# Force and Momentum

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• Force and Momentum
• Momentum and Impulse
• Momentum = mass x velocity
• An object stays at rest or constant speed unless acted on by another object
• Force = mv -mu / t
• F = ma
• Initial momentum = mu
• Final momentum = mv
• Impulse = change in (mv)
• Impulse = Force x time
• Impact Force
• If the direction of momentum changes, the sign (+ or -) changes
• Impact force = gain of momentum / contact time
• Gain / change of momentum = mv-mu
• Force = mv - mu / t
• Conservation of momentum
• The principle of conservation of momentum states the total momentum remains constant, provided no external resultant force acts on the system.
• Every action has an equal and opposite reaction.
• Force = Change in momentum / time
• (M1V1 = M2V2) -> This is the conservation of momentum
• Elastic and inelastic collisions
• An elastic collision is one where there is no loss of kinetic energy
• An inelastic collision occurs where the colliding objects have less kinetic energy after the collision than before the collision
• Total energy is always conserved, but kinetic energy may be transferred into other energy stores.
• Using the conservation of momentum, if we know both the masses of the colliding objects and one of their velocities, we can work out the other velocity using; mv = m1v1
• Explosions
• When two objects get fired away from each other when initially being at rest they recoil from each other with equal and opposite momentums
• If you use the conservation of momentum for this chapter then you will be fine.
• Remember that energy can be transferred to heat, sound, light or chemical energy.
• Impact Force
• If the direction of momentum changes, the sign (+ or -) changes
• Impact force = gain of momentum / contact time
• Gain / change of momentum = mv-mu
• Force = mv - mu / t