Mechanics · Momentum
Chapter 1 · 4
The idea
Linear momentum
Linear momentum p = mv as a vector quantity in one dimension — how the sign carries the direction of motion, how to combine the momenta of several particles, and how to find a change in momentum by working with velocities (with signs) rather than speeds.
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Mechanics · Momentum
Linear momentum
Linear momentum p = mv as a vector quantity in one dimension — how the sign carries the direction of motion, how to combine the momenta of several particles, and how to find a change in momentum by working with velocities (with signs) rather than speeds.
Why it works
Mass times velocity — with a sign
The linear momentum of a particle is the product of its mass and its velocity: Mass is measured in kilograms and velocity in metres per second, so momentum has units of (equivalently ). Because velocity is a vector, momentum is a vector too — in one dimension that means the sign of records the direction of motion.Choose a positive direction first
In this course all momentum problems are in a straight line, so before writing anything down, decide which way counts as positive. A particle moving the other way then has a negative velocity, and therefore a negative momentum. This single habit — velocities carry signs, speeds do not — is what makes momentum calculations come out right.Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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