65 terms

Chapter 6 Physical Science

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T or F: are particles in an object in a constant random motion in different directions?
T
When the object is hot, do the particles move faster or slower?
Faster
Does an object have more kinetic energy of they move faster?
Yes
Temperature
A measure of the average kinetic energy of the particles in the object.
In SI units, what is temperature measured in?
Kelvins
One kelvin degree = how many degrees Celsius?
One degree Celsius
Thermal energy
The sum of the kinetic and potential energy of all the particles in the object.
How does temperature relate to thermal energy?
The thermal energy increases because when the temp. goes up,the average kinetic energy (movement ) of the particles goes up, and since thermal energy (temperature) is the total kinetic (movement) and potential energy of all the particles in an object, the thermal energy (temperature) increases when the average kinetic energy (movement) of its particles increases.
Heat
Thermal energy that flows from something at a higher temperature go something at a lower temperature.
What is heat measured in?
Joules (energy is measured in joules too)
What is the specific heat of water?
4,184 (J/kg X degrees Celsius)
Specific heat
Amount of heat that is needed go raise the temperature of 1 KG of some material by 1 degree Celsius
How is specific heat measured?
Joules per (divided by) kilogram degree Celsius)
Coolant
A substance that is used to absorb heat
Why is the specific heat of water so high?
Water Molecules form strong bonds with each other
How does the thermal energy of an object change?
When heat flows into or out of the object.
How do you calculate change in thermal energy?
Change in thermal energy (J) = mass (kg) X change in temp. (Celsius or kelvins, use what your given) X specific heat (J/ kgC


