Lesson Plan

Explain how mechanical energy transforms between potential and kinetic forms

State the law of conservation of energy and explain what a "closed system" means

Apply the conservation equation KE₁ + PE₁ = KE₂ + PE₂ to solve for an unknown energy or speed

Calculate gravitational potential energy as mgh and kinetic energy as ½mv² at points in a process

Use the mass-cancellation shortcut (2gh = v²) to find landing speeds without knowing the mass

Identify friction as the reason real transformations lose useful energy as heat

9.2

"We saw earlier that mechanical energy can be either potential or kinetic. In this section we will see how energy is transformed from one of these forms to the other. We will also see that, in a closed system, the sum of these forms of energy remains constant." "At any point in the ride, the total mechanical energy is the same, and it is equal to the energy the car had at the top of the first rise. This is a result of the law of conservation of energy, which says that, in a closed system, total energy is conserved—that is, it is constant. ... $$KE_1 + PE_1 = KE_2 + PE_2.$$" "The phrase in a closed system means we are assuming no energy is lost to the surroundings due to friction and air resistance."