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What is Temperature?. Take 5 minutes to talk to your lab partner. Answer the following questions What is temperature? How do you decide what temperature something is? How hot is hot? How cold is cold?
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What is Temperature? • Take 5 minutes to talk to your lab partner. Answer the following questions • What is temperature? • How do you decide what temperature something is? • How hot is hot? How cold is cold? • When we say something is hot or cold, is that a qualitative measure or a quantitative measure? • When we say something is 50 degrees Celsius is that a qualitative measure or a quantitative measure?
Kinetic Energy • Temperature is the measure of the average kinetic energy of particles. • Temperature is NOT a measure of heat. • We already know that kinetic energy is another way to talk about the amount of movement of particles. SO…. • Higher temperature = More kinetic energy
How Do Thermometers Work? • Liquid thermometers work because of thermal expansion. Thermal expansion is the increase of volume of a substance due to an increase in temperature. • Many thermometers use either mercury or alcohol because they remain in the liquid form over a large range of temperatures.
How Do Thermometers Work? • When a thermometer is placed in hot water bath, heat energy transfers from the hot water bath to the thermometer. The temperature reading on the thermometer rises. It continues to rise until the kinetic energy of the particles in the thermometer match the kinetic energy of the particles in the hot water.
Who invented the thermometer? Galileo- in 1596
Thermal EnergyHeat Transfer Thermal energy is the internal energy in substances. It is vibration and movement of atoms and molecules within substances.
Convection • the transfer of heat (thermal energy) by the actual movement of the warmed matter. It most frequently occurs in gases or liquids. • Heat leaves the coffee cup as the currents of steam and air rise. • The heat moves with the fluid.
Consider This • Convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser.
Conduction • the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. It is most effective in solids-but it can happen in fluids. • It is simplythe transfer of thermal energy through direct contact. • For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon.
Fun Fact • Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.
What do they have in common? Do these items look familiar?
What do they have in common? • All the items in the previous slide are insulators. An insulator is a substance that does not conduct thermal energy well and reduces the amount of heat transfer. • Substances that DO conduct thermal energy well are called conductors. • Take a few minutes to brainstorm a lists some common (household) conductors and insulators with your lab partner…
Radiation • Electromagnetic waves that directly transport ENERGY through space. • Sunlight is a form of radiation. The thermal energy of the sun is radiated through space to our planet without the aid of fluids or solids. The energy travels through nothingness! • Just think of it! The sun transfers heat through 93 million miles of space.
How do we know it’s radiation? BECAUSE….. • There are no solids (like a huge spoon) touching the sun and our planet, conduction is not responsible for bringing heat to Earth. • Since there are no fluids (like air and water) in space, convection is not responsible for transferring the heat.
How a radiometer works • Heat excites the black surface of the vanes more than it heats the white surface. Black absorbs more thermal energy it is considered a good radiator. • The difference in temperature between the warm, black side and the cooler white side causes gasses to creep along the surface of the vanes. This effect is known as "thermal creep." The faster gasses from the black side strike the edges of the vane at an angle with more force than the molecules from the cold side. The equal and opposite forces cause the radiometer to spin.
