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Visual Review
AP Physics 2 Unit 1 Visual ReviewA topic-by-topic visual walkthrough of Unit 1: Thermodynamics — kinetic theory, the ideal gas law, heat transfer, the first and second laws, specific heat, and entropy.
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TOPIC 1.1
Kinetic Theory: Temperature & Pressure
Temperature = average kinetic energy
KE_avg = (3/2) k_B T
The average translational KE of a gas
molecule is proportional to ABSOLUTE T.
T must be in KELVIN. k_B = 1.38×10⁻²³ J/K
v_rms = √(3k_B T / m) — hotter = faster molecules
molecules collide with the walls → pressure
Pressure comes from wall collisions
Countless molecules striking the container walls exert a force per unit area — that's the gas PRESSURE (P = F/A).
KE_avg = (3/2)k_B T (T in kelvin); pressure = molecular collisions on the walls.The Review Hub · AP Physics 2 · Unit 1
TOPIC 1.2
The Ideal Gas Law
PV = nRT = N k_B T
The symbols
P = pressure (Pa), V = volume (m³)
n = moles, R = 8.31 J/(mol·K)
N = number of molecules, T in KELVIN
Relates the state variables of a gas.
at fixed n,T: P₁V₁ = P₂V₂ (Boyle's law)
Worked example
2 mol of gas at 300 K in 0.05 m³:
P = nRT/V
= (2)(8.31)(300)/0.05
≈ 9.97×10⁴ Pa
Always convert temperature to kelvin first.
PV = nRT = Nk_B T relates pressure, volume, amount, and (kelvin) temperature.The Review Hub · AP Physics 2 · Unit 1
TOPIC 1.3
Thermal Energy Transfer
Conduction
Direct contact —
molecule to molecule.
metal spoon in soup
Metals conduct well;
air/wood insulate.
Convection
Bulk motion of a
fluid carries heat.
warm air rising
Warmer fluid is less
dense → it rises.
Radiation
Electromagnetic waves —
no medium needed.
heat from the Sun
Every warm object
radiates (see 1.5).
Heat flows from hot to cold until equilibrium
Two objects in contact reach THERMAL EQUILIBRIUM when they have the same temperature — net heat flow stops.
Heat transfers by conduction, convection, radiation — hot to cold until equilibrium.
The Review Hub · AP Physics 2 · Unit 1
TOPIC 1.4
The First Law of Thermodynamics
ΔU = Q + W (W = work done ON the gas)
|W| = area under the P–V curve
P V
Signs & processes
Q > 0: heat ADDED · W > 0: gas COMPRESSED.
W = −P·ΔV (constant pressure)
ISOTHERMAL: ΔU = 0 → Q = −W.
ADIABATIC: Q = 0 → ΔU = W.
ISOCHORIC (ΔV=0): W = 0 → ΔU = Q.
First law: ΔU = Q + W (energy conservation); |W| = area under the P–V curve.
The Review Hub · AP Physics 2 · Unit 1
TOPIC 1.5
Specific Heat & Thermal Conductivity
Heating a substance
Q = m c ΔT
c = specific heat (J/kg·K) — energy to
raise 1 kg by 1 K.
Water's c is large (4186) → resists
temperature change.
Worked example
Heat 0.5 kg of water by 20 K:
Q = (0.5)(4186)(20)
= 41,860 J ≈ 42 kJ
Conduction rate through a slab:
P = kA·ΔT / L
Thermal conductivity k
The rate of conduction rises with the material's conductivity k, the area A, and ΔT — and falls with thickness L.
Q = mcΔT ; conduction rate P = kA·ΔT/L.The Review Hub · AP Physics 2 · Unit 1
TOPIC 1.6
Entropy & the Second Law
Second law: the entropy of an ISOLATED system never decreases
ΔS ≥ 0 · systems evolve toward more disorder / probable states
Entropy = disorder
Entropy S measures how spread out
energy & matter are.
Heat flowing hot→cold, gas expanding,
and mixing all INCREASE entropy.
A local decrease requires a bigger increase elsewhere.
Heat engines can't be perfect
No engine converts heat to work with
100% efficiency — some heat is always
rejected to a cold reservoir.
efficiency e = W / Q_hot < 1
This is a direct consequence of the second law.
Second law: total entropy never decreases (ΔS ≥ 0) ; no engine is 100% efficient.
The Review Hub · AP Physics 2 · Unit 1
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How to use the visual review
Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"
Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.
This is great for review the night before the exam — fast, visual, and covers everything you need to remember about Unit 1's thermodynamics.