An Introduction to the An Introduction to the Weather UnitWeather Unit

Science 10 PIBScience 10 PIBMarch 18, 2011March 18, 2011

WeatherWeather

• In this unit, we will examine some of the factors that affect weather dynamics.

• We will start by considering energy transfer from the sun because it is this energy that fuels the movements of air and water that result in weather dynamics around the world.

Weather/ ClimateWeather/ Climate

• Q: How would you describe today’s weather?

• Q: How would you describe our climate?

Weather/ClimateWeather/Climate

• Weather – is defined as the set of environmental conditions encountered from day to day.

• Climate – is defined as the set of environmental conditions averaged over a period of many years.

Relationship between Heat and Relationship between Heat and WeatherWeather

• Most weather phenomenon are related to the ways in which the land, water, and atmosphere transfer the heat that comes to earth as a result from the Sun’s UV rays.

• Q: What is the definition of heat?

• Q: What is the definition of temperature?

DefinitionsDefinitions

• Heat – is a form of energy that is transferred from a hot substance to a cooler substance.

• Temperature – is defined as a measure of the average kinetic energy held by the molecules in a substance.

Definitions cont..Definitions cont..

• Heat Capacity – is a term used to describe how difficult it is to heat up or cool down a particular substance.

Important FACT!Important FACT!

• In relation to weather, water has a much higher heat capacity than land. This means that it takes a lot more energy to heat up the same amount of water as it does land.

• It also takes longer to cool water than it does land!

Kinematic TheoryKinematic Theory

• A theory developed to relate heat to the movement of molecules. It states that:– All matter is composed of molecules– Molecules are separated by space. This

separation is large compared to their size.– Molecules are constantly in motion, therefore

possesing energy– Molecules move FASTER as they gain energy

and SLOW down as they lose energy

Heat Transfers!!!Heat Transfers!!!

• Q: What happens when heat is transferred between two substances?

Answer!Answer!

• As the cooler substance absorbs energy, the molecules begin to move more quickly and hit each other more often.

• AKA – The Kinetic Energy (K.E.) is increasing!

K.E. and DensityK.E. and Density

• As the K.E. increases, molecules speed up and hit each other more frequently. This results in a slight increase in volume.

• Since the mass of the object stays the same, and the volume increases, this results in the warmer object having a lower density!

Heat TransferHeat Transfer

• There are three ways in which energy can be moved from one place to another:– 1) Conduction– 2) Convection– 3) Radiation

ConductionConduction

• The transfer of heat from one object to another by DIRECT CONTACT is called conduction.

• Can anyone explain this?

ConductionConduction

• If objects in one section are heated, their K.E. is higher (molecules are moving faster). When this object comes in contact with another, the molecules will in turn collide with the neighboring molecules and increase their K.E.!!

• Most metals are good conductors.Non-metals not so much…

Convection Convection

• When fluids are heated, they gain more K.E. and temperature increases. Molecules move further apart, density decreases.

• The less dense material moves up, while the more dense material drop.

Convection CurrentConvection Current

• This movement of high/low density creates a current.

• Ex. Hot air from your furnace goes to your ceiling. Where does the cold air go?

RadiationRadiation

• For conduction or convection to occur, matter must be present. However, energy from the sun travels to Earth through a vacuum.

• Radiation is the transfer of heat from a hot to cold object in the absence of any kind of matter!

RadiationRadiation

• Q: Can you think of any examples of radiation?

ExamplesExamples

• You can feel radiant heat from a fireplace

• You can feel radiant heat at the beach, from the sun!

• Ever walk on the road in your bare feet during the summer? Radiant energy!

Heat CapacityHeat Capacity

• = the quantity of heat energy required to raise the temp. of one gram of a substance one degree Celcius.

Adding Heat to a SubstanceAdding Heat to a Substance

• When energy is added to a substance, the resulting change in temperature depends on:– The mass of the substance– The amount of energy added in joules– The specific heat capacity of the substance in

joules per gram ºC

Q = mcQ = mc▲T▲T

• Q = quantity of heat energy (j)

• M = mass (g)

• C = heat capacity (J/gºC)

• T = temperature (ºC)

ExampleExample

• What quanity of heat energy is required to warm a 11.3 g sample of granite from 24ºC to 27ºC?? (0.79J/g°C)

RearrangeRearrange

• You may rearrange this equation to determine the change in temperature that a certain amount of water will cause in a given mass of water:

• Δt = Q/ mc

Specific Heat CapacitiesSpecific Heat Capacities

• The specific heat capacity for water will always be 4.18J/gºC

• To determine other heat capacities, refer to your textbook OR the website