Extra work (overcoming the gravity of the lever itself, the work done by friction w extra =W always -W useful)

Total hours (w total =FS)

Pulley block: useful (w useful =Gh)

Extra work (work done to overcome the weight of moving pulleys, ropes and friction)

①W Extra = W Total-W used

(2) If the rope weight and friction force are not considered, W extra =G moves H)

Total hours (w total =FS)

Inclined surface: useful work (w useful =Gh)

Extra work (work to overcome friction)

①W Extra = W Total-W used

② WEEXTRA = FL) Note: F refers to the friction force L refers to the length of the inclined plane.

Total work (W total =FL) Note F refers to the pulling force.

Calculation of mechanical efficiency

Lever: η=W Useful ÷W Total =Gh÷FS

Where g is the gravity of the lifted weight, h is the height of the weight, f is the strength, and s is the moving distance of the strength point.

Pulley or wheel set:

① Lifting heavy objects: 1, η=W Useful ÷W Total =Gh÷FS=G÷nF

2. Regardless of the rope weight, the friction η=Gh÷(Gh+G moving h)=G÷(G+G moving).

② Horizontal uniform pulling: η=W Useful ÷W Total =fs object ÷Fs rope =f÷nF.

Inclined plane: ①η=W Useful ÷W Total =Gh÷FL

②η= Gh \u( Gh+fL)

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This is all within the scope of grade three.