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CENTRE OF MASS

& ROCKET

PROPULSIONMECHANICS & PROPERTIES OF MATTER

GROUP VII

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CONTENTCentre of Mass What is Centre of Mass? Centre of Mass of symmetrical shape The Centre of Mass point for two mass system

• 2D• 3D

Rocket Propulsion

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CENTRE OF MASS-(CM)• The location where all the mass of system could

be concentrated to be located.•Make responses to the external forces and

torques.• Distribution of mass is balanced around the CM.•Weighted average position coordinates defines

the position.

M1 M2CM

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CENTRE OF MASS OF

SYMMETRICAL SHAPES

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CM OF TWO IDENTICAL MASSES

l lm m

CM

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UNIFORM ROD

ll

CM

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SOLID TRIANGLE PLATE

x

x x

CM

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CIRCLE

r

r

rr

CM

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CUBOID

CM

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THE CENTRE OF MASS POINT FOR

TWO-MASS SYSTEM

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CMm1 m2

x

x1x2

Reference axis𝑥=

𝑚1 𝑥1+𝑚2𝑥 2𝑚1+𝑚2

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If the system is consist of “n” no. of mass particles,the position of the CM will be,

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In the case of a 3D system,Y

Z

X

r1

rn

R(n-1)

R(n-2)r5

r4

r2

r3

m1

m5

m(n-1)

m4

m3

m2

mn

m(n-2)

CM

Position vector of CM is =x+y+z

{xi+yi+zi}

Where the position vector of mass of the system

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ROCKET PROPULSION

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• Based on the concept of “CONSERVATION OF MOMENTUM”

V

M

at time “t”

M

V+

Ve

Δ𝑚

at time “t+t”

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