Thermal Physics Notes PDF - States of Matter, Brownian Motion, Conduction

UNIT 2: THERMAL PHYSICS Co-ordinated Science (0654)  LESSON TOPIC: STATES OF MATTER Fact: "Matter exists in different states depending on temperature and pressure."  LESSON OBJECTIVES Identify the distinguishing pro...

UNIT 2: THERMAL PHYSICS Co-ordinated Science (0654)  LESSON TOPIC: STATES OF MATTER Fact: "Matter exists in different states depending on temperature and pressure."  LESSON OBJECTIVES Identify the distinguishing properties of 1. solids, liquids, and gases. Define terms for changes in state (melting, boiling, 2. evaporation, condensation). Compare the arrangement and motion of particles 3. in solids, liquids, and gases using diagrams.  PROPERTIES OF SOLIDS, LIQUIDS, AND GASES Property Solid Liquid Gas Takes container’s Shape Fixed No fixed shape shape Volume Fixed Fixed No fixed volume Slightly Highly Compressibility Incompressible compressible compressible Flow Does not flow Flows easily Flows freely Matter makes up everything! CHANGES OF STATE PARTICLE ARRANGEMENT AND MOTION https://youtu.be/ixNoDpD02WU  QUIZ 1.Which state of matter has a fixed shape and volume? 2.Define evaporation. 3.Sketch the arrangement of particles in a gas. 1. Solid: Solids have a fixed shape and a fixed volume because their particles are tightly packed in a regular arrangement and vibrate in place. 2. Evaporation: It is the process by which a liquid changes into a gas at the surface of the liquid, occurring at temperatures below its boiling point. 3. In a gas, particles are far apart, randomly arranged, and move freely at high speeds.  LT: PARTICLE MODEL Objectives 1. Describe how particle motion relates to temperature. 2. Explain Brownian motion as evidence for the kinetic particle model. 3. Relate gas pressure to particle collisions with surfaces.  WHAT HAPPENS TO THE PARTICLES WHEN TEMPERATURE INCREASES? When an object is heated, the average kinetic energy of the particles in the object increases and the particles move or vibrate faster. When an object is cooled, the average kinetic energy of the particles in the object decreases and the particles move more slowly. The lowest temperature where the particles have the least kinetic energy occurs at –273°C. This temperature is also known as absolute zero.  BROWNIAN MOTION Brownian motion refers to the random movement of microscopic particles in a fluid due to the collisions by the molecules of the fluid. Examples of microscopic particles are pollen grains and smoke particles.  HOW DOES BROWNIAN MOTION OCCUR? There are millions of molecules in the air moving at high speeds in all directions. This means that there are many collisions on each smoke particle happening all the time. The smoke particle is constantly pushed one way and then another. As we cannot see the molecules, the smoke particles appear to be constantly moving small distances in a random path. https://youtu.be/gPMVaAnij88  HOW DO GASES EXERT A PRESSURE? The gas particles are moving randomly in all directions. They collide with one another and with the walls of the container. The pressure on the container is caused by the constant collisions of many particles with its walls. When the particles collide with the walls of the container, they exert a force on the wall. What do you think will happen to the pressure of the gas in the container if the temperature is increased Pressure is force per unit area. Hence, the but the volume stays the same? force exerted by the collisions of gas particles on the container gives rise to the pressure on the container.  LT: PARTICLE MODEL Objectives 1. Describe the effect of temperature on gas pressure at constant volume. 2. Explain the effect of volume changes on gas pressure at constant temperature. 3. Solve simple qualitative problems involving gas laws. https://youtu.be/oc8hmUuvC48 HOW DOES THE PRESSURE OF A GAS VARY WITH ITS TEMPERATURE?  HOW DOES THE PRESSURE OF A GAS VARY WITH ITS TEMPERATURE? For a fixed volume and mass of gas, increasing its temperature results in an increase in the speeds of the gas particles. This increases the rate at which the particles collide with the walls of the container. What do you think will happen to the pressure of the gas in the container if the volume Pressure–temperature graph of is increased but the temperature is constant? a gas at constant volume  HOW DOES THE PRESSURE OF A GAS VARY WITH ITS VOLUME? Have you noticed how bubbles in a fish tank increase in size as they rise from the bottom of the tank to the top? Do you know why this happens?  HOW DOES THE PRESSURE OF A GAS VARY WITH ITS VOLUME? For a fixed mass of gas at constant temperature, a decrease in volume results in particles having less space to move in. Hence, this increases the rate at which particles collide with the walls of the container. The gas pressure of a fixed mass of gas at constant temperature increases when the volume decreases. The amount of space that the particles can move in decreases as volume decreases.  