AP Physics 1 · AP Physics 1 CED (2024-25) · 18 min read
1. Work and the Work-Energy Theorem★★☆☆☆⏱ 3 min
Energy is a conserved scalar quantity that describes a system's capacity to do work, measured in joules (J, equivalent to $N \cdot m$). Energy topics make up 12-18% of your total AP Physics 1 exam score, appearing in both multiple-choice and free-response questions.
W = F\Delta x \cos\theta
W_{net} = \Delta KE = KE_{final} - KE_{initial}
2. Kinetic and Gravitational Potential Energy★★☆☆☆⏱ 3 min
Energy relevant to AP Physics 1 falls into two broad categories: kinetic energy (energy of motion) and potential energy (stored energy due to position or configuration).
KE = \frac{1}{2}mv^2
U_g = mgh
3. Conservation of Mechanical Energy★★★☆☆⏱ 4 min
Mechanical energy $E_{mech}$ is the sum of kinetic and all potential energy in a system. Conservative forces (gravity, spring force) do path-independent work, while non-conservative forces (friction, air resistance, external applied forces) do path-dependent work and dissipate energy as heat or sound.
E_{mech} = KE + U
KE_i + U_i + W_{nonconservative} = KE_f + U_f
4. Average and Instantaneous Power★★★☆☆⏱ 3 min
Power is the rate at which work is done or energy is transferred between systems, measured in watts (W, equivalent to J/s).
Spring (elastic) potential energy is energy stored in a stretched or compressed spring, relative to its unstretched equilibrium position. From Hooke's Law, the restoring force of a spring is:
F_s = -kx
Where $k$ is the spring constant (stiffness, units N/m) and $x$ is displacement from equilibrium. The negative sign indicates the force acts opposite to displacement to return the spring to equilibrium.
U_s = \frac{1}{2}kx^2
6. Concept Check★★★☆☆⏱ 4 min
Common Pitfalls
Why: Students carry over angle conventions from force component questions.
Why: Students default to ground level as $h=0$ even if the system never reaches the ground.
Why: Students overgeneralize the conservation rule after practicing only frictionless problems.
Why: Students confuse stretch/compression with total spring length.
Why: Students carry over the negative sign from Hooke's Law force calculations.