# 5.4 Measuring Thermal (Internal) Energy The amount of energy in an object depends on: 1.Mass of the object 2.Temperature of the object 3.The nature of.

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5.4 Measuring Thermal (Internal) Energy The amount of energy in an object depends on: 1.Mass of the object 2.Temperature of the object 3.The nature of the material of the object

Specific Heat Capacity Different materials have different capacities for holding thermal energy

Specific Heat Capacity The amount of heat needed to raise the temperature of 1 kg of a substance by 1 ˚ C

Specific Heat Capacity The amount of heat needed to raise the temperature of 1 kg of a substance by 1 ˚ C

Specific Heat Capacity The amount of heat needed to raise the temperature of 1 kg of a substance by 1 ˚ C

Specific Heat Capacity The amount of heat needed to raise the temperature of 1 kg of a substance by 1 ˚ C

If 25 kJ of heat is transferred to 50.0 kg of water initially at 20.0˚C, what will be the final temperature of water?

HOMEWORK Textbook: Page 161 Problems: 5.4.1 8

The rate of thermal conduction depends on the substance The metal tray feels colder than the package because metal conducts energy more easily and more rapidly than cardboard does.

Thermal Conductors Substances that rapidly transfer energy as heat In general, metals are good thermal conductors.

Substances that slowly transfer energy as heat Materials such as asbestos, cork, ceramic, cardboard, and fibreglass are poor thermal conductors (and therefore good thermal insulators). Thermal Insulators

Heat Transfer by Convection Involves the movement of cold and hot matter, such as hot air or hot water

Heat Transfer by Convection Thermal energy is not easily transferred by CONDUCTION in fluids (liquids and gases)

Heat Transfer by Convection The thermal energy “flows” with a particle from one place to another as a substance is being heated = the thermal energy is being carried around

Heat Transfer by Convection This movement is called a CONVECTION CURRENT

Convection in Everyday Life

another way that heat can be transmitted occurs where energy CAN’T be transferred by CONDUCTION or CONVECTION

Heat Transfer by Radiation Energy transmitted via RADIATION will be in the form of ELECTROMANETIC WAVES and will travel at the SPEED OF LIGHT

Heat Transfer by Radiation The various forms of RADIANT ENERGY (which originate in the SUN)

Convection in Everyday Life

SOLAR FURNACE

HOMEWORK Textbook: Page 154 Problems: Quick Check 23

HOMEWORK Textbook: Page 159 Problems: all 26

WORKSHEET EXAMPLE A 6.0 kg cat runs after a mouse at 10m/s. What is the cat’s kinetic energy? KE = 300 J

WORKSHEET EXAMPLE How much net work is needed to accelerate a 1000.0 kg car from 20.0 m/s to 30.0 m/s

Can You Have a Negative PE? You could bring a textbook from a table height to a zero – level (ground) – performing a negative work If yes, give an example If not, explain why.

Can you have an object with a positive PE relative to one point and negative PE to another point at the same time? A textbook which is 1.0 m below a table (negative PE relative to the table) If yes, give an example If not, explain why. A textbook which is 1.0 m above the ground (positive PE relative to the table)

WHAT IS THE UNIT OF k? N/m

WORKSHEET EXAMPLE When a 2.00 kg mass is attached to a vertical spring, the spring is stretched 10.0 cm such that the mass is 50.0 cm above the table. a.What is the gravitational potential energy associated with this mass relative to the table? b.What is the spring’s elastic potential energy if the spring constant is 400.0 N/m ? c.What is the total potential energy of this system?

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