Lecture 5: Thermal Energy and Heat
Rub your hands together quickly and they will become warm.
Apply breaks on a speeding car and they will heat up. These
examples suggest that energy of motion (kinetic energy) can be
converted into heat (thermal energy).
Lesson 7.1 Atomic Theory
Democritus’ contribution to this theory would be his idea that
all matter is made up of small particles called atoms. However, this
theory would not receive recognition until John Dalton proposed
Dalton’s atomic theory that can be summarized by the following
points:
1. Elements are composed of indivisible atoms. Elements are
pure substances that cannot be broken down through
chemical processes.
2. The atoms in an element have similar properties. However,
these atoms differ from other elements.
3. By combining different kinds of atoms, compounds can be
formed. A molecule is a group of two or more atoms linked
together.
4. Chemical reactions can be described as the rearrangement of
atoms.
Lesson 7.2 Kinetic Theory of Matter
Scottish botanist Robert Brown noticed that pollen grains
moved at a random manner, When he studied nonliving dye particles
under the same conditions, he noticed that same erratic motion in
individual particles of the dye, This is the Brownian Motion describes
as the erratic and random movements of small particles suspended in
a liquid or gas.
This would be further explained through the Kinetic Molecular
Theory which explained the behavior of a single gas atom.
1. Gas particles are assumed to be spherically-shaped objects
moving at a constant random rate.
2. The particles are assumed to move at a straight path until they
collide with each other or with the container.
3. The distances between each particle is assumed to be larger
than the size of the particle.
4. Attractive force between each particle is negligible.
5. These particles experience perfectly elastic collisions. No
energy is lost when they collide.
6. The kinetic energy of these particles is dependent on the temp
Lesson 7.3 States of Matter
Solids have fixed shape and definite volume. These are rigid, their
physical form does not bend or change unless exerted some force.
The attractive forces between atoms are strong enough to cause them
to vibrate in a fixed position.
Liquid takes the shape of its container but has a fixed volume. The
atoms and molecules move more quickly, the attractive forces
between them are weaker.
Gas has neither a fixed shape nor a definite volume; it will expand
indefinitely to fill the volume and shape of its container. The atoms
move very quickly and do not stay together causing them to move out
in all directions.
Lesson 7.4 Temperature
- Temperature is the measure of how hot or cold something is. In
physics, this is defined to be as the measure of the average kinetic
energy of the atoms and molecules in a substance. Thermometer -
used to measure temperature.
- Daniel Fahrenheit (1724) developed the first mercury thermometer
that is based on the property that materials expand when heated and
contract when cooled. He also developed the Fahrenheit scale.
- Ander Celcius introduced the Celsius/Centigrade scale and
became the standard for measuring temperatures. The freezing and
boiling points were set to 0°C to 100°C.
- Fahrenheit to Celsius
(Equation 7.1)
