Laws of Motion and Momentum

• An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force

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• Velocity is a vector quantity, so an object's velocity changes if its speed and/ or direction changes

• When two objects interact, they exert equal and opposite forces on each other

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• The forces acting on the interacting objects are always of the same type

• Gravitational
• Electromagnetic
• Strong nuclear
• Weak nuclear

p (momentum) = m (mass) * v (velocity)

For a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

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Total momentum before = total momentum after

A gun recoils when a bullet is fired

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The momentum of the gun and the momentum of the bullet have the same magnitude but act in oppsite directions

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The total momentum of the closed system remains the same and is equal to zero

• Momentum conserved
• Total energy conserved 
• Total kinetic energy conserved

• Momentum conserved
• Total energy conserved
• Total kinetic energy not conserved

• The net force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction

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• F (net force) = Δp (change in momentum) / Δt (time)

F = Δp / Δt

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F = (mv - mu) / t

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F = m ((v-u) / t)

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F = ma

According to Newton's third law of motion, each object experiences an equal but opposite force

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The net force acting on the objects in this closed system is zero

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According to Newton's second law of motion, Δp / Δt = 0

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The change in momentum of both objects must be zero

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The total momentum of the objects does not change

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Momentum is always conserved

• The product of force and the time for which this force acts on an object

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• Change in momentum

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• The area under a force-time graph