Work and Machines
Mechanical Advantage
A numerical value given to a machine which tells how many times the machine multiplies a force.
AMA Formula
Actual mechanical advantage equals force output divided by force input. AMA=Fo/Fi No unit. Only Numerical Value.
Machine
Changes the size or direction of a force to make work easier.
Mechanical Efficiency (ME)
Compares the work done by the machine with the work you put into the machine. ME is always expressed as percentage. ME will always be less than 100% because ME really tells you how well a machine is able to overcome friction. The formula for Mechanical Efficiency is: ME= (Work output/ Work input) x 100. Hint: FRICTION
Ideal Mechanical Advantage (IMA)
Deals with distances and does not account for friction. IMA: Distance Input/Distance Output or IMA: Length Input/Length Output. (NO UNIT)
Actual Mechanical Advantage (AMA)
Deals with force. Friction IS taken into account. AMA: Output Force/Input Force (NO UNIT)
Which number is always larger; AMA or IMA?
IMA
IMA Formula
Ideal mechanical advantage equals distance input divided by distance output. IMA=Di/Do No unit. Only Numerical Value
Inclined Plane Family
Inclined plane, wedge, and screw
Lever Family
Lever, Pulley,Wheel and Axle
Compound Machine
Machine made up of two or more simple machines. Compound machines have low mechanical efficiencies because they have more moving parts and thus more friction to overcome.
Why are machines not 100% efficient?
Machines are not 100% efficient because some of the work done by a machine is used to overcome friction. So work output is always less than work input.
ME Formula
Mechanical Efficiency equals work output divided by work input times 100. ME=Wo/Wi x 100 Unit %.
Work
Occurs when a force moves an object over a distance in the same direction as the force. The formula for work is: Force x Distance
Power Formula
Power equals work divided by time. P=W/t Unit is a Joule per second (J/s) or Watt (W)
Parts of Lever
Side you push on is effort, other is the resistance. And Fulcrum.
What must happen when a machine changes the size of a force?
The distance through which the force is exerted must also change. Force or distance can increase but not together.
Fulcrum
The point at which a lever rotates.
Power
The rate at which work is being done. The formula for power is: Power= Work/Time
Simple Machines
The six simple machines are lever, pulley, wheel and axle, inclined plane, wedge, and screw. acronym: LISPWW
Lever
The three types of levers are first, second, and third class. The class depends on where the input and output forces are located with respect to the fulcrum.
Watt
The unit for power. Also called Joule per second. (J/s)
Joule
The unit for work. Also called a Newton-meter. (n-m)
Work Input
The work that YOU put into a machine.
Work Output
The work that is done by the MACHINE.
List some everyday levers
Toilet Handle, Claw of a Hammer, Oar, Wheelbarrow, Baseball Bat, Pair of Scissors, and a human arm (elbow is fulcrum)
List some every day pulleys
Top of flagpole, raising window blinds, elevators, and garage doors.
Work Formula.
Work equals force times distance. W=F x d Unit is a Newton-meter (n-m) or Joule (J)
Know the work and machines map!
Work: is defined as Force applied over Distance and is made easier by machines such as a Lever. Work: Done by machines is calculates as Mechanical Efficiency which is Work Output divided by Work Input.Work: Done by machines is calculated as Mechanical Advantage which is Output Force divided by Input force.
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