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A force is a push or pull acting upon an
object as a result of its interaction with
Contact Forces-resulted from the contact of
two interacting bodies.
Action at a Distance Forces-resulted from the
non-contact of two interacting bodies.
Normal Force- The normal force is the support
force exerted upon an object that is in contact
with another stable object. For example, if a
book is resting upon a surface, then the surface
is exerting an upward force upon the book in
order to support the weight of the book. On
occasions, a normal force is exerted horizontally
between two objects that are in contact with each
other. For instance, if a person leans against a
wall, the wall pushes horizontally on the person.
Tension Force-The tension force is the force
that is transmitted through a string, rope,
cable or wire when it is pulled tight by forces
acting from opposite ends. The tension force
is directed along the length of the wire and
pulls equally on the objects on the opposite
ends of the wire.
Spring Force-The spring force is the force
exerted by a compressed or stretched spring
upon any object that is attached to it. An
object that compresses or stretches a spring
is always acted upon by a force that restores
the object to its rest or equilibrium position.
For most springs (specifically, for those that
are said to obey "Hooke's Law"), the
magnitude of the force is directly
proportional to the amount of stretch or
compression of the spring.
Frictional Force-The friction force is the force exerted by a
surface as an object moves across it or makes an effort to
move across it. There are at least two types of friction
force - sliding and static friction. Though it is not always
the case, the friction force often opposes the motion of an
object. For example, if a book slides across the surface of
a desk, then the desk exerts a friction force in the
opposite direction of its motion. Friction results from the
two surfaces being pressed together closely, causing
intermolecular attractive forces between molecules of
different surfaces. As such, friction depends upon the
nature of the two surfaces and upon the degree to which
they are pressed together. The maximum amount of
friction force that a surface can exert upon an object can
be calculated using the formula below:
Ffrict = µ • Fnorm
Air Resistance Force-The air resistance is a
special type of frictional force that acts upon
objects as they travel through the air. The force
of air resistance is often observed to oppose the
motion of an object. This force will frequently be
neglected due to its negligible magnitude (and
due to the fact that it is mathematically difficult
to predict its value). It is most noticeable for
objects that travel at high speeds (e.g., a skydiver
or a downhill skier) or for objects with large
Applied Force-An applied force is a force that
is applied to an object by a person or another
object. If a person is pushing a desk across
the room, then there is an applied force
acting upon the object. The applied force is
the force exerted on the desk by the person.
Bouyant Force-the upward force exerted by a
fluid on a submerged or floating object. The
bouyant force is equal to the displaced fluid
Gravitational Force-The force of gravity is the
force with which the earth, moon, or other
massively large object attracts another object
towards itself. By definition, this is the weight of
the object. All objects upon earth experience a
force of gravity that is directed "downward"
towards the center of the earth. The force of
gravity on earth is always equal to the weight of
the object as found by the equation:
Fgrav = m * g
where g = 9.8 N/kg (on Earth)
and m = mass (in kg)
Magnetic Force-Magnetic force is the
attraction or repulsion that arises between
electrically charged particles because of their
motion. It is the basic force responsible for
the action of electric motors and the
attraction of magnets for iron.
Electrical Forces-Electrical force is the force
that exists between all charged particles. The
electric force is responsible for such diverse
phenomena as making your hair stand up on
a cold dry day, creating chemical bonds, and
allowing you to see when you turn on a lamp
on a dark night.
The Strong Force
This force is responsible for binding of nuclei. It is
the dominant one in reactions and decays of most of
the fundamental particles. This force is so strong that
it binds and stabilize the protons of similar charges
within a nucleus. However, it is very short range. No
such force will be felt beyond the order of 1 fm
(femtometer or 10-15 m).
The Electromagnetic Force
This is the force which exists between all particles which
have an electric charge. For example, electrons (negative
charge) bind with nucleus of an atom, due to the presence
of protons (positive charge). The force is long range, in
principle extending over infinite distance. However, the
strength can quickly diminishes due to shielding effect.
