Sun January 30, 2011 By: Arnab Dutta

ina closed isolated system how do the constituting masses interact so as to conserve the momentum of the system????

Expert Reply
Mon January 31, 2011
Dear student,
What is Conservation of Momentum?
The conservation of momentum principle states that 'In any closed system, with no external forces acting, the total momentum of the system does not change.' This could be alternatively stated as 'The vector sum of all momenta in a closed system, unaffected by external forces is zero.' The conservation of momentum principle is a consequence of Newton's first law of motion. When two bodies in an isolated system collide, their total momentum before collision is equal to their total momentum after collision. This can be stated as:

ΔP1 + ΔP2 = 0

where ΔP1 is the change in momentum of the first particle while ΔP2 is the change in momentum of the second particle.

Conservation of Momentum Equation
The conservation of momentum formula is stated as follows. For a collision between two particles in an isolated system, the total momentum before and after collision is constant.

M1U1 + M2U2 = M1V1 + M2V2

Here M1 is the mass of the first particle, M2 is the mass of the second particle, U1 is initial velocity of first particle, U2 is initial velocity of second particle and V1 and V2 are the final velocities of the first and second particles respectively.
Conservation of Momentum Examples
Examples of conservation of linear momentum abound in everyday life. Wherever there is collision, the conservation of momentum principle is at work. For example, when a baseball collides with the baseball bat, the sum of the initial momenta and sum of the final momenta of bat and ball, remain the same. Whatever, momentum the bat loses, the baseball gains.

When a bullet is shot from a gun, the gun recoils, so that sum of bullet's momentum and the gun's momentum in the opposite direction, cancel out and the final momentum and initial momentum of the system is equalized. One simple device that explains the conservation of momentum is 'Newton's Cradle'. It consists of individually hung beads stacked against each other. If you dislodge one bead from one side and release it, it collides with rest of the beads and dislodges one bead from the other side to conserve momentum.
Hope this helps.
Thanking you
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