Wheel and Axle Lever Machines Pulley Screw Wedge

Wheel and Axle Lever Machines Pulley Screw Wedge Inclined Plane

What is a Machine? • A device that makes doing work easier • Two divisions – Simple machines – Compound Machines • Work against friction and gravity.

How do Machines make work Easier? • Increase Force – (ex: car jacks) • Increase the distance a force is applied – (ex: using a ramp) • Changing the direction of an applied force – (ex: ax blade)

Simple Machines • Machines that does work with only one movement of the machine

Input force & Output force • Input Force – Force applied to the machine – Symbol = Fin • Output Force – Force applied by the machine – Symbol = Fout

Input Work & Output Work • Input Work – Work done by you on a machine – Symbol = Win • Output Work – Work done by the machine – Symbol = Wout

Input & Output Work: The Relationship • Input work equals Output work in an ideal machines • Win = Wout • Why? – Law of conservation of Energy • Energy is not created nor destroyed

What is Mechanical Advantage? • Is the number of times that a machine increases an input force • Two Versions – Actual Mechanical Advantage – Ideal Mechanical Advantage

Mechanical Advantage Link

Actual Mechanical Advantage • Determined by measuring the actual forces on a machines • Ratio of the output force to the input force

Actual Mechanical Advantage Formula AMA = Fr / Fe • AMA= actual mechanical advantage • Fr= resistance force (output force) • Fe=effort force (input force) • AMA has no unit • Fr & Fe has the unit of “N”

AMA Formula Practice 1) What is the actual mechanical advantage of a machine who’s input force is 30 -N but produces an output force of 90 -N? 2) You test a machine and find that it exerts a force of 10 N for each 2 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

Example Problems: 1. A worker applies an effort force of 20 N to pry open a window that has a resistance force of 500 N. What is the mechanical advantage of the crowbar? 2. Find the effort force needed to lift a 2000 N 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 2500 N. The carpenter applies an effort force of 125 N. What is the mechanical advantage of the hammer? 4. A force of 500 N is needed to lift a 200 kg stone, what is the MA of the simple machine?

Cont… 5. What is the force required to lift a 12 kg 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?

Ideal Mechanical Advantage • Is the mechanical advantage in the absence of friction • Because friction is always present, the actual mechanical advantage of a machine is always less than the Ideal

Ideal Mechanical Advantage Formula IMA = de / dr • IMA = ideal mechanical advantage • de = displacement of effort force (input distance) • dr = displacement of resistant force (output distance) • IMA has no unit • de and dr has the unit of meters

IMA Formula Practice 1) A woman drives a car up onto wheel ramps to perform some repairs. If she drives a distance of 1. 8 meters along the ramp to raise the car 0. 3 meter, what is the IMA? 2) A construction worker moves a crowbar through a distance of 4 meters to lift a load 0. 5 meter off the ground. What is the IMA of the crowbar?

Calculate IMA: . 3 m 9 m IMA = 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?

What is efficiency? • The percentage of work input that becomes work output • Because there is always some friction, the efficiency of any machine is always less than 100 percent %

Efficiency Formula • Wout = work output (J) • Win = work input (J)

Efficiency Formula Practice 1) You have just designed a machine that used 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?

Machines usually work against GRAVITY and FRICTION. . Example: 1. Lifting a car 2. Opening a jar lid

A sloping surface (ex: ramp) Click on the dude to learn more.

A screw is an inclined plane wrapped around a post. Ex: A Jar lid Click on the light bulb to learn more.

Two inclined planes make a wedge. An inclined plane with one or two sloping sides (ex: knife)

A shaft/axle attached to the center of a larger wheel so that both rotate together (ex: door knobs) Wheel Axle 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 (ex: wishing well)

Click Here to Learn More Lever Load Fulcrum

LEVERS a bar that is free to pivot or turn about a fixed point Effort Arm – part of lever where force is applied “FORCE” Resistance arm – part of lever that exerts resistance force “LOAD” FULCRUM – fixed point of a lever

3 TYPES OF LEVERS Based on the positions of the effort force, resistance force and the fulcrum…

FIRST CLASS Fulcrum is located between the resistance and the effort force http: //www. usoe. k 12. ut. us/curr/scienc e/sciber 00/8 th/machines/sciber/lever 1. htm (RFE)

SECOND CLASS Resistance is between the effort force and the fulcrum (FRE) http: //www. usoe. k 12. ut. us/curr/science/sciber 00/8 th/machines/sciber/lever 2. htm

THIRD CLASS Effort force is between the resistance force and the fulcrum. http: //www. usoe. k 12. ut. us/curr /science/sciber 00/8 th/machine s/sciber/lever 3. htm (FER) MA is always less than one - ? ? ?

What are Compound Machines? • When two or more simple machines operate together • Example: Can Opener – Wheel & Axle – Lever – Wedge