106 terms

# 7th grade science CH 7-temperature and thermal energy

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kinetic energy
energy a moving object has that increases as the speed of the object increases
temperature
measure of the average kinetic energy of the individual particles of a substance
do molecules move faster in hot or cold water
molecules move faster in hot water because the higher the temperature the faster the molecules move
thermal expansion
almost all substances expand and contract when they are heated and cooled- the amount of expansion and contraction depends on the type of material and the change in temperature
why do materials expand when their temperatures increase?
when the temperature of an object is increased, its molecules speed up and tend to move farther apart
thermometers
use the expansion and contraction of materials to measure temperature
what is the most practical instrument to measure temperature
thermometer
what are two common temperature scales
fahrenheit and celsius
what is freezing and boiling on the fahrenheit scale
32 degrees and 212 degrees fahrenheit- the space between the boiling point and freezing is 180 degrees
what is freezing and boiling on the celsius scale
0 degrees and 100 degrees
why are celsius degrees bigger than fahrenheit degrees
because there are only 100 degrees between the boiling and freezing point of water
fahrenheit to celsius formula
C=(5/9)*(F-32)
celsius to fahrenheit formula
F= 9/5 x C +32
kelvin scale
freezing = 0; boiling= 273
potential energy
stored energy- energy that the molecules have that can be converted into kinetic energy
thermal energy
the sum of the kinetic and potential energy of the particles in a material- the total energy of the particles in a material
explain the difference between temperature and thermal energy. How are they related?
Temperature of an object depends on the average kinetic energy of the molecules in an object / Thermal energy depends on the sum of the kinetic and potential energy of the molecules in an object
Determine which temperature is always larger- an object's Celsius temperature or it's Kelvin temperature.
Kelvin temperature will always be greater than Celcius because you have to add 273 degrees to the Celcius temperature to get the Kelvin temperature
Explain how kinetic energy and thermal energy are related.
In order to find the thermal energy you add up the kinetic and potential energies of the molecules in an object
describe how thermometer uses the thermal expansion of a material to measure temperature.
As temperature gets hotter, the liquid in the thermometer expands and rises
Heat
movement of thermal energy from a substance at a higher temperature to a substance at a lower temperature
How is it decided on how much heat is transfered between 2 objects?
it depends on the difference in temperature
how is heat transferred?
it always moves from warmer to cooler objects.- never from cooler to warmer. the warmer object loses thermal energy and becomes cooler and the cooler object gains thermal energy and becomes warmer.
How does the transfer of heat occur?
conduction
transfer of thermal energy by direct contact; Occurs when energy is transferred by collisions between particles--- the transfer of heat by direct contact.
where does conduction usually occur?
it usually occurs most easily in solids and liquids, where atoms and molecules are close together.- the atoms and molecules are closer together and only need to go a short distance before they bump into each heat is transferred energy more quickly -- faster than with gases
why does conduction occur more easily in solids an liquids than in gases?
the atoms and molecules are closer together and only need to go a short distance before they bump into each heat is transferred energy more quickly -- faster than with gases
the transfer of energy by electromagnetic waves
how is heat transferred between the sun and the earth?
How does heat transfer by radiation occur?
when energy is transferred by electromagnetic waves. they carry energy through empty space, as well as through matter, solids, liquids, and gases.
all objects emit electromagnetic radiation; ex- the warmth that the fireplace puts off as you sit by it
Explain how the thermal energy of ice cubes changes?
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conduction
transfer of thermal energy by direct contact; occurs when every is transferred
convection
transfer of thermal energy by the movement of particles from place to another in a gas or liquid
transfer of heat by convection
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thermal insulators
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forced convection
outside force pushes a fluid such as air or water to make it move and transfer heat
conductor
materials in which electrons can move or that transfers heat easily
what are the best conductors of heat
gold and copper because the electrons move are loosely held and can bump into other atoms easier
on a hot day, why is pavement hotter than the grass?
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specific heat
amount of heat needed to raise the temperature of 1 kg of a substance by 1 degree celsius
thermal pollution
increase in temperature of a natural body of water; caused by adding warmer water
how does thermal pollution affect sea life?
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How do you reduce thermal pollution?
thermal pollution can be reduced by cooling the warm water produced by factories, power plants, and runoff before it is released into a body of water. Cooling towers are used to do this.
Heat Engine
device that converts thermal energy into mechanical energy
chemical energy
is energy stored in the chemical between atoms
the energy stored in the chemical bonds between electromagnetic waves
Nuclear energy
the energy stored in the nuclei of atoms
Electrical energy
the energy carried any electric charges as they one in a circuit
Does the total amount of energy ever change
No- when energy is transformed from one form to another the total amount of energy doesn't change- energy cannot be created or destroyed
How can energy be changed
it can only be transformed from one form to another
internal combustion engines
heat engine in which fuel is burned in a combustion chamber inside the engine; ex. planes, bus, lawn mowers, boats,etc.
How is the power of an engine decided
the more cylinders, the more power it produces
How does the burning of fuel mixture cause a piston to move?
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How can a refrigerator be cooler inside than the air in the kitchen?
A refrigerator is a heat mover. It absorbs thermal energy from the food inside the refrigerator
What material does a refrigerator contain?
coolant
What is a Coolant
it is a substance that carries thermal energy from the inside to the outside of the refrigerator
What also uses a coolant
air conditioners
What does a heat pump do?
it moves thermal energy from one place to another
What does a heat pump do with cooling?
it removes thermal energy to indoor air and transfers it outdoor air
Tell why diesel engines don't use spark plugs?
in a diesel engine, the air in a cylinder is compressed to such a high pressure that it is highly flammable fuel ignites without the help of a spark from a plug.