Many everyday experiences such as friction and air
resistance are due to this force. This is also the resistant
force that we feel, for example, when pressing our palm
against a wall. This is originated from the fact that no two
atoms can occupy the same space. However, its strength is
about 100 times weaker within the range of 1 fm, where
the strong force dominates. But because there is no
shielding within the nucleus, the force can be cumulative
and can compete with the strong force. This competition
determines the stability structure of nuclei.
Weak Force This force is responsible for
nuclear beta decay and other similar decay
processes involving fundamental particles.
The range of this force is smaller than 1 fm
and is 10-7 weaker than the strong force.
Nevertheless, it is important in understanding
the behavior of fundamental particles.
The Gravitational Force
This is the force that holds us onto the Earth. It could be important in
our daily life, but on the scale of atomic world it is of negligible or no
importance at all. Gravitational force is cumulative and extended to
infinity. It exists whenever there is matter. Your body is experiencing a
gravitaional pull with, say, your computer (or anything close to you or as
far away as stars and galaxies) but the effect is so small you will never
sense it. However, you can sense the gravitaional pull with the Earth
(that is, your weight) due to the cumulative effect of billions of billions of
the atoms made up your body with those atoms of the Earth. This means
that the larger the body (contain more matter), the stronger the force.
But on the scale of individual particles, the force is extremely small, only
in the order of 10-38 times that of the strong force.
The gravitational force between two masses is
This formula represents the Universal Law of
Gravitation and G is the universal gravitation
constant. It means that force is directly
proportional to the product of two masses
and inversely proportional to the square of
the distance between two masses, which is
denoted by r.
Weight is the force due to gravity. It is the
force that pulls the object downwards the
center of the earth. The formula for the
2. Strong Nuclear Force
-It is a binding force between two nucleons (neutrons and
protons). This is the force that is responsible for holding
two nucleons together to form nuclei. The characteristics of
strong nuclear force are as follows:
Charge independence-The nuclear force betwen two
protons is the same as between two neutrons and between a
neutron and a proton.
Saturation-The force needed to tear a neutron from a
nucleus is approximately the same regardless of the number
of nucleons in the nucleus.
Short range-The force decreases rapidly with increasing
distance. At a distance of about 1 femtometer (1 fm-10-15
meter) the strong nuclear forc is attractive (about 10 times the
electric force between protons). The force force becomes
repulsive when two nucleons are about 0.4 fm from each
other. The nuclei do not collapse.
3. Electromagnetic Force
It is a force between particles with electric charges. It can
either be attractive or repulsive. Its strength is 100 times
weaker within the range of 2 fm. This phenomenon has two
Electrostatic force-is the force of two electrically charged
particles exerted on one another. This force between two
charges is directly proportional to the product of the
magnitude of the charges and inversely proportional to the
square of the distance separating the charges. This is a law
is known as Coulombs Law:
Magnetic force-is the force due to motion of charges. The
strength of interaction depends on the separating the two
4. Weak nuclear force
It is the force responsible for beta decay and other
decay process involving fundamental processes. It is
the interaction between all leptons, which includes
electrons, positrons, muons and neutrons and
hadrons. Weak force involves the exchange of the
immediate vector bosons, the W and the Z. All leptons
and hadrons interact via this force.
First Law: Law of Inertia
◦ An object at rest will remain at rest unless acted on
by an unbalanced force. An object in motion
continues in motion with the same speed and in the
same direction unless acted upon by an unbalanced
This means that there is a natural tendency of
objects to keep on doing what they're doing. All
objects resist changes in their state of motion. In
the absence of an unbalanced force, an object in
motion will maintain this state of motion.
Second Law: Law of Acceleration
Acceleration is produced when a force acts on
a mass. The greater the mass (of the object
being accelerated) the greater the amount of
force needed (to accelerate the object).
