Work & Machines

Work Work

transfer of energy through motionforce exerted through a

__________

W = Fd

Distance must be in direction of ______!

W: work (___)F: force (____)d: distance (__)

1 J = 1 N·mFWd

Try these!!! A mover lifts a 98 N box 1.8 m from the

ground to a shelf. How much work is done on the box?

Alice has a heavy pocketbook. Each morning to lifts it off the ground and puts it on the counter that is 1.6 m from the floor. In doing this she does 8 J of work. How much does the pocketbook weigh?

PracticePick up a Work worksheet from the front table & complete #1-10

Do you want to do all the work yourself?

Of course not!What do we use that helps us do

work?

MACHINES!!!

Machines Machines Machines Machines II. The Simple Machines

Lever Pulley Wheel & Axle

Inclined Plane Screw Wedge

http://www.youtube.com/watch?v=grWIC9VsFY4&safety_mode=true&persist_safety_mode=1

http://www.youtube.com/watch?v=qybUFnY7Y8w&safety_mode=true&persist_safety_mode=1

http://www.youtube.com/watch?v=lCYg_gz4fDo&safety_mode=true&persist_safety_mode=1

http://rubegoldberg.com/

A. LeverLever

a bar that is free to pivot about a fixed point, or ____________

“Give me a place to stand and I will move the Earth.”

– Archimedes

Engraving from Mechanics Magazine, London, 1824

Effort arm

Resistancearm

________

Lever Ideal Mechanical Advantage (IMA)

frictionless machine

r

e

L

LIMA

Effort arm length

Resistancearm length

Le must be greater than Lr in order to multiply the force.

LeverFirst Class Lever

can increase force, distance, or neither

changes direction of force

r

e

L

LIMA

LeverSecond Class Lever

always increases __________.

r

e

L

LIMA

LeverThird Class Levers

always increases __________.

r

e

L

LIMA

PulleyPulley

grooved wheel with a ______ or chain running along the groove

a “flexible first-class lever”

LeLr

F

Pulley Ideal Mechanical Advantage (IMA)

equal to the number of supporting ____________

IMA = 0 IMA = 1 IMA = 2

PulleyFixed Pulley

IMA = ____

does not increase force

changes direction of force

PulleyMovable Pulley

IMA = ____increases force

doesn’t change direction

B. PulleyBlock & Tackle

combination of fixed & movable pulleys increases force (IMA = 4) may or may not change ___________

Wheel and AxleWheel and Axle

two wheels of _________sizes that rotate together

a pair of “rotatinglevers”

Wheel

Axle

Wheel and Axle Ideal Mechanical Advantage (IMA)

effort force is usu. applied to wheel

axle moves less _________ but with greater force

r

e

r

rIMA

effort radius

resistance radius

Problems You use a 160 cm plank to lift a large

rock. If the rock is 20 cm from the fulcrum, what is the plank’s IMA?

GIVEN:

Lr = 20 cm

Le = 140 cm

IMA = ?

WORK:

IMA = Le ÷ Lr

IMA = (140 cm) ÷ (20 cm)

IMA = 7

IMA

Le

Lr

20cm

160cm

Problems A crank on a pasta maker has a radius

of 20 cm. The turning shaft has a radius of 5 cm. What is the IMA of this wheel and axle?

GIVEN:

re = 20 cm

rr = 5 cm

IMA = ?

WORK:

IMA = re ÷ rr

IMA = (20 cm) ÷ (5 cm)

IMA = 4

IMA

re

rr

5 cm 20 cm