Science—Heat and Temperature Summary/Study Notes
I think that you covered this material with Mr. Brunett.
1. Warmed air molecules spread out or expand.
2. Cooled air molecules move closer together or contract.
3. Not all materials expand or contract at the
same rate.
4. People started to need to know the
temperatures of things as technology developed.
The Italian scientist, Galileo, invented the first thermometer,
which
contained mostly air. It took about 150
years to perfect the mercury-in-glass thermometer that is common today. This date, 1750, coincided with the start of
the Industrial Revolution, when technological changes meant that it was
more
important to be able to measure temperatures accurately. (thermo
= heat; meter = measuring device)
5. Instruments for measuring temperature are
important because not everyone experiences heat or cold in the same
way, so
estimates are unreliable. People have
different tolerances for heat and for cold.
6. Changes in temperature can bring about
changes in substances, and thermometers make use of these changes. Examples of substances whose changes in
temperature have been calibrated (measured and marked off because they
have
been found to have consistent changes with temperature) include air,
alcohol
and mercury.
7. You can make an air thermometer, but a major
problem is that you would have to recalibrate it every time you used it. This is because of changes in air
pressure. On high pressure days, with
fine weather, the air in the thermometer will occupy less space. On low pressure days, with rainy weather, the
air in the thermometer will occupy more space.
This is why most commercial thermometers use liquids rather than
air—they are not affected by changes in air pressure.
8. In about 1700, scientists learned that pure
substances always melted and boiled at fixed temperatures, and that
they could
use these fixed points to calibrate their thermometers.
A scientist named Fahrenheit built a mercury
thermometer with a cylindrical bulb, and invented a calibration scale
where
water froze at 32°and water boiled at 212° in 1717. Celsius, another scientist, invented the
centigrade (or Celsius) scale and built a mercury-filled thermometer
that had
100 degrees between the freezing and boiling points of water.
9. Clinical thermometers, used to measure body
temperature, have a constriction (kink) in the fine tube, just above
the bulb
of mercury, so that the mercury thread breaks at the constriction and
the
patient’s temperature can still be read.
10. Weather station thermometers also use
thermometers with constrictions so that the highest temperatures can be
recorded before the mercury is shaken down again. They
also contain a dumbbell-shaped object
called an index that allows the minimum temperature to be recorded.
11. We can tell the temperature of stars by
looking at their colours through various filters attached to their
telescopes.
12. A furnace thermostat uses a bimetallic strip
(ie, two metals, like iron and brass) and a mercury switch to control
when the
furnace turns on or off. When the
bimetallic strip coils up, the glass capsule containing the mercury
tilts
downward. The mercury slides and touches
the two contacts, so that the furnace turns on.
Electric irons and ovens are also controlled by thermostats
containing
bimetallic strips. When the iron is hot,
the brass expands more than the iron, causing a break in the electrical
circuit. When the bimetallic strip cools
down and contracts, the gap closes and the electricity can flow again.
A
thermocouple is a
thermometer that uses two different metals that touch to produce tiny
amounts
of electricity to measure temperature.
The amount of electricity produced depends on the temperature. Thermocouples are used in places like
smokestacks where people cannot go to read a thermometer.
They can read higher and lower temperatures
than a liquid-based thermometer can. They
can be connected to computers to record temperatures.
Resistance
thermometers (platinum) also use electricity to measure very high or
low
temperatures.
An
optical pyrometer
can be used to measure temperature changes by analyzing changes in the
light
given off by very hot or cold objects (as in space).
Thermographs
measure
temperatures in the everyday range, using infrared light to measure
temperature. They can show very small
differences in temperature.
13. You can get heat from a match; heat from
dissolving; heat from friction; heat from electricity.
14. Mixing hot and cold: there is a formula.
15. Joule, a British scientist, was interested in
changing mechanical energy into heat. It
took him 35 years to figure out exactly how much heat could be made
from a
definite amount of mechanical energy. He
figured out that the same amount of heat always came from a given
amount of
mechanical energy, showing that heat is a form of energy.
The unit in which energy is measured is the
joule (J). It is the amount of energy
you use to raise a 100 g weight 1 m. IT
takes 4.2 J of heat to raise the temperature of 1 g of water by 1°
Celsius. A device called a calorimeter
measures the amount of heat.
16. Energy comes from food. Each
type of food gives off a certain amount
of energy. A bomb calorimeter is used to
determine the amount of energy given off by a particular food.
17. The unit known as the calorie is used to
record energy content in food. Multiply
calories by 4.2 to convert them to kilojoules.
Young teenagers need 8000 to 10 000 kJ per day.
You will put on about 1 kg of mass for every
35 000 kJ you consume in excess of what your body needs.
This is probably review, too.
Hand
check—when you
hold up your hands in cold outside air, both feel equally cold. When you place one hand in water first, it
will feel much colder. Why?
Evaporation requires energy. This
energy is taken from the wet hand in the
form of heat. As water takes heat from
the hand, the hand gets colder. Water
accepts energy much quicker than air, so the dry hand stays warm longer. This proves that heat is energy.
We rely
on the sense
of touch to tell how hot and how cold things are, but this is not a
very
reliable way to estimate. It can also be
dangerous.
