Slide 1
Turn around a support
A lever is a rigid member that turns about a fulcrum. Moving the effort farther from that pivot can increase the force delivered to a load.
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The relevant distance is the perpendicular distance from the pivot to the force’s line of action. An angled push may have a smaller turning effect than the same force applied perpendicular to the lever.
Slide 2
Balance the turning effects
For a stationary ideal lever, opposing torques balance. Force multiplied by its lever arm gives the turning effect about the pivot.
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A 10-newton effort acting 0.6 metres from the pivot can balance 30 newtons at 0.2 metres. Both torques are 6 newton metres, ignoring the lever’s own weight.
Slide 3
Pay with extra movement
A force advantage comes with a distance tradeoff. The effort end travels farther while the load end moves a shorter distance.
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For the same small angular turn, travel is proportional to distance from the pivot. The longer effort arm therefore provides the distance needed to conserve work in an ideal lossless mechanism.
Slide 4
Place the parts for the task
Different arrangements of pivot, effort and load change the lever’s behaviour. Some favour force, while others favour speed or reach.
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Tweezers place effort between the pivot and tip, sacrificing force advantage for useful tip travel and control. Calling something a lever does not imply that it always multiplies force.
Slide 5
Real levers also flex
Friction, weight and deformation reduce ideal performance. A practical lever must carry its loads without excessive bending or damage.
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Increasing length also increases space requirements and may increase structural demands. Designers balance mechanical advantage with stiffness, clearance and the effort needed to move the lever itself.
Sources
- Simple Machines
OpenStax
- Basics of Mechanical Design
MIT Center for Bits and Atoms