Chapter 13: Heat and Temperature Section 1 – Measuring Temperature

Generally, temperature is a measure of how hot or cold something is –Scientifically… Definition: temperature – a measure of the average KE of particles. The particles of ALL matter are constantly moving and vibrating. What is temperature?

If we could look at the atoms & molecules of hot air, we would see… The molecules would be moving very fast! Hot substances have faster moving particles.

What is temperature? If we could look at the atoms & molecules of cold air, we would see… The molecules would be moving very slowly! Cold substances have slow moving particles. Even the particles of ICE are moving…just really slowly.

When the temperature of an object changes, thermal energy is being transferred. Imagine that you are holding a piece of ice in your hand. What happens to the ice? The ice melts, of course, but what happens in scientific terms…?

Your hand is much warmer than the ice. That means that it has more kinetic energy. As you hold the ice in your hand, thermal energy is transferred from your hand to the ice.

As a result, the molecules in the ice move faster… And their kinetic energy increases, which causes the ice to melt. –Definition: heat – the energy transferred between objects with different temperatures. Temperature & Energy Transfer

Thermal energy always flows from hot to cold. “Things that are hot, flow to where it is not.”

Measuring Temperature Definition: thermometer – a device used to measure the temperature of an object. In a typical thermometer, a liquid expands when heated and contracts when cooled. –The level of the liquid can be read to find the temperature.

Temperature Scales In the United States, the Fahrenheit scale is used to measure temperature. –The physicist Daniel Gabriel Fahrenheit developed the scale in Today, only a few countries still use the Fahrenheit scale.

Temperature Scales In 1742, Anders Celsius created the Celsius temperature scale. –The scale uses 0 as the freezing point of water and 100 as the boiling point. –Celsius is used most commonly throughout the world as a means for measuring temperature.

Temperature Scales In 1848, physicist William Kelvin created the Kelvin temperature scale based on “absolute zero”. –Definition: absolute zero – the theoretical temperature at which matter has 0 KE. It is the coldest temperature possible. –Kelvin (K) is the SI unit for temp. It doesn’t use negatives! This makes it perfect for calculations. Absolute zero is -273 degrees Celsius. Or -459 degrees Fahrenheit….BRRR.

Chapter 13: Heat & Temperature Section 2: Energy Transfer Conduction Convection Radiation

Definition: thermal conduction – thermal energy transfer between objects in direct contact. –It occurs as fast moving particles collide with slower moving particles.

For example…have you ever left a metal spoon in a pot on the stove? –When you touched the spoon again, it was likely very hot! –The solid spoon received energy from the stove by conduction.

Some materials can transmit energy better than others. Definition: thermal conductor – a substance that easily transmits thermal energy. Most metals are very good conductors of thermal energy.

Other materials do not conduct thermal energy very well at all. Definition: thermal insulator – a substance that does not transmit thermal energy well. Some examples of insulators: –Glass –Wood –Rubber –Cloth

Definition: convection – the transfer of thermal energy through moving fluids. Convection occurs in the atmosphere, and also in the ocean. It even occurs in our bodies.

Convection currents are “rivers” of moving fluids due to temperature differences. They transmit warmer/cooler air throughout your home. Convection Currents

The oceans also contain convection currents!

Definition: radiation – thermal energy transferred as electromagnetic waves. (Radiant Energy) –Sunlight and infrared waves are examples of radiation.

–Radiation does not require matter in order to transmit energy. When you are near an oven, you can feel the heat of the oven without touching it. This is an energy transfer due to radiation. –Radiation is the only type of energy transfer that can occur through space.

I can haz radeashun?

Chapter 13: Heat & Temperature Section 3: Using Heat

How heat is related to living things? Our bodies maintain a constant temperature of 98.6 ºF. –It takes energy to keep a body at this temperature! So, where does the energy come from? Using Heat: Biology

Remember that food is an example of chemical energy? The body converts chemical PE into thermal energy in order to keep a constant temperature. –The blood flow in your body transports heat to different areas, through convection. Via the circulatory system… Using Heat: Biology

If the body is exposed to cold conditions for too long, it will lose more thermal energy than it produces. –Hypothermia occurs when your body temp. falls below normal. Coooold…

If the body’s temperature rises above normal, it experiences fever. –If it gets too hot, the body can overheat, causing organs to shut down. Fever

Sweat is produced in order to cool the body through evaporation. –The skin becomes covered with sweat… –It absorbs thermal energy from our body, and evaporates… –Leaving our body cooler in the process! Internal Air Conditioning

One of the major uses of heat is air conditioning! –Definition: air conditioning system - a machine used to transfer thermal energy into or out of an area. Heat & Technology

Ever wondered how a refrigerator works? Definition: refrigerant – a substance that is used to cool an area by evaporation. –A refrigerant can easily absorb thermal energy and evaporate. Refrigerants Refrigerators use refrigerants in order to cool the inside.

–A refrigerant absorbs thermal energy in order to evaporate. –Evaporation causes the air to cool. Refrigerators

Heat engines are our major source of travel…what is a heat engine? –Definition: heat engine – a device that converts chemical PE into thermal energy, then into mechanical energy. Heat Engines Internal Combustion Engine