Levers and Mechanical Advantage flashcards

Look at what is in the middle (memory aid F-L-E for 1-2-3). Fulcrum in the middle: first class. Load in the middle: second class. Effort in the middle: third class.

$F_e\times d_e=F_L\times d_L$: effort times its distance from the fulcrum equals load times its distance. Example: 300 N rock at 0.5 m needs 100 N at 1.5 m.

$\text{IMA}=\frac{d_{effort}}{d_{load}}$, both measured from the fulcrum; unitless. A 1.6 m effort arm and 0.40 m load arm give IMA 4, so effort = load / 4.

$\text{AMA}=\frac{F_{out}}{F_{in}}$; efficiency = AMA / IMA × 100%. AMA is always less than IMA because of friction. IMA 6 with AMA 4.8 gives 80% efficiency.

Second class (wheelbarrow, nutcracker) always has IMA above 1. Third class (tweezers, broom, forearm) always has IMA below 1 but gains speed and reach. First class can go either way.

No. Work in equals work out at best. If force is multiplied by 5, the load moves only 1/5 as far. Any choice claiming more work out than in, or over 100% efficiency, is wrong.

Multiply the stages: ${\text{IMA}}_{total}={\text{IMA}}_1\times {\text{IMA}}_2$. Stages of 3 and 4 give 12, not 7. Nail clippers are an example.

Convert mass to weight first: $W=mg$. A 20 kg box at 0.5 m makes about 200 N × 0.5 m = 100 N·m (with g = 10), not 10 N·m. Also convert cm to m before computing N·m.