Editing Lever (section)

== Force and levers ==
[[File:Lever Principle 3D.png|thumb|right|A lever in balance]]
A lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which means there is no friction in the hinge or bending in the beam. In this case, the power into the lever equals the power out, and the ratio of output to input force is given by the ratio of the distances from the fulcrum to the points of application of these forces. This is known as the '''law of the lever'''.

The mechanical advantage of a lever can be determined by considering the balance of [[Moment (physics)|moments]] or [[torque]], ''T'', about the fulcrum. If the distance traveled is greater, then the output force is lessened.

<math display="block">\begin{align}
T_{1} &= F_{1}a,\quad \\
T_{2} &= F_{2}b\!
\end{align}</math>

where F<sub>1</sub> is the input force to the lever and F<sub>2</sub> is the output force. The distances ''a'' and ''b'' are the perpendicular distances between the forces and the fulcrum.

Since the moments of torque must be balanced, <math>T_{1} = T_{2} \!</math>. So, <math>F_{1}a = F_{2}b \!</math>.

The mechanical advantage of a lever is the ratio of output force to input force.

<math display="block">MA = \frac{F_{2}}{F_{1}} = \frac{a}{b}.\!</math>

This relationship shows that the mechanical advantage can be computed from ratio of the distances from the fulcrum to where the input and output forces are applied to the lever, assuming a weightless lever and no losses due to friction, flexibility, or wear. This remains true even though the "horizontal" distance (perpendicular to the pull of gravity) of both ''a'' and ''b'' change (diminish) as the lever changes to any position away from the horizontal.