Heat Chapter 4 PSC 1515

Kinds of Energy Potential Energy – stored energy Kinetic energy – the energy of motion Energy can be transferred from one form to another but cannot be gained or lost.

Kinetic Theory of Matter Kinetic Energy is the energy of motion. KE = ½ mv2 (mass times velocity squared) Atoms and molecules are always in motion. They can rotate, vibrate or move in straight lines from one place to another Total is called thermal energy Thermal = heat

Temperature vs heat Temperature is the measure of the average kinetic energy of a system. Molecular motion is proportional to the temperature Heat is the movement of air from an area of high temperature to one of low temperature

Measuring Temperature Three scales, Fahrenheit, Celsius, and Kelvins Note: Both Fahrenheit and Celsius use the degree sign (0) but Kelvin does not Fahrenheit Celsius Kelvin FP water 320 00 273.16 Body temp 98.60 37.00 310.16 BP water 2120 1000 373.16

Temperature and Motion At zero Kelvin (-273.160 C) all but some small amount of thermal energy is gone. The molecule can only move in a small internal vibration. Temperature is related to motion so if the molecule cannot move then the temperature must be true zero – Absolute Zero It is said that “At 0 Kelvins, all molecular motion stops.”

Heat Is the flow of thermal energy from an area of high energy to one of low energy. Not the same as temperature which is a measure of molecular motion. Measured in calories or joules (jewels) Calorie = the energy needed to raise the temperature of one gram of water one degree Celsius. -

Specific Heat Calorie is for water Specific heat is same thing applied to all other materials SpH = amount of energy needed to raise the temperature of one gram of substance by 1 degree Celsius Definition tells you that the energy needed is larger for larger samples and for greater temperature changes.

Thermodynamic Laws Thermodynamics – movement of heat 1. The amount of heat lost by the system must equal the amount gained by the surroundings heat lost = -heat gained 2. Heat (thermal energy) always flows from high to low (true of everything in the Universe) 3. You can never reach absolute zero. To make something cold you must use something colder

Entropy – Degree of Disorder Universe moves from high order to low order. (True of every system in the universe) High order is low entropy and vice versa Entropy lost by system is gained by surroundings

Specific Heat of Water Higher than any other naturally occurring compound on Earth = 1 calorie or 4.184 joules Because surface of Earth is 75% water, the ability of water to absorb and hole heat is always one of the major factors in weather

Calculations Check out questions on page 87 Heat = SpH x mass x change in temp

Why does ice float? Things generally expand when they are heated up and contract when they are cold due to molecular motion Density is related to temperature – The lower the temperature the higher the density Water is different from other substances It expands when it forms a solid

Water as a solid Every water molecule in liquid water is attached to about three other water molecules. In a solid, each water molecule is attached to four other water molecules. This makes the water molecules move further apart and less dense

Consider this What would happen to a lake in winter (up North where it freezes) if water behaved like other compounds – the solid is more dense than the liquid?

Heat Transfer: Conduction Conduction – the transfer of heat by the movement of electrons from one atom to another – molecule to molecule transfer – molecules don’t move Metals – defined as good conductors of heat and electricity Nonmetals – not good conductors - insulators

Convection Convection – movement of the fluid itself Warm air rises, Put your hand over the stove burner Compression of air causes it to get hotter Convection causes winds and movement of air around globe – uneven heating of the Earth by the sun

Radiation Radiation – the transfer of heat energy through a vacuum Conduction and convection require a material to move All heated bodies radiate energy – heat seeking goggles and missiles use a body’s radiant energy to find the target.

To Be Continued When we get to chapters 9 and 10 Heat cycle Sun heats ground Ground heats air, Warm air rises and it moves laterally to areas of cooler air It cools as it rises Night comes and sun stops heating