WedgeInclined Plane

Screw

Wheel and Axle

Lever

Pulley

MachinesA device that eases a load

by changing magnitude or direction of a force as it transmits energy to the task

Machines involve 2 types of WORK (W = F x d )

1. Work done ON the machine (Win)

Win = Fe x de

2. Work done BY the machine (Wout)

Wout = Fr x dr

Force exerted ON the machine

(effort force)

Distance resulting from effort force

Force exerted BY the machine

(resistance force)

Distance traveled against resistance

Remember… Conservation of Energy??

You never can get more energy out of a machine than you put in!!

Wout can’t be greater than Win

In FACT…

Wout is always smaller than Win!!

WHY??

Energy lost in the form of heat (friction)

(by machine)

(on machine)

Mechanical Advantage (MA)

The number of times a machine multiplies the effort force

Mechanical Advantage

Mechanical Advantage Link

Actual Mechanical Advantage

vs. Ideal Mechanical Advantage

MA (mechanical advantage) Number of times a machine multiplies

the effort force

AMA (actual mechanical advantage) resistance force/effort force = Fr/Fe

IMA (ideal mechanical advantage)length of effort arm/length of resistance arm =

de /dr

Efficiency

Efficiency = Work out /Work in x 100

Efficiency is less than 100% for real machines!!

Example Problems:1. A worker applies an effort force of

20N to pry open a window that has a resistance force of 500N. What is the mechanical advantage of the crowbar?

1. Find the effort force needed to lift a 2000N rock, using a jack with a mechanical advantage of 10.

Cont…3. A carpenter uses a claw hammer to pull a nail from a board. The nail has a resistance of 2500N. The carpenter applies an effort force of 125N. What is the mechanical advantage of the hammer?

4. A force of 500N is needed to lift a 200kg stone, what is the MA of the simple machine?

Cont…5. What is the force required to lift a 12kg object if the MA of the machine is 5?

6. What is the efficiency of a machine that 500 J of work was put into the machine and it produced 400 J of work?

Calculate IMA:

3 m 9 mIMA =

7. You use a crow bar 140 cm long as a lever to lift a large rock. The rock is 20 cm from the fulcrum, what is the IMA of the lever?

.

Machines usually work against GRAVITY and

FRICTION..Example: 1. Lifting a car 2. Opening a jar lid

Click on the dude to learn more.

A screw is an inclined plane wrapped around a post.

Click on the light bulb to learn more.

Two inclined planes make a wedge.

Try to catch the saw to learn more.

Axle

Wheel

Click on the windmill to learn more.

Wheel

Rope This box is easier to lift because of the pulley. Click on it to learn more.

a grooved wheel with a rope or chain running along the groove

                             

Fulcrum

Lever

Load

Click Here to Learn More

LEVERSa bar that is free to pivot or turn about a fixed point

FULCRUM – fixed point of a lever

Resistance arm – part of lever that exerts resistance force

“LOAD”

Effort Arm – part of lever where force is applied

“FORCE”

3 TYPES OF LEVERSBased on the positions of the effort

force, resistance force and the fulcrum…

FIRST CLASS

                                                      

Fulcrum is located between the resistance and the effort force

(RFE)http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/lever1.htm

SECOND CLASS

http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/lever2.htm

                     

Resistance is between the effort force and the fulcrum

(FRE)

THIRD CLASS

                                                         Effort force is between the resistance force and the fulcrum.

(FER)

MA is always less than one - ???

                             

http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/lever3.htm

Click above