Hypothesis: a set of ideas that a scientist puts together
to explain an event in the natural world.
If the
ideas cannot
be proven false, they become a theory.
Temperature
is the
measure of the energy level of an object.
Heat is
the energy
that transfers from a hotter object to a cooler one.
The
scientist
Lavoisier believed that heat was a liquid called caloric that
transferred from
one object to another. His idea was disproved by Thompson, who
discovered that
there was no change to the mass of water that was frozen into ice. Because there was no change in mass, there
could be no caloric. Heat had to be
energy.
Changes of state
Solid—definite mass and shape,
Liquid—takes the
shape of its container
and may be penetrated by a solid object
Gas—has no
definite shape and very little
mass.
The
volume of a
material or an object is the amount of space it occupies.
Air is
a mixture of
gases.
When a
substance is
heated, it spreads out and occupies more space; in other words, its
volume
increases. This increase in volume is
called expansion.
When a
substance is
cooled, the air occupies less space and its volume decreases. This is called contraction.
Although
all
substances expand when heated and contract when cooled, they do so by
different
amounts.
Practical
applications: heating a jar lid to make it easier to remove; choosing
the right
materials to fill teeth
When a
substance
changes from solid to liquid, it melts.
When it
changes from
a liquid to gas, it is called evaporation.
When a
gas changes to
a liquid or solid, it produces precipitation (eg rain or snow).
Sublimation—heating
a solid to become a gas, and then cooling it back to solid form in
order to
purify it.
Transpiration—the
action of giving off gas or water vapour (moisture) through the skin or
other
surface.
Exothermic
reaction—two or more chemicals that, when combined, create a bond
which
changes the state of matter of the combination.
Exothermic reactions cause a change in state; a temperature
increase
(fire); smoke; and becomes unstable.
Endothermic
reaction—an internal reaction which causes heat to be released
(eg—the
body)
Kinetic Molecular
Theory
-can be
understood in
terms of energy converters
-molecules
convert
heat energy to kinetic (motion) energy.
As heat energy is added to a group of molecules, kinetic energy
is
converted to heat energy as heat energy is removed from the system.
-temperature
is the
average kinetic energy of a substance
-I f
the temperature
of a substance is high, this means that the molecules have lots of
kinetic
energy that can be converted into heat energy.
Does
high temperature
always mean lots of heat? No, because
there might not be the same amount of molecules. Example:
a match and a firepit are the same temperature, but a match only
has a
small range of heat, while if you stand away from a firepit, you can
still feel
the heat.
Diffusion—Particle
Theory of Matter
-all
matter is made
up of atoms, and groups of atoms make molecules
-molecules
have a way
of spreading out
-molecules
spread out
into the atmosphere in order to find their comfort zone
-once
molecules have
found that optimal space, they stop spreading out
-the
pop can
experiment demonstrates this: as the can
heats up, the molecules inside spread out and bounce around and become
more
diffuse. Some of the molecules also
become vapour (gas). When the molecules
are more diffuse, they put pressure against the walls of the can. Once the can has touched the cold water, the
molecules inside become less diffuse and shrink together to relieve the
pressure from the can’s walls. The walls
are weakened from the heat and the higher pressure of the water outside. The can collapses the walls of the can onto
the less diffuse molecules of the can.
In any
substance, the
particles have average energy.
Temperature is the measure of this average energy.
The
particle theory
explains expansion and contraction (through particulate movement).
The
movement of
particles also explains changes of state.
Sources of Heat
I think that this is new material.
Heat is
created from
five main sources:
a) chemical energy—stored in foods and
fuels. The chemical process of burning
(digestion) releases the heat from the foods and fuels into the body. The heat is released gradually so that there
is no damage to your body.
b) electricity—can be used as a source of heat,
but it must be produced first, through systems like moving water
(hydroelectricity) or through generating stations that burn coal (which
causes
pollution). This energy can then be sent
through wires into homes and businesses.
c)
mechanical—the
measure of average energy of particles in a substance.
If the particles move more quickly, the
energy increases and the substance gets hotter.
This type of energy is created by friction.
d) geothermal—energy produced deep inside the
Earth, where it is very hot. Energy gets
out through geysers or volcanoes. Some
people use hotsprings and other sources of geothermal energy to heat
their
homes (
e) solar—the sun produces heat and solar
energy. Some homes are made to use solar
energy. They need large south-facing
windows and walls and floors made of concrete.
At night, the concrete releases the heat into the house.
Renewable and Non-Renewable Heat Sources
1) Renewable Energy: those
that are not destroyed or used up in
the process of being used.
Examples: hydroelectric;
geothermal;
solar
2. Non-Renewable Energy: those
that are being used up over time and
one day may be used up completely.
Examples: chemical, mechanical,
coal-produced
Everyone
in our
society will someday have to change our lifestyles in order to save our
environment. A day will come when there
will be no resources left if we continue to waste or disregard
nonrenewable
resources.
Plant
and animal
material in garbage can be burned to produce heat, and can also produce
fuels
such as methane and methanol. Nuclear
energy is also a source of heat. Solar
energy, light, microwaves, infrared light, ultraviolet light and x-rays
are all
examples of radiant energy.