Question 1

What is the Q=mcΔT formula used for?

Accepted Answer

Q=mcΔT (also written Q=mcΔθ) calculates the heat energy transferred to or from an object. Q is heat in joules, m is mass in kg, c is the specific heat capacity in J/kg·K, and ΔT is the temperature change in °C or K. It applies whenever no phase change occurs — heating water, cooling metal, warming air.

Question 2

What is Fourier's law of heat conduction?

Accepted Answer

Fourier's law states that the heat conduction rate Q̇ = k·A·ΔT/L, where k is thermal conductivity (W/m·K), A is the cross-sectional area (m²), ΔT is the temperature difference across the material (°C), and L is the thickness (m). Higher k means the material conducts heat more readily — metals have k of 50–400, while insulation has k of 0.02–0.05.

Question 3

What is Newton's law of cooling?

Accepted Answer

Newton's law of cooling states that the temperature of an object approaches its environment exponentially: T(t) = T_env + (T₀ − T_env) × e^(−kt), where T₀ is the initial temperature, T_env is the ambient temperature, k is the cooling constant (s⁻¹), and t is time. The half-life (time to cool halfway to ambient) is ln(2)/k.

Question 4

What is an R-value and how is it calculated?

Accepted Answer

R-value measures thermal resistance — how well a material resists heat flow. In SI units: R = L/k (m²·K/W), where L is thickness and k is thermal conductivity. Imperial R-value (ft²·°F·h/BTU) = SI R-value × 5.678. US building codes typically require R-13 minimum for exterior walls and R-38 for attics.

Question 5

What is the difference between R-value and U-value?

Accepted Answer

R-value measures resistance to heat flow — higher is better for insulation. U-value (W/m²·K) is the reciprocal: U = 1/R = k/L. A low U-value means better insulation. Windows are often rated by U-value rather than R-value. For a wall with multiple layers, R-values add together while U-values must be combined as reciprocals.

Question 6

What is the specific heat capacity of water?

Accepted Answer

Water has an unusually high specific heat capacity of approximately 4,186 J/kg·K (4.186 kJ/kg·°C or 1 BTU/lb·°F). This means it takes 4,186 joules to raise 1 kg of water by 1°C. Water's high specific heat is why oceans moderate climate and why water-based cooling systems are so effective.

Material	k (W/m·K)	Category	Notes
Aerogel	0.015	Insulation	Best insulator available
Styrofoam (EPS)	0.040	Insulation	Common rigid insulation board
Glass Wool	0.040	Insulation	Fiberglass batt insulation
Air (still)	0.024	Gas	At 25°C, 1 atm
Wood (Pine)	0.12	Building	Varies with moisture content
Brick	0.72	Building	Common fired clay brick
Concrete	1.40	Building	Normal weight concrete
Glass	1.00	Building	Soda-lime window glass
Ice	2.20	Natural	At 0°C
Granite	2.90	Natural	Common igneous rock
Water (25°C)	0.591	Liquid	Liquid water at room temp
Steel (Carbon)	50	Metal	Common structural steel
Aluminum	205	Metal	Pure aluminum alloy
Copper	385	Metal	Excellent thermal conductor
Diamond	1000	Exotic	Highest known thermal conductor

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