EXAMPLE A gas cylinder contains 600 ml of carbon dioxide at a pressure of 2 × 107 Pa. Assuming that the temperature of the gas does not change, calculate the volume of the gas at atmospheric pressure, 1 × 105 Pa.  QUIZ 1. Using the kinetic particle model of matter, explain a) how the air particles in a container exert pressure on the walls of the container; Gas particles move at high speeds and collide with each other and with the walls of the container. Each time a gas particle collides with the container wall, it exerts a small force/area on the wall. The cumulative effect of all these collisions results in pressure being exerted on the walls of the container. a) why the pressure of the air increases as the temperature increases. 2. (a) Describe how the pressure of a gas changes with volume when the temperature of the gas is constant. (b) Give the equation for the relationship between pressure and volume of a gas when the temperature of the gas is constant. p1V1 = p2V2  LESSON TOPIC: THERMAL EXPANSION Bridges expand in hot weather and contract in cold weather.  LESSON OBJECTIVES 1. Describe thermal expansion in solids, liquids, and gases. Explain everyday applications of thermal expansion. 2. Analyze consequences of thermal expansion in structures and 3. systems.  WHAT HAPPENS WHEN MATERIALS ARE HEATED? Solids, liquids and gases increase in volume or expand when heated. The greater the temperature rise, the greater the expansion. When cooled, the volume will decrease, i.e., it will contract. Liquids expand more than solids for the same temperature rise. This is the principle behind liquid-in glass thermometers. Gases expand much more than liquids.  WHY DO SOLIDS, LIQUIDS AND GASES EXPAND BY DIFFERENT AMOUNTS? Heating materials gives the particles more kinetic energy. In solids, the particles vibrate more vigorously. Strong forces between them results in a small expansion. In liquids, the particles move around faster. The forces between the particles are weaker as compared to solids, so the expansion is greater. Gas particles move about the fastest as compared to solid and liquid particles. Gases have the greatest expansion because there is little force between the particles.  WHAT ARE THE APPLICATIONS AND CONSEQUENCES OF EXPANSION? If there is no space to expand, large forces may act. Engineers must take expansion into account when designing structures. RAILWAY LINES Some railway lines have expansion gaps to allow for expansion when the lines get hot. Modern railway lines do not have gaps. The lines are designed to fit tightly on a hot day. On cold days, the lines contract, but they are still held in place by supporting structures underneath. BRIDGES Bridges also expand and contract with changes in temperature. Top figure shows an expansion gap at one end of a concrete bridge. Another way of allowing for expansion is to put one end of the bridge on rollers. SHRINK FITTING Expansion can be used to fix two metal parts together using shrink fitting. An example is fitting a metal axle into a metal train wheel. The metal axle is first made too large for the hole in the metal train wheel. Then, the axle is cooled to shrink so it will fit into the wheel. When the axle warms up and expands, the two metals are firmly held together.  QUIZ 1. What evidence is there that the forces caused by expansion are large? 2. Explain why overhead telephone wires hang more loosely on a hot day. 3. Explain using the kinetic particle model of matter why solids contract when they are cooled.  LESSON TOPIC: CHANGE OF STATE  LESSON OBJECTIVES 1. Identify melting and boiling points of water in Celsius. 2. Differentiate between boiling and evaporation. Explain evaporation in terms of particle motion and energy 3. transfer. WHAT HAPPENS TO THE TEMPERATURE WHEN MATERIALS CHANGE STATE? You can find out using the apparatus shown in what happens to the temperature of a substance when it changes state. WHAT HAPPENS TO THE TEMPERATURE WHEN MATERIALS CHANGE STATE? From A to B, the thermal energy is being taken in to raise the temperature. From B to C, the temperature remains constant at 0°C. The thermal energy is being taken in to change state. From C to D, the thermal energy is being taken in to increase the temperature. From D to E, the thermal energy is being taken in to change state. WHY IS ENERGY NEEDED WHEN A SUBSTANCE CHANGES ITS STATE? During melting: The particles in a solid are held in fixed positions by strong bonds. When the bonds are weaken, the particles can move out of their fixed positions and are slightly further apart from each other. During boiling: The particles in a liquid have strong forces between them. Energy is needed to break the bonds and separate the particles further apart. Energy is also required for the particles to overcome the atmospheric pressure in order to escape into the air.  