Physical Science - Heat & Matter - Summers, S

Physical Science Overview

• Focus: Thermodynamics

• Emphasis on the laws governing heat and energy transfer.

The Nature of Heat

• Historically viewed as a substance called caloric.

  • Caloric: weightless, invisible, odorless, tasteless.

  • Heating: absorbing caloric increases temperature; losing caloric decreases temperature.

• Key Contributors:

  • Count Rumford: Early ideas placing heat as energy.

  • James Prescott Joule: Demonstrated that heat is energy.

What is Heat?

• Defined as internal energy of matter: sum of energies of all atoms/molecules.

• Change in energy can be achieved through heat transfer.

• Units of Measurement:

  • SI unit: Joule (J).

  • British Thermal Unit (Btu): Energy required to raise 1 lb. of water by 1°F. (1 Btu = 1.054 kJ).

Direction of Heat Transfer

• Heat defined as energy transferred between bodies of different temperatures.

  • Flows from higher to lower temperature.

• Internal energy of a system changes through heat transfer.

What is Temperature?

• Temperature relates to the sensation of "hot" or "cold."

• More precisely, it is related to average motion of molecules.

• Temperature and heat are different properties; confusion should be avoided.

Measuring Temperature

• Thermometer used to measure temperature.

• Properties used in measurement:

  • Thermal expansion: volume increases with temperature.

  • Color and light emission: color changes from red to white with increased temperature.

Temperature Scales

• Common scales in the U.S.:

  • Fahrenheit scale: (F = \frac{9}{5}C + 32)

  • Celsius scale: (C = \frac{5}{9}(F - 32))

  • Kelvin scale: Absolute temperature scale without negative values.

Heat Transfer Mechanisms

• Conduction: Heat transferred by molecular collisions.

• Convection: Heat carried by moving fluids.

• Radiation: Heat transferred via electromagnetic waves.

Archimedes’ Principle

• States that the buoyant force on an object in a fluid equals the weight of fluid displaced.

• Density determines whether an object floats or sinks:

  • Floats if density < fluid’s.

  • Sinks if density > fluid’s.

• Natural convection also discussed.

Changing Temperature

• Specific Heat Capacity: Energy needed to change 1 kg of a substance by 1°C.

  • Formula: (Q = c\Delta T) (where Q = heat added/removed, c = specific heat, (ΔT = ) change in temperature).

States of Matter

• Solid: Definite volume and shape.

• Liquid: Definite volume, shape conforms to the container.

• Gas: Neither definite volume nor shape, fills the container.

  • Liquids and gases collectively termed fluids.

Changing the Phase of Matter

• Latent heat: Energy exchange is required for phase changes (e.g., solid to liquid).

• Temperature does not change during phase transitions.

Heat of Vaporization

• Energy needed to convert 1 kg of a substance from liquid to gas at its boiling point.

• Equal amount of heat released when gas condenses back to liquid.

Heat of Fusion

• Energy required to melt 1 kg of solid at its melting point.

• Equal heat released when liquid solidifies.

Some Heats of Fusion and Vaporization

• Includes data for various substances such as Copper, Ethanol, Lead, Mercury, Nitrogen, Oxygen, and Water, detailing melting and boiling points along with their heat attributes.

Pressure

• Defined as force acting per unit area: (p = \frac{F}{A})

• SI Unit: Pascal (Pa); conversions to kPa and lb/in² discussed.

Pressure in Fluids

• Fluid pressure acts perpendicularly to surfaces.

• Forces within a fluid exerted uniformly at a given depth.

The Gaseous State of Matter

• Governed by several gas laws (Boyle's Law, Charles’s Law).

• Understanding the Ideal Gas Law provides insight into gas behavior with changing conditions.

Boyle's Law

• Relates pressure and volume: (P_1V_1 = P_2V_2)

Absolute Temperature

• Absolute zero: -273°C (theoretical lowest temperature).

• Temperatures expressed as Kelvin (K) are above absolute zero (no negatives).

Charles's Law

• Connects volume and temperature; relationship established for gases:

  • (\frac{V_1}{T_1} = \frac{V_2}{T_2})

Other Gas Laws

• Brief mention of Gay-Lussac's Law and Avogadro's Law, along with implications for gas behavior.

Ideal Gas Law

• Formulated as (PV = nRT); connects pressure, volume, number of moles, and temperature.

Kinetic Theory of Gases

• Describes molecular behavior in gases:

  1. Gas molecules are small compared to distances apart.

  2. Collisions do not lose kinetic energy.

  3. Minimal forces between molecules except during collisions.

  4. Absolute temperature correlates to average kinetic energy.

  • Gases consist primarily of empty space.

Solids and Fluids

• Comparison of particle behavior in solids, liquids, and gases.

Thermodynamics Basics

• Study of heat transformations.

  • First Law: Energy cannot be created/destroyed; it can only change forms.

  • Second Law: Not all heat can be converted into work; some will always be wasted.

Heat Engines

• Devices that convert thermal energy to mechanical energy; operate under the principles of heat flow from hot to cold.

• Refrigerators work inversely, moving heat from cold to hot regions.

Examples & Applications

• Several real-world problems and calculations related to temperature conversions, buoyant forces, heat transfer calculations, and gas laws are provided with solutions (e.g., body temperature conversion, air mass determination, buoyant force calculations).