Temperature and heat transfer

What are the two basic ways of changing the temperature of an object?

1. By doing work on the object, such as the work done by the drill on the metal block. 2. By supplying energy to the object, such as mechanical, chemical, or electrical energy.

What is a heat pump?

A device that warms or cools by transferring heat fro a lower-temperature source to a higher temperature source, or vice versa. It is often used for heating in the winter and cooling in the summer.

Why does any friction between two surfaces result in a temperature rise of the materials?

Because the collision of atoms causes them to speed up, in turn creating heat.

How does the ability of water to absorb alot of heat affect the climate of many places?

Cities on large lakes, like Chicago, are warmer in the winter and cooler in the summer near the lake because of the high heat capacity of water. High temperatures in summer and low temperatures in winter in the middle of large continents are largely due to the absence of large bodies of water. Europe is warmer in the winter than mid-Canada because warm air from over the Atlantic Ocean is blown by prevailing westerly winds over the land.

What is vaporization?

The change of phase from a liquid to a gas or vapor.

What is the coefficient of linear expansion?

A constant that is equal to the change in unit length of a solid when its temperature is changed 1 degree

What is the common U.S. temperature scale?

Fahrenheit scale

One of the most progressive countries with regard to geothermal energy production?

Iceland

What is the specific heat of a substance?

It is the measure of its capacity to absorb or give off heat per degree change in temperature. It is the amount of heat necessary to change the temperature of 1 kg of it 1°C (metric) or 1 lb of it 1°F.

What is evaporation?

The process by which high-energy molecules of a liquid continually leave its surface.

How do most solids expand and contract?

They expand and contract in all three dimensions--length, width, and thickness.

Refrigerators and freezers are forms of what?

heat pumps. Heat is transferred from the appliance to the room.

What was Gabriel Daniel Fahrenheit?

physicist, was born in Poland. He invented the alcohol thermometer in 1769 and the mercury thermometer in 1714.

There is not ______________ change during change of phase

temperature

What are the mechanical equivalent of heat formulas?

1. 1cal of heat is produced by 4.19 J of work 2. 1kcal of heat is produced by 4190 J of work 3. 1 Btu of heat is produced by 778 ft lb of work

The rate of evaporation of a liquid depends on what factors?

1. Amount of surface area: The larger the surface area, the greater is the number of molecules that have a chance to escape from the surface. 2. Temperature: The higher the temperature, the higher is the molecular energy of the molecules, which allows more molecules to escape. 3. Surface currents: Air currents blowing over the liquid's surface remove many of the molecules that have evaporated before they fall back into the liquid, which is why a cool summer breeze fells so good. 4. Volatility: the volatility of a liquid is a measure of its ability to vaporize. Examples of highly volatile liquids are rubbing alcohol and gasoline. The more volatile the liquid, the greater is its rate of vaporization. 5. Pressure on or above the liquid: The lower the pressure, the greater is the rate of evaporation. Under a partial vacuum, there are fewer molecules available with which liquid molecules may collide, allowing for a higher rate of escape and a higher rate of evaporation. 6. Humidity: If the liquid is exposed to the atmosphere, lower humidity values will provide for greater evaporation.

Name and describe the three different types of heat transfer.

1. Conduction: Requires the presence of matter. The heat transfer from a warmer part of a substance to a cooler part as a result of molecular collisions, which cause the slow-moving molecules to move faster. Conduction is the usual method of heat transfer in solids. 2. Convection: Requires the presence of matter. The heat transfer by the movement of warm molecules from one region of a gas or a liquid to another. The convection process can be natural or forced. 3. Radiation: does not required the presence of matter. The heat transfer through energy being transmitted in the forms of rays, waves, or particles. Is similar to light and passes through air, glass, and the vacuum of space.

What are three examples in which heat is converted into useful work?

