Physics Concepts: Heat, Energy, and Thermodynamics

Posted on Dec 5, 2024 in Physics

Heat, Energy, and Thermodynamics

Heat and Energy

1 cal = 4.18 J
1 J = 0.24 cal
Q = m * c_e * (t_f – t_i)
Q_gained + Q_lost = 0
Q = m * L (Latent Heat)

Thermal Expansion

Cubic Expansion: β * V * Δt
β (cubic expansion coefficient)
V = initial volume
Δt = temperature increase
Superficial Dilatation: γ * S * Δt
γ (coefficient of superficial dilatation)
S = Initial surface area
Δt = temperature increase
Linear Expansion: α * L * Δt
α (linear expansion coefficient)
L = original length
Δt = temperature increase

Work and Power

Work: W = F * d
W = P * t
Unit: Joule
Power: P = W / t
Unit: Watt
1 C.V. = 736 W
1 kWh = 3,600,000 J

Energy

Kinetic Energy: KE = (1/2) * m * v²
Potential Energy: PE = m * g * h
Mechanical Energy: E_m = E_c + E_p = constant (Principle of Conservation of Energy)
Work-Energy Theorem: W = ΔE_c = (1/2 * m * v²) – (1/2 * m * v₀²)
Change in Kinetic Energy: ΔE_c = E_cf – E_ci

Definitions

• Work: Product of force and displacement times the cosine of the angle between them.
• Joule: Work done when a force of 1 N produces a displacement of 1 m.
• Watt: Power applied when performing work of 1 Joule per second.
• Power: Measures the rate at which work is done.
• Energy: The ability of a body to do work.
• Mechanical Energy: Sum of kinetic and potential energy.
• Theorem of Live Forces: Total work done by forces acting on a body equals the change in its kinetic energy.
• Kinetic Energy: Energy a body possesses due to its motion.
• Potential Energy: Energy stored in a body due to its position in a force field (gravitational, electrical, elastic, etc.).
• Conservation of Mechanical Energy: In the absence of friction, mechanical energy remains constant.

Kinetic Theory of Gases

Gases are made of tiny particles in continuous, random motion. The volume occupied by the particles is negligible compared to the container’s volume. Particles continuously collide without losing kinetic energy. Pressure is proportional to the number of collisions with the container walls. Particles are separated, so forces are negligible except during collisions. Not all particles have the same speed. Average kinetic energy is proportional to absolute temperature.

Kinetic-Molecular Theory of Matter

Solids: Particles have limited motion, vibrating around equilibrium positions. Heating increases vibration until particles break free (fusion) at the melting point.
Liquids: Particles have more freedom due to weaker cohesive forces.
Evaporation: Faster liquid particles overcome cohesion and escape to the gas phase, cooling the liquid.
Boiling: Occurs throughout the liquid at a specific temperature (boiling point), where most cohesive forces are overcome.
Phase Changes:
Solid → Gas: Sublimation
Solid → Liquid: Fusion
Liquid → Gas: Vaporization (boiling or evaporation)
Gas → Liquid: Liquefaction
Liquid → Solid: Solidification
Gas → Solid: Deposition

Temperature and Heat

Temperature: Proportional to the average kinetic energy of particles. Measured in Kelvin (K) or Celsius (°C).
Heat: Energy transferred between bodies at different temperatures. Measured in Joules (J) or calories (cal).

Calorimetry

Specific Heat (c_e): Energy needed to raise the temperature of 1 kg of a substance by 1 K.
Calorimeter: Thermally insulated container.
Thermal Equilibrium: When two bodies at different temperatures reach the same temperature in a calorimeter.

Latent Heat

Energy required for a phase change at constant temperature.