Everyone knows that heavier objects require more
force to move the same distance as lighter objects.
Second Law gives us an exact relationship
between force, mass, and acceleration. It can
be expressed as a mathematical equation:
FORCE = MASS times ACCELERATION
This is an example of how Newton's Second
Mike's car, which weighs 1,000 kg, is out of
gas. Mike is trying to push the car to a gas
station, and he makes the car go 0.05 m/s/s.
Using Newton's Second Law, you can compute
how much force Mike is applying to the car.
Answer = 50 newtons
Momentum-It is also known as mass in
motion. It is the product of the mass and the
velocity of a body. The formula for
Where: m is mass, v is velocity and P is
Impulse –is the change in momentum
Third Law: Law of Interaction
For every action there is an equal and
This means that for every force there is a
reaction force that is equal in size, but
opposite in direction. That is to say that
whenever an object pushes another object it
gets pushed back in the opposite direction
The rocket's action is to push down on the
ground with the force of its powerful engines,
and the reaction is that the ground pushes
the rocket upwards with an equal force.
refers to an activity involving a force and movement in the
directon of the force. A force of 20 newtons pushing an object 5
meters in the direction of the force does 100 joules of work.
is the capacity for doing work. You must have energy to
accomplish work - it is like the "currency" for performing work.
To do 100 joules of work, you must expend 100 joules of
is the rate of doing work or the rate of using energy, which are
numerically the same. If you do 100 joules of work in one second
(using 100 joules of energy), the power is 100 watts.
Work is the product of the applied force in
the direction of motion and the displacement
through which the force acts. That is
If the applied force is not in the direction of the
motion, only the part of the displacement
parallel to the force’s direction is important.
Thus, when the applied force is not in the
direction of the motion the work done is
The relationship between the force applied to a spring and the
amount of stretch was first discovered in 1678 by English
scientist Robert Hooke. As Hooke put it: Ut tensio, sic vis.
Translated from Latin, this means "As the extension, so the
force." In other words, the amount that the spring extends is
proportional to the amount of force with which it pulls. If we had
completed this study about 350 years ago (and if we knew some
Latin), we would be famous! Today this quantitative relationship
between force and stretch is referred to as Hooke's law and is
often reported in textbooks as
Fspring = -k•x
where Fspring is the force exerted upon the spring, x is the
amount that the spring stretches relative to its relaxed position,
and k is the proportionality constant, often referred to as the
spring constant. The spring constant is a positive constant
whose value is dependent upon the spring which is being
The work done in compressing or extending
the spring by an applied force is
Where x is the distance the spring has been
compressed or extended from its equilibrium
The quantity that has to do with the rate at which a certain
amount of work is done is known as the power. The hiker has a
greater power rating than the rock climber.Power is the rate at
which work is done. It is the work/time ratio. Mathematically, it
is computed using the following equation.
Power = Work / time
P = W / t
The standard metric unit of power is the Watt. As is implied by
the equation for power, a unit of power is equivalent to a unit of
work divided by a unit of time. Thus, a Watt is equivalent to a
Joule/second. For historical reasons, the horsepower is
occasionally used to describe the power delivered by a machine.
One horsepower is equivalent to approximately 750 Watts.
Energy, in physics, the capacity for
doing work. It may exist in potential, kinetic,
thermal, electrical, chemical, nuclear, or other
various forms. There are, moreover, heat and
work—i.e., energy in the process of transfer
from one body to another. After it has been
transferred, energy is always designated
according to its nature. Hence, heat
transferred may become thermal energy,
while work done may manifest itself in the
form of mechanical energy.
Mechanical Energy is the energy of motion that does
the work. An example of mechanical energy is the
wind as it turns a windmill.
Heat energy is energy that is pushed into motion by
using heat. An example is a fire in your fireplace.
Chemical Energy is energy caused by chemical
reactions. A good example of chemical energy is food
when it is cooked.