What is the source of thermal energy in an internal combustion engine?
...The thermal energy is converted into mechanical energy as a gasoline is being burned under pressure.
Tell whether you could cool a kitchen by keeping the refrigerator door open?
No you can't, because the coolant couldn't pump through the pipe and get rid of the thermal energy.
Tell how a refrigerator uses a coolant to keep the food cool?
the coolant carries the thermal energy from the inside of the refrigerator to the outside of the refrigerators.
Explain how an air conditioner could also be used to heat a room.
The thermal energy from the outside of the house is absorb by a coolant with in the pipes os the air conditioner. Then the warm coolant would travel through the pipes inside the house. Thats where the thermal energy would transfer to the air inside of the house.
What machine cools the same way a refrigerator does?
air conditioner
How are internal combustion engine and heat different and related?
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How are temperature and thermal energy different and the same?
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How are thermal energy and thermal pollution different and the same?
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How are conduction and convection different and the same?
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How are conduction and heat different and related
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How are heat and specific heat different and related?
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How are conduction and radiation different and related?
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How are convection different and related?
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How are a conductor and heat different and related?
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What source of thermal energy does an internal combustion engine use?
burning fuel
What happens to most materials when they become warmer?
they expand
Which occurs if two objects at different temperatures are in contact?
conduction
Which of the following describes the thermal energy of particles in a substance?
average value of all kinetic and potential energy.
Heat being transferred from the Sun to Earth is an example of which process?
Many insulating materials contain spaces filled with air because air is what type of material?
insulator
A recipe calls for a cake to be baked at a temperature of 350 degrees Fahrenheit. What is this temperature on the celsius scale?
177 degrees celsius
Which of these is the name for thermal energy that moves from a warmer object to a cooler one.
heat
Water is a poor conductor of heat. Yet when you heat a pan, the surface gets hot quickly, even though you are applying heat to the bottom of the water. Explain.
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Explain why several layers of clothing often keep you warmer than a single layer.
It is a good insulator and has more air pocket for better insulation.
Identify the phrase "heat rises" is sometimes used to describe heat . for what type of materials is this phrase correct. Explain.
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Explain why concrete sidewalks are usually made of slabs of concrete. Why do the concrete slabs have a space between them?
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Explain how a winter jacket is lined with insulating material that contains air spaces. How would the insulating properties of the jacket becomes wet? Explain.
If it started to rain or the air pockets got blocked off.
Compare two glasses of water are poured into a pitcher. If the temperature of the water in both glasses was the same before they were mixed, describe how the temperature and the thermal energy of the water in the pitcher compares to the water in the glasses.
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describe 3 ways heat is transferred
conduction; by direct contact
radiation; electromagnetic waves carry thermal energy convection; transfer of thermal energy by the movement of molecules (natural and forced)
explain how temperature is related to kinetic energy
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identify materials that are insulators or conductors
insulators are anything that air can flow through (fur, foam, feathers, sand)
conductors are solid and liquids (metal, copper, and gold)
the temperature of the two glasses of water shown in the photograph above are 30 degrees C. Which of the following is a correct statement about the two glasses of water?
the molecules of the warmer water have more kinetic energy
the difference in temperature of the tow glasses of water is 30 degrees C. What is their difference in temperature on the Kelvin scale?
30K
Which of the following describes a refrigerator?
heat mover
Which of the following is not a step in the four-stroke cycle of internal combustion engines?
idling
a sample of each of the metals in the table above formed into a 50-g cube. If 100 j of heat are applied to each of the samples, which metal would change temperature by the greatest amount?
aluminum
An internal combustion engine converts thermal energy to which of the following forms of energy?
mechanical
If you add ice to a glass of room-temperature ice, does the water warm the ice or does the ice cool the water? Explain
the water warms the ice because there is more thermal energy than ice and convection occurs where the neighboring particles collide with other neighboring particles.
Strong winds that occur during a thunderstorm are the result of temperature differences between neighboring air masses. Would you expect the warmer or the cooler air mass to rise above the other?
warmer air would rise because heat rises in the direction of warmer to cooler.
What are the two main events that occur while the cylinder moves downward during the intake stroke of
the piston moves downward while there is a air mist fuel injected into the intake valve.
Why are cooking pots like the one in the photograph above often made of metal? Why isn't the handle made of metal?
cooking pots are often made of metal because they are good conductors of heat. The handle isn't made of metal because metal is such a good conductor it gets hot really fast. An insulator like plastic is put on the handle because an insulator has air pockets that trap air to cool the object.
The illustration above shows the parts of a refrigerator and how coolant flows through the refrigerator. Explain how thermal energy is transferred to the coolant inside the refrigerator and then transferred from the coolant to the outside air.
Thermal energy is transferred by a coolant. The coolant absorbs the thermal energy from the food and transfers it through pipes back out to the outside of the refrigerator.
Define temperature and explain how it is related to the movement of molecules in a substance.
Temperature is the average value amount of kinetic energy of a particle in a substance. It is related to molecules because if molecules move faster it is kinetic energy, which is the average amount of temperature.
Explain what makes some materials good thermal conductors.
Thermal conductors are good because of the types of atoms or chemical compounds they are made up of
You place a cookie sheet in a hot oven. A few minutes later you hear a sound as the cookie sheet bends slightly. Explain what causes this.
Convection causes the cookie sheet to bend because when two neighboring particles collide it changes the thermal energy.