عقرب
01-01-2003, 11:49
For People Who Love Physices Only:D
1
Matter exists in three states: solid,
liquid and gas. A solid, for example
a stone, has a definite shape and a
definite volume. A liquid, such as
oil, has a definite volume but no
definite shape.
Matter
2
A gas, e.g. hydrogen, has neither
definite shape nor definite volume.
Water can exist in all three states:
below 0 degrees celsius it is a
solid (ice). Between 0 and 100 degrees
celsius it is a liquid (water).
Matter
3
Above 100 degrees water becomes a gas
(vapour). All matter consists of
elements such as zinc or oxygen, or
of compounds such as nitric acid or
sulphur dioxide. The smallest particle
of an element is called an atom.
Matter
4
The smallest particle of a compound is
called a molecule. A molecule of
sulphur dioxide is a compound of one
atom of sulphur and two atoms of
oxygen. A molecule of water is two
atoms of hydrogen and one of oxygen.
Molecules
5
When we measure quantities of matter,
we may use the fundamental units of
time (e.g. the second), mass (e.g. the
kilogram) and length (e.g. the metre).
We may also use units such as area,
volume or density.
Measurements
6
The area of a rectangle is found by
multiplying the length by the width.
The volume of a cylinder is equal to
Pi times the radius squared times the
height. The density of a substance
equals the mass divided by the volume.
Measurements
7
We use the terms specific gravity or
relative density to indicate density
relative to water. Gold has a density
of 19.3 grams per cubic centimetre.
So one cubic cm of gold has 19.3 times
the mass of 1 cubic cm of water.
Specific Gravity
8
A liquid takes the shape of the
container in which it rests. It also
pushes sideways against the sides, and
downwards on the bottom of the
container, and upwards against anything
placed in it.
Liquids
9
The existence of the force which is
exerted upwards is called buoyancy.
The law on buoyancy states: An object
immersed in a liquid appears to lose an
amount of weight which is equal to the
weight of the liquid it displaces.
Buoyancy
10
A stone with a mass of 3.2 kg is
suspended from a spring balance and
lowered into some water. The spring
balance now reads 2.2 kg, indicating
that the stone has displaced 1 kg (or
one litre of water).
Buoyancy
11
The Earth's atmosphere, the air we
breathe, consists of a mixture of
gases. Air has mass and exerts
pressure. At sea level, this pressure
is sufficient to support a 76 cm column
of mercury in a vacuum tube.
Gases
12
Changes in the weather cause small
changes in the atmospheric pressure.
A barometer is the instrument used to
measure these changes. The aneroid
barometer consists of a vacuum cell
attached by levers to a pointer.
Gases
13
The greater the pressure that is
applied to a gas, the less space it
will occupy. Boyle's law states: If
the temperature of a fixed mass of gas
remains constant, the volume will be
inversely proportional to the pressure.
Gases
14
Charles' Law and the Pressure Law also
describe the relationship between the
temperature, pressure and volume of a
gas. If one of the 3 values is
constant, the other 2 values are found
to be in direct or inverse proportion.
Gases
15
If a quantity has magnitude (size or
amount) and direction, it is a vector
quantity. If it has magnitude but no
direction, it is a scalar quantity.
Force is a vector quantity. Gravity is
an example of a force.
Force
16
Newton's law of gravity states that:
The force of attraction which exists
between two bodies is directly
proportional to their masses, and
inversely proportional to the square
of the distance between them.
Gravity
17
The Earth's gravity pulls downwards on
every particle of a body with a force
equal to the weight of that particle.
The sum of these forces appears to act
through the centre of gravity of the
body.
Gravity
18
If a body is not at rest, it is in
motion. The rate at which the body is
moving is called its speed. Speed is
calculated by dividing the distance by
the time (v = s/t) and is therefore a
derived unit.
Motion
19
The term velocity is used to mean speed
in a given direction. It is therefore
a vector quantity. If we multiply the
mass of a body by its velocity, we
obtain its momentum. The formula for
this is M = mv.