1. In our bodies: When food is oxidized, heat energy is produced, which can be converted into muscular energy, which in turn can be turned into useful work. 2. By burning gases: When a gas is burned, the gas expands and builds up a tremendous pressure that may convert heat to work by exerting a force to move a piston in a cylinder or turn the blades of a turbine. Since the burning of the fuel occurs within the cylinder or turbine, such engines are called internal combustion engines. 3. By steam: Heat from burning oil, coal, or wood, may be used to generate steam. When water changes to steam under normal atmospheric pressure, it expands about 1700 times. When confined to a boiler, the pressure exerts a force against the piston in a steam engine or against the blades of a steam turbine. Since the fuel burns outside the engine, most steam engines or steam turbines are external combustion engines.

The amount that a solid expands depends on what factors?

1. Material: Different materials expand at different rates. Steel expands at a rate less than that of brass. 2. Length of the solid: The longer the solid, the larger is the expansion. A 20 cm steel rod will expand twice as much as a 10 cm steel rod. 3. Amount of the change in temperature: The greater the change in temperature, the greater its expansion.

What are the two absolute zero temperature scales?

1. The Kelvin scale. This is the metric version. 2. The Rankine scale. This is the English version.

What are the four factors that determine the rate at which heat is transferred through an object?

1. The thermal conductivity 2. The cross-sectional area through which the heat flows 3. The thickness of the material 4. The temperature difference between the two sides of the material

Describe how certain properties of matter vary with their temperature.

1. When objects are heated, they give off light of different colors. If we could determine the color of light, we could determine the temperature. Only works for objects heated to high temperatures. 2. When liquids or solids are heated, their volume changes. Example would be alcohol in glass thermometers. The height to which the alcohol raises indicates its temperature.

What are the units of measure of heat in both the English and metric systems?

1. kilocalorie (kcal): The amount of heat necessary to raise the temperature of 1 kg of water from 14.5C° to 15.5C°; however, the variation for each 1°C change in temperature is so minimal that it can be ignored for all practical purposes. 2. Calorie (cal): The amount of heat necessary to raise the temperature of 1 g of water 1°C. Note: one food calorie is the same as 1 kcal. 3. Btu: The amount of heat necessary to raise the temperature to 1 lb of water 1°F.

what is the latent of vaporization for water in calories, kilocalories, kiloJoules, and Btu's?

540 calories to vaporize 1g water 540 kilocalories to vaporize 1kg water 2.26 MJ to vaporize 1 kg water 970 Btu's to vaporize 1 lb of water

How much heat does it require to melt of ice in calories, kilocalories, kiloJoules, and in Btu's?

80 calories to melt 1g 80 kilocaries to melt 1kg 335 kJ to melt 1kg 144 Btu's to melt 1 lb

How does a heat pump work?

A heat pump contains a vapor called a refrigerant that is easily condensed into a liquid when under pressure. The liquid refrigerant gives up the heat gained during compression to the higher temp source. The liquid is then released to a low-pressure part of the heat pump, where it quickly evaporates and takes its heat of vaporization from the lower-temperature heat source. The vapor is then compressed again, and the cycle repeats

What are some advantages of solids expanding?

Bimetallic strips used in thermostats

What is the freezing and boiling point on the Celsius scale?

Freezing point 0°C and boiling point 100°C

What is the freezing and boiling point on the Fahrenheit scale?

Freezing point 32° and boiling point 212°

A decrease in pressure does what to its boiling point? How can this principle be used in technology?

It decreases it/Frozen concentrate orange juice is produced by subjecting the pure juice to very low pressures at which the water in the juice is evaporated. The consumer then restores the lost water at home.

How to automobiles present important problems concerning change of phase?

Most substances contract on solidifying. However, water and a few other substances expand. The tremendous force exerted by this expansion is shown by the number of cracked automobile blocks and burst radiators suffered by careless motorists every winter. Impurities in water tend to lower the freezing point. Alcohol has a lower freezing point than water and is used in some types of antifreeze. By mixing too much water with antifreeze in the cooling system, an unknowing person can raise the freezing point of the coolant, allowing it to freeze an crack the engine block.

