Simple Machine

Topics: Simple machine, Mechanical advantage, Force Pages: 12 (3810 words) Published: April 5, 2012

Joemarie A. Martinez
1-D CE
Simple machine

Simple machines make work easier by multiplying, reducing, or changing the direction of a force. The scientific formula for work is w = f x d, or, work is equal to force multiplied by distance. Simple machines cannot change the amount of work done, but they can reduce the effort force that is required to do the work! As you can see by this formula, if the effort force is reduced, distance is increased.

These simple machines fall into two classes: (i) the inclined plane, wedge, screw characterized by the vector resolution of forces and movement along a line, and (ii) the lever, pulley, wheel and axle characterized by the equilibrium of torques and movement around a pivot. Wedges and screws are both a type of inclined plane; pulleys and wheels and axles are both a form of lever

A simple machine is an elementary device that has a specific movement (often called a mechanism), which can be combined with other devices and movements to form a machine. Thus simple machines are considered to be the "building blocks" of more complicated machines. This analytical view of machines as decomposable into simple machines first arose in the Renaissance as a neoclassical amplification of ancient Greek texts on technology, and is still a central part of engineering in today's age of applied science.

For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle. Between the simple machines and complex assemblies, several intermediate classes can be defined, which may be termed "compound machines" or "machine elements". The mechanical advantage of a compound machine is simply the product of the mechanical advantages of the simple machines of which it is composed.

There are six types of simple machines
Inclined plane

An inclined plane is a board or other flat surface set at an angle to the horizontal. Since the force needed to push an object up an inclined plane is less than the force needed to lift the same object, inclined planes reduce the amount of force necessary to do a job. A ramp is an example of an inclined plane.

Renaissance scientists added the inclined plane to the five of simple machines described by Hero of Alexandria. It is a flat surface that lies at an angle relative to level ground used to form a ramp to raise and lower a load. The force required to lift the load is reduced by pulling it up the ramp.

Assuming the movement of the load does not dissipate or store energy, the mechanical advantage of an inclined plane is the ratio of the length of the ramp to the height lifted. -------------------------------------------------

Mechanical advantage of inclined plane
The mechanical advantage of an inclined plane is the ratio of the weight of the load on the ramp to the force required to pull it up the ramp. If energy is not dissipated or stored in the movement of the load, then this mechanical advantage can be computed from the dimensions of the ramp. In order to show this, let the position of a rail car A on along ramp be given by the coordinates

where R is the distance along the ramp. The velocity of the car up the ramp is given by

Because there are no losses, the power used by F to move the load up the ramp equals the power out, which is the vertical lift of the weight W of the load. The input power pulling the car up the ramp is given by

and the power out is

Equate the power in to the power out to obtain the mechanical advantage as

The mechanical advantage of an inclined can also be calculated from the ratio of length of the ramp L to its height H, because the sine of the angle of the ramp is given by


Example: If the height of a ramp is H = 1 meter and its length is L = 5 meters, then the mechanical advantage is


A wedge is shaped like two inclined planes placed back to...
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