Q= m(Tf-Ti) C
How do you measure the specific heat of a material?
A calorimeter
How does a calorimeter work?
The mass of a sample of the material is measured, as is the initial temperature of the water in the calorimeter. The material is then heated, it's temperature measured, and the sample is placed in the water in the inner chamber of the calorimeter. The sample cools as heat is transferred to the water, and the temperature of the water increases. The transfer of heat continues until the sample and the water are at the same temperature. Then the initial and final temperatures of the water are known, and the amount of heat gained by the water can be calculated.
How is thermal energy transferred from place to place?
Conduction, convection, and radiation.
Conduction
Transfer of thermal energy by collisions between particles in matter. (Particles are touching directly; particles with more and less potential energy collide)
Which state of matter does heat move faster in by conduction?
Solids and liquids
What are the best conductors of heat?
Metals
Why is a metal a good conductor?
Electrons aren't bound to individual atoms, and move easily through the metal. Collisions between the electrons and other particles let thermal energy to be transferred more quickly than other materials.
Convection
Transfer of thermal energy in a fluid by the movement of warmer and cooler fluid from place to place
What happens when convection occurs?
More energetic particles move from one place to another
What happens when particles move faster?
They tend to be farther apart, so a fluid expands as its temperature increases. It's volume increases, but mass doesn't. Density increases (density = mass/volume)
Where do less dense materials to?
To the top. As it rises it loses heat due to conduction to the cooler air around it. When warm air reaches the top, it's become cool enough that is now denser than the air at the bottom suburb sinks again. THIS IS CALLED A CONVECTION CURRENT)
What does a convection current do?
Transfers heat from warmer to cooler parts of the fluid. Conduction and convection transfer thermal energy.
How does heat reach earth?
Radiation
Radiation is...
The transfer of energy by electromagnetic waves
What happens when radiation strikes a material?
Some is absorbed, some is reflected, and some may be transmitted through the material.
what is the transfer of energy by radiation most important in?
Gases
Why is transfer of energy by radiation in gases easier?
The molecules are farther apart.
Insulator (wood, plastic, fiberglass, air)
Material in which heat flows slowly.
Why is a gas, such as air, a good insulator?
It contains many air pockets, which conduct heat poorly and keep convection currents from forming.
Forced air systems
Most common type of heating. Fuel is burned in a furnace and heats a volume of air. A fan then blows the warm air through a series of large pipes called ducts. The ducts lead to openings (vents) in each room. Cool air returns through other vents to the furnace to be reheated.
Radiator systems
Closed metal containers that contains hot water or stems. The thermal energy contained in the hot water or stems is transferred to the air surrounding the radiator by conduction. This warm air then moves through the room by convection. *** fuel burned in a central furnace beats a tank of water. A system of pipes carries the hot start to radiators in the rooms of the building. After the water cools, it flows through the pipes back to the water tank and is reheated. In some systems, water is heated to produce steam that flows through the pipes to the radiators. As steam coools, it condenses into water and flows back to the tank.
Electric heating systems
No central furnace. Electrically heated coils placed in floors and in walls heat the surrounding air by conductors. Heat is then distributed through the room by convection.
Passive solar heating
Materials inside a building absorbs radiant energy from the sun during the day, and heat up. At night when the building begins to cool off, thermal energy observed by these materials helps keep the room warm. Radiant energy from the sun is transferred to the room through windows
Active solar heating
Use solar collectors that absorbs radiant energy from the sun.
Thermodynamics
Thermal energy, heat, and work are related, and thermodynamics is study of the relationship among them
First law of thermodynamics
The increase in thermal energy of a system equals the work done on the system plus the heat transferred to the system. (AKA Energy cannot be created or destroyed. You cannot get more work out, than what you put in)
How do you know if a system is an open or closed system?
A system isOpen if heat flows across the boundary or if work is done across the boundary. Then energy is added to the system
Second law of thermodynamics
It is impossible for heat to flow from cold to warm unless work is done
How do you know if a system is closed?
No heat flows across the boundary and there is no outside work done
According to the first law of thermodynamics what happens to thermal energy of a closed system?
It doesn't change. There may be process is going on that are converting one form of energy into another, but the total energy of the system doesn't change. Total energy stays constant
What happens when heat flows from a warm object to a cooler object?
The thermal energy of the warm object decreases in the thermal energy of the cooler object increases
Can heat flow from a cold object to a warm object?
No because it violates the second law of thermodynamics. (example: if you hold an ice cube in your hands, no work is done. As a result he follows only from your warmer hand to the colder ice.)
Hear engine
A device that converts heat into work
What does a cars engine do?
It converts the chemical energy in gasoline into heat. The engine then transform some of the thermal energy into work by rotating the car's wheels. However only about 25% of the heat released by the burning gasoline is converted into work, and the rest is transferred to the engine surroundings
Internal combustion engine
The heat engine in a car in which fuel is burned inside the engine in chambers or cylinders
What does each cylinder container?
A piston that moves up and down. Each up-and-down movement is called a stroke. Cars and diesel engines have four different strokes. (1. Intake stroke 2.compression stroke 3. Power stroke 4. Exhaust stroke)
What happens in the intake stroke?
The intake valve opens as the piston moves downward, drawling a mixture of gasoline and air into the cylinder
What happens in the compression stroke?
Intake valve closes as the piston moves upward, compressing the fuel-air mixture.
What happens in the power stroke?
A spark plug ignites the fuel-air mixture. As the mixture burns, I guess his expand, pushing the piston down.
What happens in the exhaust stroke?
As the piston moves up, the exhaust valve opens, and the hot gases are pushed out of the cylinder
Why isn't all of the heat produced in internal combustion engine converted into useful work?
Friction between moving parts causes some of the work done by the engine to be converted into heat. However even if friction were totally illuminated, a heat engine still cannot be 100% efficient. Instead the efficiency of an internal combustion engine depends on the difference in the temperature of the burning gas inside the cylinder the temperature of the air outside the engine
How do you make the engine more efficient?
Increase the temperature of the burning gasses
How can the inside of the refrigerator stay cold?
The second law of thermodynamics prevent heat from flowing from inside the fridge to the warm room. However the second law allows heat to move from a cold to a warm object if work is done in the process. A fridge does work as it moves he from inside the fridge to the warm room. The energy to do the work comes from electrical energy The fridge obtained from an electrical outlet.you can think of a fridge as a heat mover that does work to move heat from a cooler temperature to a warmer temperature.
How does a refrigerator work?
It contains a coolant that is pumped through pipes on the inside and outside. The coolant is a special substance that evaporates at a low temperature. The colon is pumped through an expansion valve and changes into a gas. When it changes into a gas it cools. Cold gas is pumped through pipes inside the fridge, where it absorbs thermal energy. As a result the inside of the fridge cools. The gas is then palms to a compressor does work by compressing the guests. This makes the gas warmer and a temperature of the room. The one gas is pumped through the condenser coils. Because the gas is warmer than the room, normal energy flows from the gas to the rent. Some of this heat is a thermal energy that the coolant gas absorbed from the inside of the fridge. As the gas is off heat, it cools and changes to a liquid. The liquid coolant is then changed back to a gas, and the cycle is repeated.
How does an air conditioner work?
It's like a five refrigerator, except that warm air from the room is for stupid over to containing the coolant. The one air is cold in is forced back into the room. Thermal energy that is observed by the cooling is transferred to the air outdoors. Fridges and air-conditioners are heat in jeans working in reverse they use mechanical energy supplied by the compressor motor to move remove energy from cooler to warmer areas
How does a heat pump work?
It is a two-way heat. In warm weather, it operates as an air conditioner. In cold weather it operates like an air conditioner in reverse. The coolant gas is cooled and is pumped through pipes outside the house. there, the: absorbs heat from the outside air. The colon is then compress and back into the house, where it releases heat.
What is a human coolant?
Our sweat
How does the human coolant of sweat work?
Your body uses evaporation to keep its internal temperature constant. When a liquid changes to a gas, and G is of sword from the liquid surroundings. As you exercise your body generate sweat tiny glands with the new schedule. Is this what evaporates, carries away heat.