Motion
20
The rate at which the velocity of a
body changes is called acceleration,
and acceleration is calculated by
dividing the change in velocity by
the time taken. Acceleration is often
expressed in metres per second squared.
Motion
21
Work is done when a force moves a load
over a certain distance. The capacity
to do work is called energy. Energy,
like work is measured in joules. It
is a scalar quantity, having magnitude
but no direction.
Work & Energy
22
Mechanical energy exists in two forms:
a) kinetic energy, the energy a body
possesses because of its motion, and
b) potential energy, the energy a body
possesses because of its position or
state.
Work & Energy
23
The rate at which work is done is
power. This is expressed by the
formula P = W/t, where W is the amount
of work done or energy expended, t is
the time taken and P is the power.
One joule per second is a watt.
Power
24
In a hydro-electric power station, the
potential energy of the water behind
the dam is converted into electrical
energy. The water falls with great
force through pipes. This provides the
kinetic energy to drive the turbines.
Power
25
In general, when heat is applied to a
substance, its temperature rises. The
change in temperature can be measured
by a thermometer. When heated, most
substances expand, and they contract
when cooled.
Heat
26
Different substances have different
coefficients of expansion, i.e. they
expand by different amounts when
exposed to the same change in
temperature. E.g. lead has a higher
coefficient of expansion than concrete.
Heat
27
Heat may be transmitted in three ways.
The first is by conduction through a
material, which takes place, for
example, when one end of a copper tube
is heated and the heat is conducted to
to the other end.
Heat
28
Heat is also transmitted by convection
through the movements of a liquid or
gas, such as when warm air passes from
one part of a building to a higher part
of the building. Another way is by
radiation of heat waves.
Heat
29
Poor conductors of heat are good
insulators, and a vacuum is the best
insulator. The common thermos or
vacuum flask, in which we may keep food
hot or cold, is designed according to
this principle.
Heat
30
Some materials can absorb and give off
much more heat than others. For
example, if a piece of iron and a piece
of lead of equal size are heated to the
same temperature and left to cool, the
lead will cool much more quickly.
Heat
31
The specific heat of a substance is the
heat required to raise the temperature
of unit mass of that substance
through one degree celsius. Heat
used to be measured in calories, but
the modern unit is the joule.
Heat
32
Heating a substance does not always
raise its temperature. If we heat
crushed ice, the ice changes to water
but the temperature remains the same.
Also the temperature of boiling water
does not rise when heated further.
Heat
33
All pure substances change their states
at fixed temperatures, the melting
point and the boiling point. The heat
which changes the state without
changing the temperature is called
latent heat.
Heat
34
Sound waves are waves of compression.
This means that they require a medium
through which to travel. As the waves
pass through the medium, the particles
of the medium vibrate or oscillate.
Sound cannot travel through a vacuum.
Sound
35
Sound waves will travel through solids,
liquids and gases. Sound waves travel
at a speed of 340 metres per second
through air, through water at 1,450
metres per second and through iron at
5,125 metres per second.
Sound
36
As waves pass through a medium, the
maximum amount that a particle of the
medium moves is called the amplitude of
the wave. The amplitude depends on the
quantity of energy carried by the wave.
Wavelengths are measured in metres.
Wave Motion
37
The number of complete vibrations or
oscillations in each second is the
frequency of the wave. Wave frequency
is measured in hertz. It follows that
the wave speed is the product of the
wavelength and the wave frequency.
Wave Motion
38
Light radiation, like the radiation of
heat or radio waves, is an example of
electromagnetic radiation. Light
travels much faster than sound, at a
speed of around 300,000 km/s, and light
rays travel in straight lines.
Light
39
When light moves from one medium to
another, e.g. from air to water, the
rays change direction. We call this
refraction and say that the rays are
refracted. The refraction depends on
the refractive index of the medium.
Light
40
Lenses are used to control the
refraction of light. A converging
lens is one which causes the light
rays to come together and a diverging
lens is one which causes the light
rays to spread out.