Describe how unique water is in its expansion characteristics

Nearly all liquids are the most dense at their lowest temperature before a change of phase to become solids. As the temperature drops, the molecular motion slows and the substance becomes denser. Water does not follow this general rule. Because of its unusual structural characteristics, water is most dense at 4°C or 39.2°F instead of 0°C or 32°F. As ice melts and the water temperature is slightly increased, there are still groups of molecules that have the open crystallographic structure of ice, which is less dense than water. As the water is heated to 4°C, these groupings disappear and the water becomes denser. Above 4°C, water then expands normally as the temperature is raised. This unique behavior of water is critical in the winter time in lakes that freeze in the winter. If, as in most liquids, water were most dense at its freezing point, the coldest water would settle to the bottom and the lake would freeze from the bottom up. Any living think would be killed. Fortunately, the most dense water at 4°C is at the bottom and the less dense water at 0°C is above it, so ice forms at the surface, the water below remains liquid, and the lake freezes from the top down. When ice melts at 0°C or 32°F, the water formed contracts as the temperature is raised to 4°C or 39.2°F. Then it begins to expand, as do most other liquids.

How can the R value be written?

R-value

The insulation value of construction material is often expressed in terms of the _____________ value, which indicates what?

R/its ability to resist the flow of heat and uses U.S. units.

What is geothermal electrcal generation?

Technology where geophysicists drill into the ground to pierce reservoirs of heated water and vapor to harness the pressure of the steam which ultimately drives turbines that create electricity.

What is the difference between temperature and heat?

Temperature is a measure of the hotness or coldness of an object. Heat is the total thermal energy (kinetic and potential) that can be transferred from an object at a higher temperature to one at a lower temperature.

What is the common metric temperature scale?

The Celsius scale.

What is one of the world's largest geothermal power plants?

The Geysers in norther California. It is located on the edge of the North American tectonic plate and comprises a series of geothermal plants.

What is heat of fusion?

The amount of heat required to melt 1g or 1kg or 1 lb of a substance.

What is the latent heat of vaporization?

The amount of heat required to vaporize 1g or 1kg or 1 lb of a liquid.

What is condensation?

The change of phase from a gas to a liquid.

How does evaporation cool your body?

The change of the liquid of your sweat to gas helps to keep your body cool. When you become too warm, your sweat glands produce water, which evaporates from your skin. In a cool summer breeze, the perspiration evaporates more rapidly which cools you faster. On a hot, humid day, you tend to remain hot because the perspiration does not evaporate as quickly.

What happens at 100% saturation of relative humidity?

The dew point is reached which is the temperature at which saturation is reached. As a result, condensation occurs in the form of dew, fog, mist, clouds, and rain or other forms of precipitation.

What is relative humidity?

The ratio of the actual amount of vapor in the atmosphere to the amount of vapor required to reach 100% of saturation at the existing temperature. As the air temperature decreases without change in pressure of vapor content, the relative humidity increases until it reaches 100% at saturation.

What are absolute zero scales?

They are temperature scales called such because 0 refers to the lowest limit of temperature, called absolute zero.

How do digital thermometers work?

They measure the electrical resistance of the metal tip at the end of the thermometer. As the temp of the metal increases, the resistance increases.

What is heat?

a form of internal kinetic and potential energy contained in an object associated with the motion of its atoms or molecules and may be transferred from an object at a higher temperature to one at a lower temperature

What is temperature?

a measure of the hotness or coldness of an object.

Although there is no temperature change during a change of phase, there is what?

a transfer of heat energy

When we have removed all the heat possible from an object (when the molecules are moving as slowly as possible), we have reached what?

absolute zero, the lowest possible temperature

A melting solid ________________ heat and a solidifying liquid _______________ heat.

absorbs/gives off

Who was Anders Celsius?

astronomer, was born in Sweden. He devised the centigrade scale of temperature in 1742. The Celsius scale (formerly the Centigrade scale) is named after him.

