Use the right ratio to connect measured forces with input and output movement.
Select a page to enlarge it.
Mechanical advantage, MA, is output force divided by input force. The forces must describe the same machine operating under comparable conditions. Use newtons for both; the units cancel.
In these notes, speed ratio, SR, means input distance divided by output distance over the same time interval. It also equals input speed divided by output speed for a steady mechanism. Label the numerator and denominator.
An ideal machine with negligible losses has MA = SR. Real measured MA is usually lower for the same geometric motion ratio because more input is needed to overcome losses. Geometry can predict an ideal ratio; a force measurement tests actual performance.
An MA below 1 means the output force is smaller than the input force. A mechanism may instead provide greater output travel, greater speed or precise positioning. A bicycle high gear and many sporting levers trade force for movement.
Change one measurement, predict the result, then compare the calculated account. These are editable teaching measurements, not a physical simulation.
The Organic Chemistry Tutor · Mechanism in action
Choose one worked lever or ramp example. Record the two forces and the two travel distances; identify which ratios are being compared.
A machine has MA = 2.4 and SR = 3 for one steady lift. What is its efficiency?
2.4 ÷ 3 × 100% = 80%. Some input work transfers to less useful outputs.
Create a measured dataset with MA below SR. Show that the work calculation gives the same efficiency.
Apply it to the design challenge →Read further: OpenStax · Simple Machines →
