Temperature and Heat

 The temperature of boiling water is 100º on the Celsius scale and 212º on the Fahrenheit scale.  Look at the following temperatures and guess whether they are hot or cold  60º F  60ºC  37º F  37ºC  0 ºC  100 º F  70 º F

Temperature  Temperature is a measure of how hot or cold something is; specifically, a measure of the average kinetic energy of the particles in an object.

Temperature and Kinetic Energy  All matter is made of atoms or molecules that are always moving, even if you cannot see it.  The motion of the particles means they have kinetic energy.  The faster the particles are moving, the more kinetic energy they have

Demonstration  Take 3 buckets and fill one with cold water, one with warm water, and one with hot water.  Place your hands in the warm water first.  then place one hand in the cold, and one hand in the hot  After a minute, take both hands out and place them in the warm water.  How does the temperature feel on your hands?

Measuring Temperature What can you use to measure temperature? What units are used to measure temperature?

Measuring temperature- Fahrenheit  In the United States we refer to temperature using the Fahrenheit scale (F).  Freezing is 32º F  Boiling point of water is 212º F

Measuring temperature- Celsius  Used in the rest of the world  0º C is freezing  100º is boiling

Measuring Temperature- Kelvin  The Kelvin scale is used by many scientist  273 K is freezing  373 K is boiling point  The lowest temperature on the Kelvin Scale is 0 K which is called absolute Zero

Absolute Zero  Absolute zero is the temperature in which molecular energy is at a minimum  0 Kelvin is absolute zero  -273º C is the absolute zero in Celsius

Thermometers  Many thermometers are thin glass tubes filled with liquid mercury or alcohol.  Mercury and alcohol are often used because they stay in a liquid form at most temperatures.  Thermometers can measure temperature because of thermal expansion.

Thermal Expansion  Thermal expansion is an increase in the size of a substance in response to an increase in the temperature of the substance.  As a substance’s temperature increases, its particles move faster and spread out making an increase in size.

Thermal Expansion Example  Have you ever noticed when you drive on a bridge there are gaps between the road that cause the “thunk- thunk” sound  These are called expansion joints  If the weather is hot, the metal expansion joints can heat up and expand.  Without the expansion joints, the bridge would not be able to expand and would break.

Review!!

______________ is the measure of how hot or cold something is.  A. Thermometer  B. Temperature  C. Conductor  D. Elevator

What temperature scale does the United State use?  A. Fahrenheit  B. Celsius  C. Kelvin  D. Meters

What is the boiling point on the Fahrenheit scale?  A. 0º  B. 100º  C. 212º  D. 32º

What is the freezing point on the Celsius Scale?  A. 100º  B. 0º  C. 273  D. 32º

What is freezing on the Kelvin Scale?  A. 0  B. 273  C. 212  D. 32

What is freezing temperature on the Fahrenheit scale?  A. 32º  B. 100º  C. 0º  D. 212 º

What is the boiling point on a Celsius scale?  A. 32º  B. 100º  C. 0º  D. 212 º

What is the temperature in which molecular energy is at a minimum?  A. Boiling point  B. Absolute Zero  C. Freezing point  D. Celsius

________________is an increase in the size of a substance in response to an increase in the temperature of the substance.  A. Absolute Zero  B. Temperature  C. Thermal Expansion  D. Kinetic energy

What do bridges use to help with thermal expansion?  A. Temperature regulation  B. Expansion Joints  C. Absolute Zero  D. thermometers

Heat

 You are lying in a park. Your eyes are closed and you feel the warmth of the sun on your face. You may have done this before, but have you ever stopped to think that it takes a little more than 8 minutes for the energy that warms your face to travel from a star that is 149,000,000 km away.

Heat Transfer How does the energy move from a hotter to a colder object? Three ways (mechanisms) 1. Conduction 2. Convection 3.Radiation

Conduction  If you ever touched something hot, you have experienced conduction  Thermal conduction is the transfer of thermal energy though a material.  Thermal energy is transferred from warm to cold

Conduction  Transferred through solids.  One molecule is heated and begins to move and shake quickly- it passes some of its heat energy to other molecules around it.  All the molecules of an object pass heat from one to another until they are all hot.

 Hot goes to Cold  Metals are good conductors  Wood and plastic don’t have loosely bound electrons, so they are poor conductors Conduction

Convection  Have you ever watched a pot of water boil, you have observed convection.  Convection is the transfer of thermal energy by circulation or movement of a liquid or gas.

Convection  heated molecules move from one place to another, taking the heat with them  Heated air expands, becoming less dense. Because it is less dense, it rises upward.  Cooler air rushes in to replace the air that lifted up.  As warm air rises and cool air falls, a circular pattern is created.  Hot goes to cold

Convection

Convection  Explains why breezes come from the ocean in the day and from the land at night

Radiation  The earth receives energy from the sun by radiation

Radiation  Energy carried by electromagnetic waves  Light, microwaves, radio waves, x- rays  Wavelength is related to vibration frequency

Radiation  Every object is emitting electromagnetic waves  Things we can see from their own radiation are very hot to have energy emitted in the visible region of the spectrum  Most things emit primarily in the infrared  Night vision goggles, etc.

Radiation radiation

Review  Check this out... Check this out...

Radiation

Convection

Conduction

Conduction

Convection

Radiation

Convection

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Convection

The greenhouse effect  About 70% of the radiation that enters Earth’s atmosphere is absorbed by clouds and the Earth’s surface which is converted into thermal energy that warms Earth.  The atmosphere is a warm blanket that traps enough energy to make Earth livable.

The Greenhouse effect  The greenhouse effect is the warming of the surface and lower atmosphere of Earth that occurs when water vapor, carbon dioxide, and other gases absorb and reradiate thermal energy.

Greenhouse Gases  Many scientists have hypothesized may be the cause of global warming.  Greenhouse gasses are gasses that that absorb thermal energy in the atmosphere.  Human activities such as using of fossil fuels (gas, energy) and cutting down forest may be causing an increase in greenhouse gasses and deforestation.

Review!!

Conduction moves from _________ to _______  A. warm to cold  B. cold to warm  C. high to low  D. low to high

Transfer of thermal energy through a material is______.  A. Convection  B. Conduction  C. Global warming  D. Greenhouse gas

What are the three mechanisms of heat transfer?  1.  2.  3.

Conduction is transferred through ______.  A. Gases  B. liquids  C. Solids

________ are good conductors  A. plastic  B. Glass  C. Metal

What is the transfer of thermal energy by circulation or movement of a liquid or gas?  A. Conduction  B. Convection  C. Global warming  D. Heat.

Heated air rises______  A. Upward  B. Downward  C. laterally  D. stays where it is

________ is a transfer of energy as electromagnetic waves.  A. Radiation  B. Conduction  C. Convection  D. Heat

An example of radiation…

Night vision goggles help you see ________.  A. Heat  B. Conduction  C. Radiation