Simple Machines
Definition:
A device that changes the direction of the Force that is applied to do a job.
For Example:
Ramp
In order to lift a crate straight up, you would use a ramp – right?
You want to lift a vertical height
The ramp changes the vertical lift to a diagonal
It takes less force to push an object at an angle to gravity than it is to pick it up in line with gravity.
Ramp
20N
40N
But, since it is a longer distance, you are doing more work with less effort.
So, it doesn't seem as hard of work using the ramp
Ramp Distance
Ver
tical
Dis
tanc
e
Simple machines are Separated into two Families:
1. Lever Family
2. Incline plane Family
Lets start with the levers . . .
TheLever Family
Terminology first - - Fulcrum – The point at which the lever pivots.- Input force – The force that is applied by you. Your hand. By pushing or pulling.
- Output force – The force that is applied to the object
- Also called the effort arm
- Also called the resitance arm
1st Class Lever -- The fulcrum is between the two ends
- The input and output are at the ends
input outputOrVis versa
Fulcrum
Example?
input
output
Fulcrum
Crow bar
2nd Class Lever -- The fulcrum is is at one end
- The input is at the opposite end of fulcrum
inputoutput
Fulcrum
- The output is between input and fulcrum
Example?
inputoutput
Fulcrum
Wheel Barrow
Don’t forget the other example- you have to draw it.
3rd Class Lever -- The fulcrum is is at one end again
- The output is at the opposite end of fulcrum
input output
Fulcrum
- The input is between input and fulcrum
Example?
Catapult
input
output
Fulcrum
Wheel and Axle-- A lever that rotates in a circle around a
center point or fulcrum
- There is the obvious wheel that is a wheel and axle but there are some that are not so obvious.
Center
Point
Rotation
Like this --
Central Axis
Rotation
OR like this --
Central Axis
Rotation
There does not have to be an actual wheel. It just has to spin around a central point.
OR like those
Pulley -
- Is a wheel and axle with a string, rope, chain, or belt the is pulled around the wheel part.
The Incline plane
Family
Simple Inclined Plane - - Which is . . . ?
- A Ramp
Wedge- - When you butt one ramp, - Against another
- It is a wedge.- They are always used for cutting or splitting of some kind
- Examples – Scissors, Knives,
Shears, Shovels, Spatulas, nails ect . .
Screw- - A ramp that is wrapped around a central axis
- Used for - Fasteners
- Augers
- Clamps
-Mechanical Advantage- The numerical value of
how much your force is multiplied using a machine.
- Formulas-
Input distanceOutput
Distance
Output ForceInput Force
MA=
MA=
OR
Example -
If you had a 1st class lever that you wanted to lift a rock with and the input distance was 4 feet and the output distance was only 1 foot, What is the mechanical Advantage?
Input distance
= 4 ft
Fulcrum
Output distance
= 1 ft
Input distance
= 4 ft
Fulcrum
Output distance
= 1 ft
Input distanceOutput
Distance
MA=
MA=
4 feet
1 foot= 4
That means that your force that that is pushing up is 4 times as much on the rock you are lifting. If you push with 10 lbs, you can lift 40lbs.