* Defining Temperature * We associate temperature with how hot or cold an object feels. * Our sense of touch serves as a qualitative indicator of temperature. * Energy must be either added or removed from an object to change its temperature. * Temperature is proportional to the kinetic energy of atoms and molecules. * Temperature is a measure of the average kinetic energy of the particles in a substance. * A substance temperature increases as a direct result of added energy being distributed among the particles of a substance. * Internal energy is the energy of a substance due to both the random motions of its particles and to the potential energy that results from the distances and alignments between the particles. 1
* Temperature is proportional to the kinetic energy of atoms and molecules. * The internal energy of a material is due to the random motions of its component particles and is equal to the total energy of those motions. * The particles can be atoms or molecules, and they can have three forms of energy: translational, rotational, and vibrational.. * Translational energy is energy that comes from the horizontal or vertical motion of particles. * Rotational Energy is energy that comes from the rotation or spinning of the particle. * Vibrational energy is energy that comes from the bending or stretching of the bonds within the particles. * Kinds of Energy Visual Concept 2
* Thermal expansion * In general, if the temperature of a substance increases, so does its volume. This phenomenon is known as thermal expansion. * Different substances undergo different amounts of expansion for a given temperature change. * The thermal expansion characteristics of a material are indicated by a quantity called the coefficient of volume expansion. * Gases have the largest values for this coefficient. Solids typically have the smallest values. * Thermal expansion * In general, when the temperature of a material increases its volume also increases, regardless of whether the material is a solid, liquid, or gas. Visual Concept 3
* Thermal expansion * In general, the volume of a liquid tends to decrease with decrease temperature. * However, the volume of water increases with decreasing temperature in the range between 0 C and 4 C. * When water freezes, crystal form which have more empty space between the molecules than the liquid. This explains why ice floats in liquid water. * Solids typically have the smallest coefficient of volume expansion values. For this reason, liquids in a solid container expand more than the container. This property allows some liquids to be used to measure changes in temperature. * Measuring Temperature * Temperature is measured in one of three common temperature scales: * Celsius Degrees * Fahrenheit Degrees * Kelvin * To have a temperature scale we need to know the values for: * The freezing point of pure water * The boiling point of pure water * The number of units between them. * DEGREE is a unit between 2 points in a temperature scale. 4
* Fahrenheit Scale * Most commonly used in the USA * Developed in the early 1700 s by Gabriel Fahrenheit. * Pure water freezes at 32 F * Pure water boils at 212 F * There are 180 equal units or degrees between the freezing point and boiling point. * Celsius Scale * Most commonly used in the rest of the world * Developed in 1740 by Andre Celsius * Pure water freezes at 0 C * Pure water boils at 100 C * There are 100 equal units or degrees between the freezing point and boiling point. 5
* Kelvin * Most commonly used in the scientific world. * Pure water freezes at 273 K * Pure water boils at 373 K * There are 100 equal units between the freezing point and boiling point. * Kelvin scale of temperature does not use the suffix degrees. * Kelvin scale is referred to as the absolute scale. * The 0 temperature in the Kelvin Scale is referred to as the absolute zero. * Measuring Temperature * In order for a device to be used as a thermometer, it must make use of a change in some physical property that corresponds to changes in temperature, such as the volume of a gas or liquid, or the pressure of a gas at a constant volume. * The most common thermometers use a glass tube containing a thin column of mercury, colored alcohol, or colored mineral spirits. * When the thermometer is heated, the volume of the liquid expands. * The change in length of the liquid column is proportional to the temperature. 6
