Introduction to Momentum & Impulse If inertia is a property of motion, then momentum is a quantity of motion. Momentum is a measurement of an object’s motion. It is a vector quantity (magnitude and direction) and it is found as the product of an objects mass and velocity. In physics, we use the letter “p” to denote momentum: ! ! where: -p is momentum (Ns, kg m/s) p = mv -m is mass in kg -v is velocity in m/s Unit Analysis: € The momentum of an object will point in the same direction as its velocity. Eg. 1. A transport truck (m = 4.0x103 kg) and a pickup truck (m = 1.5x103 kg) are both traveling at 36.5 m/s on Hwy 401. Which one has more momentum? Transport Truck Pickup Truck Even though the two trucks are moving at the same speed, the transport truck has a larger momentum due to its larger mass. Impulse Impulse as the rate of change of momentum over time (like acceleration is the rate of change of velocity over time). Impulse can be derived using N2L:

Energy & Momentum: Note 5 We use the letter J for the change of momentum (impulse): J = FΔt where: -J is impulse (Ns, kg m/s) -F is Force in N -t is time in s € Eg. 2. A hockey player slams into the boards with an impulse of 1000.0 Ns over a time of 0.2 s. What force did the boards supply to stop him? Quite often, we must remember what impulse is (the change of momentum). This means that for a particular object moving at a constant speed, the amount of impulse needed to stop IS CONSTANT. When the hockey player hits the boards, J is constant. This means that is t changes, F must also change to compensate for t. As t increases, F decreases to get the same value for J As t decreases, F increases to get the same value for J Alternate Equation From the derivation, we can also get: J = Δp = mv 2 − mv1 FΔt = mv 2 − mv1 This form of the equation can be used if we want to compare initial and final velocities € of an object as its momentum changes. € In Summary ! ! Momentum: p = mv J = FΔt Impulse: J = mv2 − mv1 €

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