Machines What is a machine? How do you calculate the M.A. and Efficiency of a machine?

INPUT Input Force – force you exert on a machine Input distance – how much the input force moves the machine Input Work = Input F x Input d

OUTPUT Output Force – the force the machine exerts on an object Output distance – the distance over which the machine exerts the output force Output Work = Output F x Output d

Work and Machines A machine makes work easier by changing force, distance, or direction It DOES NOT multiply work The amount of output work can never be greater than the amount of input work

What is a machine? -A machine is a device that allows you to do work in a way that is easier. A machine changes at least one of three factors: -Force -Distance -Direction

Changing Force - Output force > Input force - Output distance < Input distance - Example: ramp - f x D  F x d

Changing Distance -Output Force < Input Force -Output distance > Input distance -Examples: hockey stick, baseball bat, chopsticks, pedaling a bike -F x d  f x D

Changing Direction -No change in force or distance -Only changes direction -Example: weight lifting machine -F x d  d x F

Mechanical Advantage -Definition: the number of times a machine increases a force exerted on it -Formula: MA = Output F/Input F

Mechanical Advantage -Increasing Force – when the output force is greater than the input force, the MA of the machine is > 1

Mechanical Advantage -Increasing Distance – when the machine increases d, the output force is less than the input force, so the MA is < 1

Mechanical Advantage -Changing Direction – if only the direction changes, the input force will be the same as the output force, so MA = 1

Calculating Mechanical Advantage

Efficiency -MA is ideal -In the real world, output work is always less than input work -Efficiency compares output work and input work -% - higher is more efficient

Efficiency -Friction – in every machine, some work is wasted overcoming the force of friction -Equation: -E = (output W/input W) x 100%

Real vs Ideal -100% efficiency is ideal -In reality, measured efficiency is less than 100%

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