Lenses
41
When parallel light rays strike a
diverging lens, they appear to come
from a point on the same side as the
source of the light. This point is the
virtual focus. A short-sighted person
needs glasses with diverging lenses.
Lenses
42
White light consists of a mixture of
colours. In a vacuum all these colours
travel at the same speed, but in matter
their speeds are slightly different.
Therefore we can use a prism to make
the colours disperse.
Colour
43
Any colour can be produced by using the
correct proportions of red, green and
blue light. These are therefore known
as the primary colours. Red and blue
produce magenta; red and green make
yellow; green and blue make cyan.
Colour
44
To find north we use a compass. The
compass needle points to magnetic north
because it is a magnet. The tip of the
needle which points north is called the
north-seeking pole or N pole, and the
other is called the south-seeking pole.
Magnetism
45
A magnetic field is the force that
surrounds a permanent magnet. The N
Pole of one magnet is attracted to the
S Pole of the other. This is because
unlike poles attract and like poles
repel.
Magnetism
46
If you rub a glass rod with a piece
of silk, the rod acquires a charge.
The electric charges resting in
the glass rod, or in a comb or any
other object, are known as static
electricity.
Electric Charge
47
The flow of electrons takes place
where there is a difference in
potential between two conductors.
This potential difference (p.d.) is
measured in volts, and is often called
the voltage.
Electric Charge
48
As a result of chemical reactions, a
cell produces a given number of volts.
This is the cell's electromotive force
or e.m.f. When a cell causes a flow of
electrons through a circuit, there is
an electric current in the circuit.
Electric Current
49
The strength of an electric current,
the amount of charge which passes in a
unit of time, is measured in amperes.
The current in a wire is proportional
to the potential difference between
the ends of the wire.
Electric Current
50
Certain elements, e.g. radium and
polonium, are unstable and radioactive;
they continuously emit particles at
high velocities. Each radioactive
element has a fixed rate of decay
which is called its half-life.
Radioactivity
1
Matter exists in three states: solid,
liquid and gas. A solid, for example
a stone, has a definite shape and a
definite volume. A liquid, such as
oil, has a definite volume but no
definite shape.
Matter
2
A gas, e.g. hydrogen, has neither
definite shape nor definite volume.
Water can exist in all three states:
below 0 degrees celsius it is a
solid (ice). Between 0 and 100 degrees
celsius it is a liquid (water).
Matter
3
Above 100 degrees water becomes a gas
(vapour). All matter consists of
elements such as zinc or oxygen, or
of compounds such as nitric acid or
sulphur dioxide. The smallest particle
of an element is called an atom.
Matter
4
The smallest particle of a compound is
called a molecule. A molecule of
sulphur dioxide is a compound of one
atom of sulphur and two atoms of
oxygen. A molecule of water is two
atoms of hydrogen and one of oxygen.
Molecules
5
When we measure quantities of matter,
we may use the fundamental units of
time (e.g. the second), mass (e.g. the
kilogram) and length (e.g. the metre).
We may also use units such as area,
volume or density.
Measurements
6
The area of a rectangle is found by
multiplying the length by the width.
The volume of a cylinder is equal to
Pi times the radius squared times the
height. The density of a substance
equals the mass divided by the volume.
Measurements
7
We use the terms specific gravity or
relative density to indicate density
relative to water. Gold has a density
of 19.3 grams per cubic centimetre.
So one cubic cm of gold has 19.3 times
the mass of 1 cubic cm of water.
Specific Gravity
8
A liquid takes the shape of the
container in which it rests. It also
pushes sideways against the sides, and
downwards on the bottom of the
container, and upwards against anything
placed in it.
Liquids
9
The existence of the force which is
exerted upwards is called buoyancy.
The law on buoyancy states: An object
immersed in a liquid appears to lose an
amount of weight which is equal to the
weight of the liquid it displaces.
