Thermal Energy That’s so hot.
All matter is made of tiny little particles (atoms and molecules) All matter is made of tiny little particles (atoms and molecules) Those particles are never still Those particles are never still
They always move, even if it is just vibrating in place Moving objects have KE!!
Temperature is the average KE of all the particles of an object. Temperature is the average KE of all the particles of an object. Measured in kelvins (K) Measured in kelvins (K)
Knowing this, what does it mean to increase your temperature? Knowing this, what does it mean to increase your temperature? It means that your particles have more KE, which means they are moving faster! It means that your particles have more KE, which means they are moving faster!
Time for the people-are- molecules demo Time for the people-are- molecules demo
Thermal Energy (TE) is… The sum of the kinetic and potential energy of all the particles in an object. The sum of the kinetic and potential energy of all the particles in an object.
When Temperature increases, so does TE, because temp. is the KE of the particles, and KE of the particles is part of TE!
More mass also means more TE…why? Because if you have more mass, you have more particles. More particles means more KE and PE to add together!
Heat is TE that flows from higher temperature to lower temperature. Heat is TE that flows from higher temperature to lower temperature. Since it is a form of energy, it can be measured in joules Since it is a form of energy, it can be measured in joules
Objects do NOT transfer cold to each other, only heat! Objects do NOT transfer cold to each other, only heat! Heat wants to move only from warmer objects to colder ones Heat wants to move only from warmer objects to colder ones Once temperatures are equal, no more heat is transferred Once temperatures are equal, no more heat is transferred
Specific heat is the amount of heat it takes to raise the temperature of 1 kg of a substance by 1 K (same as raising it 1°C)
Basic knowledge everyone remembers from high school science class: Basic knowledge everyone remembers from high school science class: Metals have low specific heats Metals have low specific heats Water has a very high specific heat Water has a very high specific heat
What does it all mean?!?!?!?! What does it all mean?!?!?!?! Look at page 161, Table 1 Look at page 161, Table 1 Pretend you have 1 kg of water and 1 kg of iron Pretend you have 1 kg of water and 1 kg of iron Put 4,500 J of TE into both, which one will get hotter? Put 4,500 J of TE into both, which one will get hotter?
Coolants are used to cool things down. Coolants are used to cool things down. Would you want your coolant to have high or low specific heat? Would you want your coolant to have high or low specific heat?
If heat is the transfer of TE, then how does heat happen? If heat is the transfer of TE, then how does heat happen? Three ways! Three ways! Conduction Conduction Convection Convection Radiation Radiation
Conduction is the transfer of TE by collisions between particles of matter. Conduction is the transfer of TE by collisions between particles of matter.
Let’s all play human conductor!! Let’s all play human conductor!!
First, our volunteers start off as a solid (link elbows) First, our volunteers start off as a solid (link elbows)
Next, a liquid (unlink elbows, but stay close) Next, a liquid (unlink elbows, but stay close)
Finally, a gas (spread out) Finally, a gas (spread out)
ALL matter can conduct! ALL matter can conduct! But solids are better at it. But solids are better at it.
Metals are the best conductors because: Metals are the best conductors because: They have loose electrons that can move freely within the metal and transfer TE much faster. They have loose electrons that can move freely within the metal and transfer TE much faster.
Convection is the transfer of TE in a fluid by mass movements of matter. Convection is the transfer of TE in a fluid by mass movements of matter. Fluid: that which can flow (liquid and gas) Fluid: that which can flow (liquid and gas)
Heated fluids rise above the cooler fluids surrounding them. Heated fluids rise above the cooler fluids surrounding them.
The cooler fluid flows into the space the hot fluid was occupying The cooler fluid flows into the space the hot fluid was occupying
The cooler fluid heats, then rises, and the cycle continues The cooler fluid heats, then rises, and the cycle continues
Radiation is the transfer of energy by electromagnetic waves. Radiation is the transfer of energy by electromagnetic waves. Conduction and convection need matter to work; radiation does not! Conduction and convection need matter to work; radiation does not!
Radiant energy passes through most gases easily Radiant energy passes through most gases easily Radiant energy can pass through or be absorbed by most liquids Radiant energy can pass through or be absorbed by most liquids
Most solids will absorb radiant energy Most solids will absorb radiant energy Yes, there are always exceptions to every rule...that is why I said ‘most’ Yes, there are always exceptions to every rule...that is why I said ‘most’
As said before, all matter conducts! Some matter is really lousy at it Those types of matter are called insulators.
Insulators are substances that slow the transfer of TE from one place to another. Insulators are substances that slow the transfer of TE from one place to another.
One of the best insulators is air One of the best insulators is air Any material that has lots of air in it makes a good insulator Any material that has lots of air in it makes a good insulator
Fiberglass traps air pockets
Cotton insulation no itch!
Special information: how a thermos works Special information: how a thermos works They can keep warm stuff warm and cold stuff cold, but how? They can keep warm stuff warm and cold stuff cold, but how?
Combination of a vacuum and reflective surfaces
Vacuum : An absence of all matter, even air!! If there is no matter, then there is no conduction or convection
Reflective surfaces On both the inner and outer wall of the vacuum space On both the inner and outer wall of the vacuum space Reflects most radiant energy Reflects most radiant energy
THINK!!!! If a substance gets hotter, its molecules move faster Molecules moving faster will spread out
When molecules spread out, they take up more space When molecules spread out, they take up more space This makes the entire object take up more space This makes the entire object take up more space This is thermal expansion This is thermal expansion Also, the object becomes less dense Also, the object becomes less dense
Phase changes due to TE changes Gaining TE can make a substance go from solid to liquid to gas Gaining TE can make a substance go from solid to liquid to gas Losing TE can make a substance go from gas to liquid to solid Losing TE can make a substance go from gas to liquid to solid
Label the above graph of temperature change vs. time with the following: Label the above graph of temperature change vs. time with the following: - where is the substance a solid? - where is the substance a solid? - where is it a liquid? - where is it a liquid? - where is it a gas? - where is it a gas?
Heat is being added at a constant rate throughout the graph. There are two places where the temperature does not change for a certain length of time. What is happening during these times?
Phase Changes!!! During a phase change, the TE being added does NOT add to the temperature (average KE). The added TE is used to break the bonds between particles, increasing their PE This would mean melting for solids, evaporating for liquids
It works backwards too!!!! It works backwards too!!!! During phase changes from gas to liquid and liquid to solid, TE is lost During phase changes from gas to liquid and liquid to solid, TE is lost On the flat parts, this loss of TE is not causing a loss of KE On the flat parts, this loss of TE is not causing a loss of KE The TE is lost because the particles are bonding to each other, decreasing PE The TE is lost because the particles are bonding to each other, decreasing PE