Electrical Energy is when electricity creates motion,
light or heat. An example of electrical energy is the
electric coils on your stove.
Gravitational Energy is motion that is caused by
gravity. An example of gravitational energy is water
flowing down a waterfall.
Energy exists in many different forms.
Examples of these are: light energy, heat
energy, mechanical energy, gravitational
energy, electrical energy, sound energy,
chemical energy, nuclear or atomic energy
and so on. These forms of energy can be
transferred and transformed between one
another. This is of immense benefit to us. For
a source of energy to end up as electricity it
may undergo many transformations before it
can power the light bulb in your home.
Kinetic energy is the energy in moving
objects or mass. Wind energy is an example.
The molecules of gas within the air, are
moving giving them kinetic energy.
Potential energy is any form of energy that
has stored potential that can be put to future
For example, water stored in a dam for hydroelectricity
generation is a form of potential energy. When valves are
opened the force of gravity cause water to begin to flow.
The gravitational potential energy of the water is
converting to kinetic energy. The flowing water can turn a
turbine, which will further convert the kinetic energy of the
water into useable mechanical energy. An alternator or
generator then converts the mechanical energy from the
turbine into electrical energy. This electricity is then sent
to the electricity grid and to our homes where it is
converted into light energy (lights and televisions), sound
energy (televisions, stereos), heat energy (hot water,
toasters, ovens), mechanical energy (fans, vacuum
cleaners, fridge and air conditioner compressors) and so
Gravitational potential energy is energy an object
possesses because of its position in a gravitational
field. The most common use of gravitational potential
energy is for an object near the surface of the Earth
where the gravitational acceleration can be assumed
to be constant at about 9.8 m/s2. Since the zero of
gravitational potential energy can be chosen at any
point (like the choice of the zero of a coordinate
system), the potential energy at a height h above that
point is equal to the work which would be required to
lift the object to that height with no net change
in kinetic energy. Since the force required to lift it is
equal to itsweight, it follows that the gravitational
potential energy is equal to its weight times the
height to which it is lifted.
Thus the formula for the gravitational potential
Where PE is the gravitational potential energy,
m is the mass of the body, g is the
gravitational acceleration and h is the vertical
distance, w is the weight of the body.
Mechanical energy is the sum of the potential
and kinetic energies in a system. The
principle of the conservation of mechanical
energy states that the total mechanical
energy in a system (i.e., the sum of the
potential plus kinetic energies) remains
constant as long as the only forces acting are
conservative forces. We could use a circular
definition and say that a conservative force as
a force which doesn't change the total
A good way to think of conservative forces is to consider
what happens on a round trip. If the kinetic energy is the
same after a round trip, the force is a conservative force,
or at least is acting as a conservative force. Consider
gravity; you throw a ball straight up, and it leaves your
hand with a certain amount of kinetic energy. At the top of
its path, it has no kinetic energy, but it has a potential
energy equal to the kinetic energy it had when it left your
hand. When you catch it again it will have the same kinetic
energy as it had when it left your hand. All along the path,
the sum of the kinetic and potential energy is a constant,
and the kinetic energy at the end, when the ball is back at
its starting point, is the same as the kinetic energy at the
start, so gravity is a conservative force.
A source of energy is that which is capable of
providing enough useful energy at a steady rate
over a long period of time. A good source of
energy should be : i) Safe and convenient to use,
e.g., nuclear energy can be used only by highly
trained engineers with the help of nuclear power
plants. It cannot be used for our household
purposed. ii) Easy to transport, e.g., coal, petrol,
diesel, LPG etc. Have to be transported from the
places of their production to the consumers. iii)
Easy to store, e.g., huge storage tanks are
required to store petrol, diesel, LPG etc.
Characteristics of an ideal or a good fuel:
1. It should have a high calorific or a heat value, so that it
can produce maximum energy by low fuel consumption.
