Any mechanical or electrical device that transmits or modifies energy to perform or assist in the performance of human tasks..
A mechanical device that transmits, modifies, or changes the direction of force in order to help people do work..
A apparatus in which work is done on the machine by applying a force (Effort) at one part which results in work being done by the machine in overcoming an external force (Weight or Resistance). The advantage of using a machine is that a small force can be used to overcome a larger resisting force. Optionally a small movement can be used to cause the machine to generate a larger movement.
There are six basic simple machines..
- Incline
- Wedge
- Lever
- Wheel and Axle
- Pulley
- Screw
Mechanical Advantage = W /F
The Velocity Ratio of a machine is the ratio of the distance moved by the Effort and the distance moved by the Force being overcome.Velocity Ratio = Distance moved by Effort/ Distance moved by force
In the ideal frictionless/weightless machineVelocity Ratio = Mechanical Advantage
The efficiency of a simple machineEfficiency = Work done by the machine / Work supplied to machine
The only parameter that can be determined from the machines dimensions is the velocity ratio.Machines generally follow the linear rule..
F = a + b. W
Incline Plane
One of the simplest of machines is the inclined plane..
Velocity ratio = 1 /Sin(θ)
Wedge
Velocity ratio (Single Wedge) = 1 /Tan(θ)
Velocity ratio (Double Wedge) = 2 /Tan(θ/2)
Lever
Velocity Ratio (First Class Lever) = B /A
Velocity Ratio (Second Class Lever) = (A+B ) /A
Velocity Ratio (Third Class Lever) = A / (A+B )
Wheel and Axle
Velocity ratio = R / r
Pulley
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Velocity ratio = Number of ropes Note: A very simple 2-rope pulley is shown. In practice there can be a number of rotating pulleys on the top and bottom blocks increasing the number of vertical ropes. |
Velocity ratio = 2.R /(R-r) Note:Requires use of chain with engaging sprockets to prevent slip |
Screw
Velocity ratio = R. 2.p / p