COOLING A SUBSTANCE During Condensation: During condensation, a gas turns into a liquid as it loses heat. The particles in the gas slow down and move closer together, forming a liquid. The temperature stays the same during this process because the heat energy being removed is used to change the state, not to lower the temperature. During Solidification: During this phase change, the temperature remains constant (the graph shows a flat line between D and E) because the energy being lost is used to form the rigid structure of a solid. WHAT IS EVAPORATION? Factors affecting evaporation: 1. Temperature 2. Surface area of the liquid 3. Movement of air DIFFERENCES BETWEEN EVAPORATION AND BOILING EXAM-STYLE QUIZ  HOMEWORK QUIZ 1. Explain why energy is needed to turn a solid into a liquid. 2. Explain why puddles evaporate more quickly on a warm day than a cold day. 3. Give two factors that make wet clothes on a washing line dry more quickly. 4. Give one similarity and one difference between evaporation and boiling.  LESSON TOPIC: EVAPORATION AND COOLING  LESSON OBJECTIVES Describe evaporation as escape of energetic particles from a liquid 1. surface. Explain factors affecting evaporation, such as surface area and air 2. movement. 3. Understand that evaporation causes cooling of the liquid.  WHAT IS EVAPORATION? At the surface of a liquid, a few molecules gain enough kinetic energy to overcome the intermolecular forces surrounding it and escape as a gas. This process is evaporation. Note that evaporation is a superficial process – it only occurs on the surfaces of liquids.  EVAPORATION CAUSES COOLING When you step out of a swimming pool on a windy day, you feel cold. Why? This is because the water is evaporating from your skin surface, which results in a decrease in temperature.  EVAPORATION CAUSES COOLING During evaporation, the most energetic molecules escape into the atmosphere, carrying away their energy with them. This means there is less total energy left in the liquid. As temperature is a measure of the average kinetic energy of the liquid, and there is less kinetic energy, thus, the liquid cools. GUIDED READING LT: CONDUCTION  LESSON OBJECTIVES 1. Identify good and bad thermal conductors and insulators. Describe conduction in solids using particle vibrations and 2. delocalized electrons. 3. Explain applications of thermal conduction in everyday contexts.  HOW GOOD ARE DIFFERENT MATERIALS AT CONDUCTING THERMAL ENERGY? Conduction is the transfer of heat from one region to another through particle vibrations and the movement of free electrons. Conduction is the main method of thermal energy transfer in solids. Demonstration of conductivity in metals HOW GOOD ARE DIFFERENT MATERIALS AT CONDUCTING THERMAL ENERGY? Materials that can transfer thermal energy quickly are good thermal conductors. Bad thermal conductors are also known as thermal insulators. HOW DOES CONDUCTION WORK? HOW DOES CONDUCTION WORK? APPLIC ATIONS OF THERMAL CONDUCTION IN EVERYDAY CONTEXTS QUESTIONS? LT: CONVECTION  LESSON OBJECTIVES 1. Define convection as energy transfer in liquids and gases. 2. Describe convection currents and their formation. 3. Explain density changes driving convection currents.  HOW DO LIQUIDS AND GASES TRANSFER THERMAL ENERGY? Convection is the transfer of thermal energy in a fluid (liquid or gas) by means of convection currents due to a difference in density.  CONVECTION IN LIQUIDS Convection currents form because of the difference in density in water when heated. When the water at the bottom of the flask is heated, it expands. The expanded water is less dense than the surrounding water. The warmer, less dense water rises. The colder, denser water sinks to replace the risen water. This process repeats until the whole flask of water is heated up.  CONVECTION IN GASES Convection currents form because of the difference in density in air when heated. When the air above the candle is heated, it expands. As the warm air is less dense than the surrounding air, it rises out of the right chimney. Cooler denser air sinks down the left chimney to take the place left by the warm air, carrying the smoke from the incense stick along. https://youtu.be/Ht1NmwlWaCo QUESTIONS? LT: APPLICATIONS OF CONVECTION https://youtu.be/8pEHimrJA-A  LESSON OBJECTIVES 1. Identify real-world examples of convection processes. Explain how convection influences weather patterns and home 2. heating. 3. Design a simple experiment to demonstrate convection currents.  REAL-WORLD EXAMPLES OF CONVECTION 1.Boiling Water: Hot water rises, cools at the surface, and sinks. 2. Weather Systems: Warm air rises at the equator, cools, and sinks at the poles. Creates global wind patterns (e.g., trade winds). Influences cloud formation and precipitation. 3. Home Heating: Radiators or heaters warm the air nearby. Warm air rises, cools, and sinks, creating a convection current. Ensures even heating in a room. 4. Ocean Currents: Warm water moves from the equator to the poles. REAL-WORLD EXAMPLES OF CONVECTION REAL-WORLD EXAMPLES OF CONVECTION  QUICK QUIZ 1. What causes convection currents? 2. How does convection affect weather? 3. Why does warm air rise?