Buoyancy
10
A stone with a mass of 3.2 kg is
suspended from a spring balance and
lowered into some water. The spring
balance now reads 2.2 kg, indicating
that the stone has displaced 1 kg (or
one litre of water).
Buoyancy
11
The Earth's atmosphere, the air we
breathe, consists of a mixture of
gases. Air has mass and exerts
pressure. At sea level, this pressure
is sufficient to support a 76 cm column
of mercury in a vacuum tube.
Gases
12
Changes in the weather cause small
changes in the atmospheric pressure.
A barometer is the instrument used to
measure these changes. The aneroid
barometer consists of a vacuum cell
attached by levers to a pointer.
Gases
13
The greater the pressure that is
applied to a gas, the less space it
will occupy. Boyle's law states: If
the temperature of a fixed mass of gas
remains constant, the volume will be
inversely proportional to the pressure.
Gases
14
Charles' Law and the Pressure Law also
describe the relationship between the
temperature, pressure and volume of a
gas. If one of the 3 values is
constant, the other 2 values are found
to be in direct or inverse proportion.
Gases
15
If a quantity has magnitude (size or
amount) and direction, it is a vector
quantity. If it has magnitude but no
direction, it is a scalar quantity.
Force is a vector quantity. Gravity is
an example of a force.
Force
16
Newton's law of gravity states that:
The force of attraction which exists
between two bodies is directly
proportional to their masses, and
inversely proportional to the square
of the distance between them.
Gravity
17
The Earth's gravity pulls downwards on
every particle of a body with a force
equal to the weight of that particle.
The sum of these forces appears to act
through the centre of gravity of the
body.
Gravity
18
If a body is not at rest, it is in
motion. The rate at which the body is
moving is called its speed. Speed is
calculated by dividing the distance by
the time (v = s/t) and is therefore a
derived unit.
Motion
19
The term velocity is used to mean speed
in a given direction. It is therefore
a vector quantity. If we multiply the
mass of a body by its velocity, we
obtain its momentum. The formula for
this is M = mv.
Motion
20
The rate at which the velocity of a
body changes is called acceleration,
and acceleration is calculated by
dividing the change in velocity by
the time taken. Acceleration is often
expressed in metres per second squared.
Motion
21
Work is done when a force moves a load
over a certain distance. The capacity
to do work is called energy. Energy,
like work is measured in joules. It
is a scalar quantity, having magnitude
but no direction.
Work & Energy
22
Mechanical energy exists in two forms:
a) kinetic energy, the energy a body
possesses because of its motion, and
b) potential energy, the energy a body
possesses because of its position or
state.
Work & Energy
23
The rate at which work is done is
power. This is expressed by the
formula P = W/t, where W is the amount
of work done or energy expended, t is
the time taken and P is the power.
One joule per second is a watt.
Power
24
In a hydro-electric power station, the
potential energy of the water behind
the dam is converted into electrical
energy. The water falls with great
force through pipes. This provides the
kinetic energy to drive the turbines.
Power
25
In general, when heat is applied to a
substance, its temperature rises. The
change in temperature can be measured
by a thermometer. When heated, most
substances expand, and they contract
when cooled.
Heat
26
Different substances have different
coefficients of expansion, i.e. they
expand by different amounts when
exposed to the same change in
temperature. E.g. lead has a higher
coefficient of expansion than concrete.
Heat
27
Heat may be transmitted in three ways.
The first is by conduction through a
material, which takes place, for
example, when one end of a copper tube
is heated and the heat is conducted to
to the other end.
Heat
28
Heat is also transmitted by convection
through the movements of a liquid or
gas, such as when warm air passes from
one part of a building to a higher part
of the building. Another way is by
radiation of heat waves.
Heat
29
Poor conductors of heat are good
insulators, and a vacuum is the best
insulator. The common thermos or
vacuum flask, in which we may keep food
hot or cold, is designed according to
this principle.
Heat
30
Some materials can absorb and give off
much more heat than others. For
example, if a piece of iron and a piece
of lead of equal size are heated to the
same temperature and left to cool, the
lead will cool much more quickly.
