# Momentum

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• Momentum
• p=mv
• p is momentum (kgms-1)
• m is mass (kg)
• v is velocity (ms-1)
• Newtons laws
• 1st: an object remains at rest or at a constant velocity unless acted on by an external force
• in a vacuum, no friction or gravity
• 2nd: the rate of change of momentum of an object is proportional to the resultant force acting upon it
• F=ma
• F is force (kgms-2)
• m is mass (kg)
• a is acceleration (ms-2)
• ?p= m?v
• F=  ?p/t
• Impulse = F ?t = ?p
• 3rd: for every actions, there is an equal and opposite reaction
• Conservation
• total momentum of a system must remain constant
• provided no external forced act upon it
• m(a)v(a) + m(b)v(b) = 0
• therefore,  m(b)v(b) = - m(a)v(a)
• Impact forces
• F=mv/t
• momentum / contact time
• rebound impacts ?p = (-mv) -(mu)
• F= mv-mu / t
• Conservation
• total momentum of a system must remain constant
• provided no external forced act upon it
• m(a)v(a) + m(b)v(b) = 0
• therefore,  m(b)v(b) = - m(a)v(a)
• Elastic and Inelastic Collisions
• Perfectly Elastic
• all momentum conserved
• all Ek conserved
• relative speed of approach = relative speed of separation
• Perfectly Inelastic
• momentum conserved
• Ek not conserved
• Things stick together
• General Inelastic
• momentum conserved
• Ek not conserved
• no ability to comment on afterwards speed unless calculation done
• Explosions
• recoil with equal and opposite momentum
• use of conservation of momentum