! ,

Bernoulli-s %rinci%le

The faster the )uid mo'es. the less %ressure

it e&erts on the surface of the o"#ect

SWBAT: Identify hen or! is done on ano"#ect and ill "e a"le to calculate the or!done on an o"#ect


3/26

Physical Science

Work & Machines


4/26

What is Wor!, Work is force exerted on an object that

causes the object to move some distance

orce ithout mo'in( a distance yields N0W033

Work = Force x Distance

SI Unit for work is the Joule

1 Joule = 1Newton x 1 Meter
http://www.brainpop.com/science/motionsforcesandtime/work/https://www.brainpop.com/science/motionsforcesandtime/work/https://www.brainpop.com/science/motionsforcesandtime/work/http://www.brainpop.com/science/motionsforcesandtime/work/


5/26

Word Problems

Word problems can be confusing but w! some practicethe"#re not that bad$ %ere are a few hints to make them

easier 1$ &e sure "ou remember the 'Need(to()now* formulas

S =d!t A = 4f5 4i6 = 7A 6 W=&86 Poer = Wor!/Time

Time In the word problem be sure "ou know the units for each of the

+ariables in the particular formula being discussed$ ,istance - Meter .orce - Newton /olume ( cm0or iter

2$ In the word problem3 all but one of the +ariables is told to "ou in

one wa" or another$ Identif" what +ariable is being asked to sol+e3

then plug in the remaining +ariables to the formula

Sol+e it44 Make sure "ou also keep track of the units


6/26

9o much or! %erformed: %ow much work is performed if "ou appl" 56 newtons of force on a box

causing it to mo+e 0 meters7

W = . x ,

W = 56N x 0m = 266 Nm

266 J = 266 Nm

%ow much work is performed if "ou appl" 08 newtons of force and mo+e a

wagon 9$0 meters:

W = . x ,

W = 08N x 9$0m = 16;$1 Nm

16;$1 J = 16;$1 Nm

%ow much work is performed if "ou appl" 115 newtons of force on a car that

is stuck in the mud and doesn#t mo+e:7

W = . x ,

W = 115N x


7/26

9o much force reuired:

9o much force as reuired to mo'e an o"#ect; meters if oules of or! ere e&%ended, ormula: Work = Force x Distance

Need to solve for Force, w= ! " # D=$%

! " = F x $%

! N% / $% = F

! N% / $% = F

&!N = F


8/26

9* ? read? %(s*


9/26

8o No: 9o much force as reuiredto mo'e an o"#ect 2 meters if 2

>oules of or! ere e&%ended,

W= & 8 .so if e no 2>= & 2m.

e di'ided "oth sides "y 2 and (et2G*2 N

SWBAT: H&%lain ho machines or!

easier and calculate the mechanicalad'anta(e of a machine


10/26

What is a 7achine, A de'ice that ma!es or! easier or more

eecti'e A machine ma!es or! easier "y chan(in( the

amount of force. the distance covered or "ychan(in( the direction of the force


11/26

7echanical Ad'anta(e A machine-s mechanical advanta'e is the number of

times a force exerted on a machine is multi%lied (deal %echanical )dvanta'e has no units * the+

cancel each other out when doin' the mathroblem

%echanical )dvanta'e= -utut force/(nut force


12/26

HJciency of a 7achine The amount of or! o"tained from a machine is

alays less than the amount of or! %ut into it*This is "ecause or! is lost to friction*

.cienc+ = outut work / inut work x 0112

Remember that

work = force x

distance


13/26

Simple Machines


14/26

Inclined Plane > plane is a flat surface$ When that plane is inclined3 or slanted3 it can

help "ou mo+e ob?ects across distances$ >nd3 that@s work4 > commoninclined plane is a ramp$ ifting a hea+" box onto a loading dock is much

easier if "ou slide the box up a ramp((asimple machine$

M> = length of incline ! height of incline
https://www.brainpop.com/technology/simplemachines/inclinedplane/https://www.brainpop.com/technology/simplemachines/inclinedplane/


15/26

Wedge ou can use the edge of an inclined plane to push things apart$ Ahen3 the

inclined plane is a wedge$ So3 a wedge is actuall" a kind of inclined plane$>n axe blade is a wedge$ Ahink of the edge of the blade$ It@s the edge of a

smooth slanted surface$


16/26

Screw an inclined %lane ra%%ed

around a cylinder A scre can con'ert a

rotational force CtorueE to alinear force and 'ice 'ersa*
http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Torque


17/26

A ram% 2 feet in len(th is feet in hei(ht* What isthe mechanical ad'anta(e of this sim%le machine

7A = len(th of incline / hei(ht of incline

2/= @

7echanical Ad'anta(e= @

SW&>A(calculate the mechanicalad'anta(e of a machine and descri"ecom%ound machines


18/26

Lever

>n" tool that pries something loose is a

le+er$ > le+er is a rigid bar that Bpi+otsB Cor

turnsD against a BfulcrumB Cor a fixed pointD$

M$>$ = Effort Cinput forceD! oad Coutput forceD
https://www.brainpop.com/technology/simplemachines/levers/https://www.brainpop.com/technology/simplemachines/levers/


19/26

1stClass Levers Notice how

Ahe input F output forces are in opposite directions

Ahe fulcrum is between the input F output forces

Examples include nail remo+er3 paint can opener scissors3 seesaw


20/26

2ndClass Levers

Notice how7

Ahe input F output

forces are in the

same direction Input force is farther

awa" from the

fulcrum than the

output force

Examples include7

wheel barrow3 door3

nutcracker


21/26

3rdClass Lever Notice how7

Ahe input F output

forces are in the same

direction

Ahe input force is closer

to the fulcrum than the

output force

Examples include rake3

sho+el3 baseball bat and

fishing pole


22/26

What Class of Lever

1

8G

9

6

0

2

5


23/26

Wheel and !"le to circular o"#ects attached to(ether a"out a

common a&is Wheel is the lar(e cylinder

A&le is the small cylinder
https://www.brainpop.com/technology/simplemachines/wheelandaxle/https://www.brainpop.com/technology/simplemachines/wheelandaxle/


24/26

P#lley In a pulle"3 a cord wraps around a wheel$ >s the wheel

rotates3 the cord mo+es in either direction$ Now3 attach

a hook to the cord3 and "ou can use the wheel@s

rotation to raise and lower ob?ects$
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25/26

Kom%le& 7achines Kom"inin( to or more sim%le

machines to or! to(ether

H&am%les:

Kar #ac! combinesed(e and scre Krane or to truc! combinesle'er and

%ulley


26/26

9and outs on Sim%le machine.eJciencies. or!L

7th grade- work and simple machines

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