Heat
31
The specific heat of a substance is the
heat required to raise the temperature
of unit mass of that substance
through one degree celsius. Heat
used to be measured in calories, but
the modern unit is the joule.
Heat
32
Heating a substance does not always
raise its temperature. If we heat
crushed ice, the ice changes to water
but the temperature remains the same.
Also the temperature of boiling water
does not rise when heated further.
Heat
33
All pure substances change their states
at fixed temperatures, the melting
point and the boiling point. The heat
which changes the state without
changing the temperature is called
latent heat.
Heat
34
Sound waves are waves of compression.
This means that they require a medium
through which to travel. As the waves
pass through the medium, the particles
of the medium vibrate or oscillate.
Sound cannot travel through a vacuum.
Sound
35
Sound waves will travel through solids,
liquids and gases. Sound waves travel
at a speed of 340 metres per second
through air, through water at 1,450
metres per second and through iron at
5,125 metres per second.
Sound
36
As waves pass through a medium, the
maximum amount that a particle of the
medium moves is called the amplitude of
the wave. The amplitude depends on the
quantity of energy carried by the wave.
Wavelengths are measured in metres.
Wave Motion
37
The number of complete vibrations or
oscillations in each second is the
frequency of the wave. Wave frequency
is measured in hertz. It follows that
the wave speed is the product of the
wavelength and the wave frequency.
Wave Motion
38
Light radiation, like the radiation of
heat or radio waves, is an example of
electromagnetic radiation. Light
travels much faster than sound, at a
speed of around 300,000 km/s, and light
rays travel in straight lines.
Light
39
When light moves from one medium to
another, e.g. from air to water, the
rays change direction. We call this
refraction and say that the rays are
refracted. The refraction depends on
the refractive index of the medium.
Light
40
Lenses are used to control the
refraction of light. A converging
lens is one which causes the light
rays to come together and a diverging
lens is one which causes the light
rays to spread out.
Lenses
41
When parallel light rays strike a
diverging lens, they appear to come
from a point on the same side as the
source of the light. This point is the
virtual focus. A short-sighted person
needs glasses with diverging lenses.
Lenses
42
White light consists of a mixture of
colours. In a vacuum all these colours
travel at the same speed, but in matter
their speeds are slightly different.
Therefore we can use a prism to make
the colours disperse.
Colour
43
Any colour can be produced by using the
correct proportions of red, green and
blue light. These are therefore known
as the primary colours. Red and blue
produce magenta; red and green make
yellow; green and blue make cyan.
Colour
44
To find north we use a compass. The
compass needle points to magnetic north
because it is a magnet. The tip of the
needle which points north is called the
north-seeking pole or N pole, and the
other is called the south-seeking pole.
Magnetism
45
A magnetic field is the force that
surrounds a permanent magnet. The N
Pole of one magnet is attracted to the
S Pole of the other. This is because
unlike poles attract and like poles
repel.
Magnetism
46
If you rub a glass rod with a piece
of silk, the rod acquires a charge.
The electric charges resting in
the glass rod, or in a comb or any
other object, are known as static
electricity.
Electric Charge
47
The flow of electrons takes place
where there is a difference in
potential between two conductors.
This potential difference (p.d.) is
measured in volts, and is often called
the voltage.
Electric Charge
48
As a result of chemical reactions, a
cell produces a given number of volts.
This is the cell's electromotive force
or e.m.f. When a cell causes a flow of
electrons through a circuit, there is
an electric current in the circuit.
Electric Current
49
The strength of an electric current,
the amount of charge which passes in a
unit of time, is measured in amperes.
The current in a wire is proportional
to the potential difference between
the ends of the wire.
Electric Current
50
Certain elements, e.g. radium and
polonium, are unstable and radioactive;
they continuously emit particles at
high velocities. Each radioactive
element has a fixed rate of decay
which is called its half-life.
Radioactivity