Study guide for simple machines test
· Read chapter 8
· Know that work happens only when the object moves in the direction of the force
· Work = input force X distance the load moves
Know
· input force (effort) is what you do to the machine
· output force (load) is the weight on the load in Newtons
· simple machines do not change the amount of work done…they make it easier by …multiplying the input force or changing the direction of the force
· how each machine helps you do work:
Ø 1st class lever changes the direction of the force and can multiply the input force (effort)
Ø 2nd class lever multiplies input force (effort)
Ø 3rd class used for pushing & hitting multiplies the distance the effort (input force) moves …like a broom
Ø Pulleys multiply input force by increasing distance and some also change direction (distance is the rope length you pull on)
Ø Wedges & inclined plane multiply input force by increasing distance of slope length
Ø Screws multiply the input force by increasing the distance (distance is the number of threads which = number of turns)
Ø Wheel & axle multiplied input force by increasing the distance ( distance is the circumference of the wheel)
Ø When a simple machine multiplies the input force there is a tradeoff: THE DISTANCE THE INPUT FORCE (EFFORT) MOVES IS INCREASED
· work input is the work you do on the machine
· work output is the work the machine does on the load
· Mechanical advantage is the number of times the machines multiplies your input force.
· AMA= output force/input force
· How to calculate MA for each type of simple machine:
Ø IMA levers =length of effort arm/ length of resistance arm
Ø IMA inclined plane= length of ramp/height of ramp
Ø IMA of wedges = slope of wedge/ thickness of wedge
Ø IMA of pulleys = number of load bearing ropes
· Definitions of all vocabulary
· Formula for work w=fd
· Friction causes machines to have an efficiency of less than 100%
Ø AC ONLY: MA of screw= circumference / pitch,
Ø AC ONLY: ME (mechanical efficiency)= output work/input work X 100