2. It should have a proper ignition temperature, so that it
can burn easily.]
3. It should not produce harmful gases during combustion.
4. It should be cheap in cost and easily available in plenty
5. It should be easily and convenient to handle, store and
transport from one place to another.
6. It should not be valuable to any other purpose than as a
7. It should burn smoothly and should not leave much
residue after its combustion.
The sources of energy can be classified as follows
1. Renewable sources of energy :- Renewable
sources of energy are those which are
inexhaustible, i.e., which can be replaced as we
use them and can be used to produce energy
again and again. These are available in an
unlimited amount in nature and develop within a
relatively short period of time.
Examples of Renewable Sources of Energy. (i)
Solar energy, (ii) Wind Energy, (iii) water
energy (hydro-energy), (iv) geothermal
energy, (v) ocean energy, (vi) biomass energy
(firewood, animal dung and biodegradable
waste from cities and crop residues constitute
Advantages of Renewable Sources of Energy :
(i) These sources will last as long as the Earth
receives light from the sun.
(ii) These sources are freely available in
(iii) These sources do not cause any pollution.
2. Non-renewable sources of energy are
those which are exhaustible and cannot be
replaced once they have been used. These
sources have been accumulated in nature
over a very long period of million of years.
Examples of Non-renewable sources of
Energy : (i) Coal (ii) Oil and (iii) Natural gas.
All these fuels are called fossil fuels.
(i) Due to their extensive use, these sources
are fast depleting.
(ii) It is difficult to discover and exploit new
deposits of these sources.
(iii) These sources are a major cause of
Sources of energy are also classified as :
(i) Conventional sources of energy
(ii) Nonconventional sources of energy.
Conventional sources of energy : Are those which
are used extensively and a meet a marked
portion of our energy requirement and these are
: (a) Fossil fuels (coal, oil and natural gas) and (b)
Hydro energy (energy of water flowing in rivers).
Biomass energy and wind energy also fall in this
category as these are being used since ancient
Non-conventional sources of energy : Are those
which are not used as extensively as the
conventional ones and meet our energy
requirement only on a limited scale. Solar energy,
ocean energy (tidal energy, wave energy, ocean
thermal energy, OTE), Geothermal energy and
nuclear energy belong to this category. These
sources of energy which have been tapped with
the aid of advances in technology to meet our
growing energy needs are also called alternative
sources of energy.
Wind Energy: -When large masses of air move from one
place to another it is referred to as wind. During this
process kinetic energy gets associated with it which is
referred to as wind energy.
Principle of utilisation of wind energy: - Wind energy is
efficiently converted into electrical energy with the aid of a
windmill. A windmill is a large fan having big blades,
which rotate by the force exerted by moving wind on
them. These blades remain continuously rotating as long
as wind is blowing and can be used to drive a large
number of machines like water pumps, flour mills etc. But
these days a windmill is used to generate electric current
which is used for various purposes and therefore wind
power stations are established all over the world which
convert wind energy directly into electrical energy.
The important uses of wind energy are;
1. It is used to drive windmills, water lifting
pumps and flour mills etc.
2. It is used to propel sale boats.
3. It is used to fly engine less aeroplanes or
gliders in the air.
4. It is used to generate electricity used for
various purposes like lightening, heating
Temperature- hotness or coldness of body
Thermometer-is a device used to measure
Thermal equilibrium- one system is said to
be in thermal equilibrium with another
system if their temperatures are the same.
Thermal energy-is the amount of energy
measured with a thermometer. It represents
the collective kinetic energy of the molecules
moving within a substance.
Galelian thermometer- a glass bulb with a long
stem and submerged the end of the stem in
Bimetallic strip- two different thin strips of metal
riveted together and spiraled, the outer end
anchored to the thermometer case and the inner
end attached to the pointer. The pointer rotates
in response to change in temperature.
Optical pyrometer- measures intensity of
radiation emitted by red hot or white hot