Lesson Plan

Define linear momentum, state that it is a vector with the same direction as velocity, and calculate it from p = mv

Express Newton's second law in terms of momentum (F_net = Δp/Δt) and derive the familiar F = ma as the constant-mass special case

Define impulse and state the impulse-momentum theorem (Δp = F_net·Δt)

Explain how extending the time of impact reduces force, and apply this to safety features such as airbags and crumple zones

Solve problems using the impulse-momentum theorem to find momentum, change in momentum, or average force

8.1

"Linear momentum is the product of a system's mass and its velocity. In equation form, linear momentum p is $\vec{p} = m\vec{v}$." "Newton actually stated his second law of motion in terms of momentum: The net external force equals the change in momentum of a system divided by the time over which it changes." "$\vec{F}_\text{net}, \Delta t$ is known as impulse and this equation is known as the impulse-momentum theorem. From the equation, we see that the impulse equals the average net external force multiplied by the time this force acts. It is equal to the change in momentum." "Airbags allow the net force on the occupants in the car to act over a much longer time when there is a sudden stop. The momentum change is the same for an occupant whether an airbag is deployed or not. But the force that brings the occupant to a stop will be much less if it acts over a larger time."