Lesson Plan

State what it means for a quantity to be conserved and define an isolated system as one with zero net external force

Explain why momentum that appears not conserved for a single object is conserved once the system is expanded

Derive the conservation of momentum for two colliding objects from the impulse-momentum theorem and Newton's third law

State the law of conservation of momentum verbally and mathematically (p_tot = constant; p_tot = p'_tot)

Describe angular momentum as the rotational analog of linear momentum and explain the figure-skater effect using its conservation

8.2

"To say that a quantity is conserved means that it is constant throughout the event. In the case of conservation of momentum, the total momentum in the system remains the same before and after the collision." "It is always possible to find a larger system where momentum is conserved, even though momentum changes for individual objects within the system." "We know from Newton's third law of motion that F₂ = –F₁, and so $\Delta \vec{p}_2 = -\vec{F}_1, \Delta t = -\Delta \vec{p}_1$. Therefore, the changes in momentum are equal and opposite, and $\Delta \vec{p}_1 + \Delta \vec{p}_2 = 0$." "The law of conservation of momentum states that for an isolated system with any number of objects in it, the total momentum is conserved." "Angular momentum is conserved when the net external torque ($\vec{\tau}$) is zero, just as linear momentum is conserved when the net external force is zero."