* Changes in temperature * Matter exists in one of three states: * solid * liquid * gas * Matter can change from one state to another when there is a change in the kinetic energy or temperature of the object. * Melting occurs when a solid becomes a liquid. * The melting point is the point at which melting begins. * Melting begins when the particles of a solid start vibrating fast enough so that they start breaking away from one another and become a liquid. * Changes in temperature * Freezing occurs when a liquid turns into a solid. * The freezing point is the point at which freezing begins. * At the freezing point, a liquid particle loses energy. They don t move as quickly and eventually become a solid. * The melting point and the freezing point of a substance are the same. * Above the freezing / melting point, the substance is a liquid. * Below the freezing / melting point, the substance is a solid. * At the freezing / melting point, the substance can be either a liquid or a solid. * The freezing / melting point of water is 0 C Above Below 15 C Water is liquid 0 C Water is neither solid nor liquid -15 C Water is solid (ice) 7
* Changes in temperature * Evaporation is the process by which a liquid becomes a gas. * Particles in liquids move at different speeds. The fastest moving particles escape from the surface of a liquid becoming gas. * Since warmer liquids have faster moving particles, evaporation occurs more quickly when a substance is warmer. * Boiling is another process that allows a liquid to become a gas. * When heated, particles within a liquid from bubbles of gas. When these bubbles of gas start moving fast enough they rise to the surface of the liquid and escape. * The boiling point is the point at which a boiling can occur. * Evaporation can occur at many temperatures, but boiling can occur only at or above the boiling point. * The boiling point of water is 100 C. * Changes in temperature * The boiling point of water is 100 C. * The boiling point of water changes with altitude, because there is less pressure at higher altitudes, bubbles in the water vapor need less energy to escape from a liquid. Less Pressure 3000 meters Water boils at 89 C More Pressure Water boils at 100 C Sea Level 8
.Sublimation Evaporation.Melting.Freezing Condensation Deposition 2/20/2015 * Changes in temperature * Condensation occurs when a gas turns into a liquid. * Condensation, like evaporation occurs at a wide range of temperatures. * Particles in gas move more slowly near a cool surface and may form a liquid at the cooler surface. * Most gases condense when its temperature is reduced below the substances boiling point. * Sublimation occurs when a solid turns directly into a gas without going through a liquid phase. * Dry ice, which is frozen Carbon dioxide (CO 2 ), turns directly into carbon dioxide gas under normal temperature conditions. * Deposition occurs when a gas turns directly into a solid without going through a liquid phase. * Changes in temperature GAS. LIQUID. Boiling point Freezing / Melting point SOLID * Boiling is another way of changing a liquid into a gas. 9
* Changes in temperature * The temperature scales most widely used today are the Fahrenheit, Celsius, and Kelvin scales * Celsius and Fahrenheit temperature measurements can be converted to each other using this equation: * T F = 1.8 T C + 32 * Temperature in Fahrenheit = 1.8 * temperature in Celsius + 32 * The number 32.0 indicates the difference between the ice point value in each scale: 0.0ºC and 32.0ºF * T C = (T F 32 ) / 1.8 * Temperature in Celsius = (temperature in Fahrenheit 32 ) / 1.8 * Changes in temperature * Temperature values in the Celsius and Fahrenheit scales can have positive, negative, or zero values * But because the kinetic energy of the atoms in a substance must be positive, the absolute temperature that is proportional to that energy should be positive also. * A temperature scale with only positive values is suggested by the graph on the next slide. This scale is called the Kelvin scale. 10
* Changes in temperature * A temperature difference of one degree is the same on the Celsius and Kelvin scales. The two scales differ only in the choice of zero point. * Thus, the ice point (0 C) equals 273K, and the steam point (100 C) equals 373K. * The Celsius temperature can therefore be converted to the Kelvin temperature by adding 273. * T K = T C + 273 * Temperature in Kelvin = Temperature in Celsius + 273 * Temperature is a measure of the average kinetic energy of the particles that make up an object. * Heat is a flow of energy from an object at a higher temperature to an object at a lower temperature. * Heat and temperature are not the same thing. * Heat and Thermal Energy * Heat is always the transfer of energy from an object at a higher temperature to an object of lower temperature. * Example: * Water and bowl temp 15 C * Ice cubes temp. 0 C * Bowl temp. 22 C * In time ice will melt and the water and the bowl will have the same temperature. 11
