welcome back! agenda: 1. #throwbackthursday: question of the day #28 & 29 2. energy vocabulary...
TRANSCRIPT
WELCOME BACK!
Agenda:
1. #throwbackthursday: Question of the Day #28 & 29
2. Energy Vocabulary Quiz
3. Heat & Thermal Energy Notes
Homework: Energy Unit Quiz Review
Thursday, January 29, 2015Objective: Thermal Energy; I will discuss thermal energy and compare the different ways to transfer heat.
CRT Prep: Life Science #28 L.8.B.5 http://www.rpdp.net/sciencetips_v3/L8B5.htm
The explanation that diseases are caused by microorganisms is known as the
A. cell theory.
B. immune theory.
C. germ theory.
D. infection theory.
CRT Prep: Life Science #29 L.8.B.5 http://www.rpdp.net/sciencetips_v3/L8B5.htm
Exposure to a weakened or mild form of a pathogen to produce immunity is the basis for using a(n)
A. vitamin.
B. interferon.
C. vaccine.
D. antibiotic.
Thermal Energy
A. Temperature & Heat
1. Temperature is related to the average kinetic energy of the particles in a substance.
2. SI unit for temp. is the Kelvin
a. K = C + 273 (10C = 283K)
b. C = K – 273 (10K = -263C)
3. Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.
4. Thermal energy relationships
a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).
b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).
5. Heat
a. The flow of thermal energy from one object to another.
b. Heat always flows from warmer to cooler objects. Ice gets
warmer while hand gets
cooler
Cup gets cooler while hand gets
warmer
6. Specific Heat
a. Some things heat up or cool down faster than others.
Land heats up and cools down faster than water
b. Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K).
1) C water = 4184 J / kg C
2) C sand = 664 J / kg C
This is why land heats up quickly during the day and
cools quickly at night and why water takes longer.
Why does water have such a high specific heat?
Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds
and do not need as much energy to break them.
water metal
How to calculate changes in thermal energy
Q = m x T x Cp
Q = change in thermal energy
m = mass of substance
T = change in temperature (Tf – Ti)
Cp = specific heat of substance
c. A calorimeter is used to help measure the specific heat of a substance.
First, mass and temperature of
water are measured
Then heated sample is put
inside and heat flows into
water
T is measured for water to help get its heat gain
This gives the heat lost by
the substance
Knowing its Q value, its mass, and its T, its Cp can be calculated
QuestionQ: If a cup of hot chocolate and an ice cube were left on the table in this room what would happen to their Temperature? Why?
A: The cup of hot chocolate will cool until it reaches “room temperature.”
A: The ice cube will melt and then the liquid will warm to “room temperature.”
(Room temperature is about 25 Degrees C)
Heat Transfer• Heat always moves from a warmer place to a cooler
place. • So:
• Hot objects in a cooler room will cool to room temperature.
Heat EnergyHeated liquid/air
Cooler air
The air outside the mug is coolerthan the air inside the mug. So the heated air
moves out of the mug into the cooler air
The cooler air warms up and the mug cools down until both are about equal temperature
Heat Transfer• Heat always moves from a warmer place to a cooler
place. So:• Cold objects in a warmer room will heat up to room
temperature.
Heat Energy
All solids (ice) melt when they gain enough heat energy
Heat Transfer Methods• Heat moves from one place to another by:
•Conduction: Movement through direct contact.
•Convection: Circular motion of heated fluid material.
•Radiation: Light waves through a space or gas.
CONDUCTION:
When you heat a metal strip at one end, the heat travels to the other end.
As you heat the metal, the atoms vibrate faster, these vibrations make the adjacent atoms vibrate, and so on and so on, the vibrations are passed along the metal
and so is the heat.
Metal Bar
So it’s no wonder that you can hold metalover a flame without it burning your hand for
a few seconds, but after that…OUCH!!!
Watch as the atoms closest to theflame gain more energy first and
the energy simply spreads out
Heat Energy
It takes a little time, but the Heat Energy spreads out and the
metal gets “hotter”
Why Metals heat up so fast?
In addition to atom vibrations, the electrons for metal atoms can “drift”; are free to move around
within the metal.
When the metal is heated, the electrons gain kinetic energy and transfer it throughout the metal.
“Insulators”, such as wood and plastic, do not have drifting electrons which is why they do not conduct heat as well as metals.
= electron
HeatEnergy
Why does metal feel colder than wood, if they are both at the same temperature?
Metal is a conductor, wood is an insulator. The metal conducts the heat away from your hands, the wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.
The hand holding the metal is losing heatto the metal so it feels cooler!
CONVECTION:
Warmer, less dense liquids and gases (fluids) spread out and rise
up.
Cooler, more dense liquids
and gases (fluids) sink (move down).
= “cool” atom
= “hot” atom
Convection: Movement of Heat in a “circular” motion
Hot water rises
Cooler water sinks
That’s why its called a “Convection Current!”
Cools at the surface
Heat source
Warms back up again.
Hot water rises back
up
Demo: Oil & Thyme
How does this work in a liquid?
A “current” is a “steady flow” of a “fluid” (liquid and gas)
Cold air sinks
Where is the freezer
compartment put in a fridge?
Freezer compartme
nt
It is put at the top, because cool air
sinks, so it cools the
food on the way down.
It is warmer at
the bottom, so
this warmer air rises
and a “convection current”
begins.
Why is it windy at the seaside?
When the cool air reaches the surface of the water, there is nowhere else for it to go
So it moves sideways towards the shore and we feel this motion as a breeze
As the cool breeze reaches the land, it heats up, and rises as well!
And we get convection currents of air!
The third method of heat transfer:
There are no atomic particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ?
RADIATION=The transfer of heat by electro-magnetic waves!
Also Known as “Light!”
How does heat energy get from the Sun to the Earth?
Radiation helps keep our planet warm
Notice that some of the heat gets “trapped” bythe atmosphere and stays here = planet stays warm!
But some of it escapes back out intoSpace = planet doesn’t warm up too much!
There is a lot of energy in Solar Radiation:
Sunburns are because of Radiation impacting our skin
After the atomic bomb in Japan. There was once a large city where this photo is looking.
Now it is completely destroyed!!! (it only took about 1 second!!!)
Much of this destruction was caused byradiation
There was so much Radiation energy when the bomb blew up that some people
were simply vaporized!!! YIKES!!!