# 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

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

C=(5/9)*(F-32)

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.

### 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 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

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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

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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

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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

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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

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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

coolant

### What is a Coolant

it is a substance that carries thermal energy from the inside to the outside of the refrigerator

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.

air conditioner

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burning fuel

they expand

conduction

### Which of the following describes the thermal energy of particles in a substance?

average value of all kinetic and potential energy.

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

heat

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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.

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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.

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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)

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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

30K

heat mover

idling

aluminum

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.

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