Since heat is a form of energy, we could measure it in joules or ft lb. However, it is measured in different units why?

because it was not known that heat was a form of energy when the other units were devised.

Why is water very useful in cooling systems in engines and power plants?

because water has a great ability to absorb heat energy

Who was William Rankine?

engineer and scientist, was born in Scotland. He is noted for his work on the steam engine, machinery, shipbuilding, applied mechanics, the new science of thermodynamics, and the theories of elasticity and of waves.

Anything below absolute zero temp cannot be reached because all ____________ is removed, but there is no limit to what?

heat/the highest temperature because we can always add more heat to a substance to increase its temperature.

The R value is ____________________ proportional to the thermal conductivity and ____________________ proportional to the thickness.

inversely/directly

An increase in the pressure on a liquid does what to its boiling point? How do automobile manufacturers take advantage of this?

it raises it/they pressurize the cooling systems in the automobiles to raise the boiling point of the coolant being used.

Who was Lord Kelvin (Sir William Thompson)?

mathematician and physicist, was born in Belfast, Ireland. He helped develop the law of conservation of energy and the absolute temperature scale (now named the Kelvin scale), did fundamental research in thermodynamics, presented the dynamic theory of heat, developed theorems for the mathematical analysis of electricity and magnetism, and designed several kinds of electrometers.

There is no _____________ equivalent of R-value

metric

To heat raise the temperature of a material, what must we do?

speed up its atoms; that is we must add energy to them.

Melting and solidification of substances occur at the same _________________.

temperature

Describe what atoms are like in materials at higher temperatures.

the atoms vibrate more rapidly than at low temperatures. Their velocity is higher at high temperatures, and thus their kinetic energy is greater.

When two substances at different temperatures are mixed together , heat flows from the ____________ body to the ______________body until they reach the same _____________. Part of the heat lost by the warmer body is transferred to the cooler body and part is lost to what? What is the act of warmer body heat being transferred to cooler body heat until they are both equal called?

warmer/cooler/temperature/the surrounding objects or the air/thermal equilibrium or method of mixtures

The equations describing the flow of heat through an object are very similar to what?

those for the flow of electricity.

The transfer of heat from one object to another is always from the ______________ object to the ______________ object.

warmer/colder

Most solids have a _______________ structure and a definite _____________ pint at any given _________________.

crystalline/melting/pressure

The ___________ symbol is not used when writing a temperature on the Kelvin scale.

degree

Heat flow is similar to the flow of what?

electrical charge.

Heat flow calculations are important because of concern about what?

energy conservation

The increase in volume of an expanding solid results in a decrease in ________________.

weight density

Do liquids generally expand?

yes

The driving potential for heat flow is what?

the difference in temperature between the hot and cold sides of the object.

Convection currents are caused by what?

the expansion of liquids or gases as they are heated. This expansion makes the hot gas or liquid less dense than the surrounding fluid. The lighter fluid is then forced upward by the heavier, surrounding fluid, which then flows into replace it.

When a solid is heated, its expansion is due to what?

the increased length of the vibrations of its atoms and molecules. This results in the solid expanding in all directions.

What is the mechanical equivalent of heat?

the relationships between heat and useful work that James Prescott Joule determined by experiments.

What happens at the point of saturation during condensation?

the vapor of the gas cannot hold any more moisture becomes separated from the vapor.

What is useful application of an expanding liquid?

thermometer

What is change of phase?

Sometimes called change of state, it is the a change in a substance from one form of matter to another.

Almost all forms of technology have concerns about ________________ and ___________________ transfer. Why?

temperature/heat/ because being able to measure heat transfer can mean the difference between the success and failure of many things, from steam heat to space travel.

What is thermal conductivity?

the ability of a material to transfer heat by conduction