Theory of Machine
Two systems shall be dynamically equivalent when

All of these
M.I. of two about an axis through e.g. is equal
G. of two coincides
The mass of two are same

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Theory of Machine
Open pairs are those which have

Two elements that permit relative motion
Surface contact between the two elements when in motion
Point or line contact between the two elements when in motion
Elements of pairs not held together mechanically

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Theory of Machine
The secondary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank)

m.ω².r cosθ
m.ω².r (sin 2θ/n)
m.ω².r sinθ
m.ω².r (cos 2θ/n)

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