* Heat and Thermal Energy * The water and the bowl end up with the same temperature, which is lower than the original temperature of the bowl, but higher than the original temperature of the ice. * The bowl and the water end up with the same temperature because the particles of the bowl and the ice collide among them, gaining or losing energy. * When the energy flows from one object to another, the thermal energy of both objects changes. * Heat and Thermal Energy * Thermal energy is the total random kinetic energy of particles in an object. * Thermal energy isn t the same as temperature because the total amount of particles in the object s isn t the same. * Example: * More particles of water * Glass of water temp 22 C * Lake Superior temp 22 C * More Thermal energy 12
* Measuring HEAT * The most common units for measuring heat are: * Calorie * Joule * One calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. * Joule is the standard scientific unit in which heat is measured. * One calorie is equal to 4.18 Joules. 1 calorie = 4.18 Joules * In Nutrition Calorie is written with a CAPITAL C, which is actually known as 1 kilocalorie or 1,000 calories. * SPECIFIC HEAT * The Specific heat of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by 1 degree Celsius. * Every substance has its own Specific Heat * The Specific Heat of water is one calorie per gram per Celsius, and since one calorie is equal to 4.18 Joules then we can say that the Specific heat of water is 4.18 Joules per gram C.. 13
* SPECIFIC HEAT * A large value of Specific heat means that the substance must absorb a big amount of energy for it to increase its temperature; and it also means that it must release a big amount of energy to decrease it temperature. * The high Specific Heat of water is the reason why it is used as a coolant in car radiators. * SPECIFIC HEAT and MASS * Thermal energy is the total random kinetic energy an object has, so it depends on the objects mass. * Example: * More mass = more thermal energy * Cup of water temp 90 C * Bath tub with water temp 40 C * The water in the cup will cool faster because it has less mass even though it s hotter than the water in the tub. It will take longer for the tub water to cool because it has more mass. 14
* Heat is transfer of energy from an object at a higher temperature to an object at a lower temperature. * Energy moves heat in three ways: * conduction * convection * radiation * To control energy we must control conduction, convection, and radiation. * CONDUCTION * Conduction is the process by which energy moves from one object to another when they are physically touching. * For conduction to occur:. 1) Objects must be touching 2) Objects must have different temperatures * Conduction will happen until the objects are: 1) Not touching 2) Have the same temperature. * Some materials are better then others to transfer energy (heat). * Conductors are materials that transfer energy (heat) easily. 15
* CONDUCTION * Some materials are better then others to transfer energy (heat). * Conductors are materials that transfer energy (heat) easily. * Conductors have: * Low values of Specific heat * Examples: most metals * Insulators are materials that do NOT transfer energy (heat) easily. * Insulators have: * High values of Specific heat * Examples: wood and plastic. * CONDUCTION 16
* CONVECTION * Convection is the process that transfers energy by the movement of large numbers of particles in the same direction within liquids and gases. * With an increase in energy there is an increase in kinetic energy, particles spread out (thermal expansion). When particles spread out they reduce their density. When the density is reduced a substance goes up. * CONVECTION 1) Warmer less dense air is pushed up by the cooler denser air. 2) As the air cools, it becomes more dense and starts to sink. 3) Sinking air moves under the warmer air, pushing it back up so that the cycle repeats. * Convection in large bodies of water (lakes and oceans) influence the temperature of the nearby land. 17
* CONVECTION * RADIATION * Radiation is the energy that travels as electromagnetic waves.. * Radiation includes: * microwaves * Infrared light * Visible light * The sun is the most significant source of radiation, but all objects emit radiation and release energy. 18
* RADIATION * Radiation from the sun * Transfer to objects and persons * Objects become warmer. * Thermal expansion occurs * Particles move faster. * CONDUCTION CONVECTION & RADIATION * Similarities transfer energy (heat) from warmer objects to cooler objects. * Differences Radiation travels through empty space. 19
* Different materials are used to control the transfer of energy. * Energy is always being transferred between objects that coexist at different temperatures. * Insulators are used to control the flow of energy (heat) because they are poor conductors. * Insulators are the materials that keep cool things cool and hot things hot. * An insulators is an energy trapper, it prevents energy from flowing. * Good insulators include: * Wood * Fiber glass * Plastic * air * Shinny materials that reflect radiation 20