Physics IGCSE Class May/June 2021
“Thermal Physics”
Ahmed Shawky El-Gendy
Cellular: +201011557162
0
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
1. Any substance is built up of tiny particles (diameter 10−9m), called
molecules, which are built of atoms.
2. The molecules of the same substance have the same properties and
differ than those of other substances.
Ahmed Shawky El-Gendy
Cellular: +201011557162
3. Molecules of any substance are in continuous state of random motion.
4. Molecules of any substance are separated by spaces called
intermolecular spaces.
5. Molecules of any substance act on each other with a force of attraction
"intermolecular force", which increases as the molecules become
closer.
6. The molecules have kinetic energy "K.E.", because they are moving,
and potential energy "P.E." because their motion keeps them
separated despite the attraction which is trying to pull them together.
*One of the most important conclusions based on the kinetic model, is
the description of the three states of matter.
Matter commonly exists in solid, liquid, or gaseous states.
The substances have definite volume
and definite shape.
The intermolecular spaces are small.
Strong intermolecular forces of
attraction or repulsion hold the
molecules together, so they can't
move freely, but it can only vibrate
about an equilibrium point in its
position.
1
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
A liquid has definite volume
but not a definite shape.
The intermolecular distances
are greater than in solids
Ahmed Shawky El-Gendy
Cellular: +201011557162
The intermolecular forces of
attraction are smaller than in
solids
The molecules vibrate and have
enough energy to exchange
positions with other molecules.
The gas has indefinite shape and
indefinite volume, a gas fills
completely the volume of the
container
The intermolecular distances
are very great.
The intermolecular forces of
attraction are negligible.
The molecules move about at
random, they collide with each
other and the walls of the container.
2
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
In 1827, Robert Brown was using a microscope to study
tiny grains of pollen suspended in water.
Ahmed Shawky El-Gendy
He noticed the pollen grains were constantly moving it
Cellular: +201011557162
was suggested that the motion was caused by vibrating
water molecules bumping into the pollen grains.
Brownian motion can be also seen when you look to
smoke trapped in a small glass container or "cell",
which has bright light shining through it from the side.
Smoke particles reflected the light falling on them and
they are seen as bright specks against a dark
background moving in random directions.
The relatively large and slow smoke particles surrounded by much
smaller and much faster air molecules; Air molecules bombarded the
smoke particles randomly from all directions causing smoke particles
to move randomly in Brownian motion.
░ N.B.
If the temperature increases, the bright specks would move faster due
to faster motion hitting them (and vice versa).
3
Ahmed Shawky El-Gendy
Cellular#: +201011557162
“Thermal Physics”
Ahmed Shawky El-Gendy
Cellular: +201011557162
0
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
1. Any substance is built up of tiny particles (diameter 10−9m), called
molecules, which are built of atoms.
2. The molecules of the same substance have the same properties and
differ than those of other substances.
Ahmed Shawky El-Gendy
Cellular: +201011557162
3. Molecules of any substance are in continuous state of random motion.
4. Molecules of any substance are separated by spaces called
intermolecular spaces.
5. Molecules of any substance act on each other with a force of attraction
"intermolecular force", which increases as the molecules become
closer.
6. The molecules have kinetic energy "K.E.", because they are moving,
and potential energy "P.E." because their motion keeps them
separated despite the attraction which is trying to pull them together.
*One of the most important conclusions based on the kinetic model, is
the description of the three states of matter.
Matter commonly exists in solid, liquid, or gaseous states.
The substances have definite volume
and definite shape.
The intermolecular spaces are small.
Strong intermolecular forces of
attraction or repulsion hold the
molecules together, so they can't
move freely, but it can only vibrate
about an equilibrium point in its
position.
1
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
A liquid has definite volume
but not a definite shape.
The intermolecular distances
are greater than in solids
Ahmed Shawky El-Gendy
Cellular: +201011557162
The intermolecular forces of
attraction are smaller than in
solids
The molecules vibrate and have
enough energy to exchange
positions with other molecules.
The gas has indefinite shape and
indefinite volume, a gas fills
completely the volume of the
container
The intermolecular distances
are very great.
The intermolecular forces of
attraction are negligible.
The molecules move about at
random, they collide with each
other and the walls of the container.
2
Ahmed Shawky El-Gendy
Cellular#: +201011557162
, Physics IGCSE Class May/June 2021
“Thermal Physics”
In 1827, Robert Brown was using a microscope to study
tiny grains of pollen suspended in water.
Ahmed Shawky El-Gendy
He noticed the pollen grains were constantly moving it
Cellular: +201011557162
was suggested that the motion was caused by vibrating
water molecules bumping into the pollen grains.
Brownian motion can be also seen when you look to
smoke trapped in a small glass container or "cell",
which has bright light shining through it from the side.
Smoke particles reflected the light falling on them and
they are seen as bright specks against a dark
background moving in random directions.
The relatively large and slow smoke particles surrounded by much
smaller and much faster air molecules; Air molecules bombarded the
smoke particles randomly from all directions causing smoke particles
to move randomly in Brownian motion.
░ N.B.
If the temperature increases, the bright specks would move faster due
to faster motion hitting them (and vice versa).
3
Ahmed Shawky El-Gendy
Cellular#: +201011557162
