Connection: Give me the definition of temperature. Why does temperature involve mass and speed of particles?
temperature and heat
Temperature and Heat
All Matter is Made of Moving Particles• All moving objects have kinetic energy• Objects such as a house or a wooden chair have kinetic energy because atoms are constantly in motion, even if the objects are not changing position
The Kinetic Theory of Matter• The Kinetic Theory of Matter states that all of the particles that make up matter are constantly in motion. – The particles in a solid are not free to move around very much. They vibrate back and forth and are held tightly together by the forces of attraction. – The particles in a liquid move more freely then a solid. They are sliding around and tumbling over each other.. – The particles in a gas are far apart and move around at high speeds. Particles might collide with one another, but otherwise they do not interact much.
Temperature and Kinetic Energy• Temperature is a measure of the average kinetic energy of all the particles in an object
Temperature and Kinetic Energy• If a liquid has a high temperature, particles in the liquid are moving very fast/have a high average kinetic energy• If a liquid has a low temperature, particles are moving more slowly/have a lower average kinetic energy
Temperature and Kinetic Energy• Temperature depends on both mass and speed of particles.• Particles in a metal doorknob do not move as fast as particles in the air; however, the particles in a doorknob have more mass than air particles. Therefore, they can both have the same temperature.
Temperature Scales• Fahrenheit• Celsius• Kelvin
Fahrenheit Scale• Develop in early 1700s by G. David Fahrenheit• Zero is the lowest temperature that salt water will freeze• 32° F is freezing point of pure water• 212° F is boiling point of pure water• F scale used in US for surface temperatures
Celsius Scale• Developed in 1700s• Also called Centigrade scale• Zero is the freezing point of pure water• 100 is the boiling point of pure water at sea level• A change of 1 C° = 1.8F°• 1.8 C = F -32
Kelvin Scale• Absolute zero – molecules stop moving• Lowest possible temperatures• Zero K = -459° F• Zero K = -273° C• °K = °C + 273• Kelvin scale used for all scientific equations
Thermometers• A thermometer measures temperature through the variation of some physical property of material inside the thermometer• Ex: a mercury or alcohol thermometer can measure temperature because the liquid inside the thermometer always expands or contracts by a certain amount in response to a change in temperature
Thermal Expansion• The property that makes a liquid-filled thermometer work is called thermal expansion.• All solids, liquids and gases expand when their temperature increases• Construction engineers often have to take thermal expansion into account because steel and concrete both expand with increasing temperature
Thermal Expansion• The Gateway Arch in St. Louis is built mostly of steel.• The final piece of the Arch to be put into place was the top segment joining the two legs• The workers sprayed water on the side facing the Sun to to reduce thermal expansion.• Once the final segment was in place, engineers made the connection strong enough to withstand the force of the expanding material
Heat is Different than Temperature• Heat is the flow of energy from an object at a higher temperature to an object at a lower temperature• Thermal Energy is the total kinetic energy of the molecules• Temperature is the average kinetic energy of the molecules
Measuring Heat• One calorie is the amount of energy needed to raise temperature of 1 g of water by 1° C• This means that 1000 calories of food is enough energy to 1 kilogram of water 1°C
Measuring Heat• The joule (J) is the standard scientific unit in which energy is measured.• 1 Calorie = 4.18 joules
Specific Heat• The amount of energy required to raise the temperature of 1 gram of a substance by 1°C is the specific heat of that substance.• Every substance has its own specific heat – 1 Calorie raises the temperature of 1 g of water by 1° C – 0.108 Calories raise the temperature of 1 g of water by 1°C
Specific Heat and Mass• Recall that thermal energy is the total kinetic energy of all particles in an object• Thermal energy depends on the object’s mass• Water in a glass has the same specific heat as water in a bathtub• If the water in the bathtub and coffee cup are the same temperature, the bathtub will have to release more thermal energy because of its mass
Specific Heat and Mass: Application• This idea is particularly relevant for large masses• For example, Lake Michigan holds 4.92 quadrillion liters of water.• Because of the high specific heat of water and the mass of the water in the lake, the temperature changes very slowly
Specific Heat and Mass: Application• The temperature of the lake affects the temperatures on its shores• During spring and early summer, the lake warms slowly, which helps the nearby land stay cooler• During the winter, the lake cools slowly which helps keep the nearby land warmer• Temperatures within about 15 miles of the lake can differ about 6°C (10° F)
Energy Moves As Heat in Three Ways• Recall that heat is always a transfer of energy of objects at a high temperature to an object of a lower temperature
Conduction• Conduction is the process that moves energy from one object to another when they are touching physically• Conduction happens any time objects at different temperatures come into contact with each other• As long as objects are in contact, conductions continues until the temperatures are equal
Conduction• Conductors are materials that transfer energy easily.• Conductors often have a low specific heat (metals are generally good conductors)• A metal pot becomes too hot to touch soon after the pot is placed on a stove that has been turned on
Conduction• Other materials, called insulators, are poor conductors.• Insulators have high specific heat.• Examples: Wood, paper, plastic• A plastic foam cup will not easily transfer energy by conduction; therefore, they are often used to keep cold drinks cold or hot drinks hot.
Convection• Convection is the process that transfers energy by the movement of large particles in the same direction within a liquid or gas.• Convection occurs when a cooler, denser mass of the gas or liquid replaces a warmer, less dense mass of the gas or liquid by pushing it upward.
Convection• Convection is a cycle in nature responsible for most winds and ocean currents. When the temperature of a region of air increases the particles in the air spread out and the air becomes less dense. – Cooler, denser air flows underneath the warmer, less dense air, and pushes the warmer air upward – When this air cools it becomes more dense than the warmer air beneath it – The cooled air sinks and moves under the warmer air
Radiation• Radiation is energy that travels as electromagnetic waves, which include visible light, microwaves and infrared light.• The sun is the most significant source of radiation that you experience on a daily basis; however, all objects, even you, emit radiation and release energy to their surroundings
Different Materials Are Used to Control the Transfer of Energy• Energy is always being transferred between objects are different temperatures• It is often important to slow this movement of energy• Think-Pair-Share: Think of one situation where it would be important to slow the movement of energy.