Force
Any action which causes full or push on a body is called force. Forces are used
in our everyday actions like pushing, pulling, lifting, stretching, twisting,
pressing.
Force is a vector quantity, it's SI unit is Newton and the CGS unit is dyne.
For example
A force is used when we kick a football ,we lift a box from the floor, we stretch a
rubber band etc
Fundamental or basic forces in nature
Gravitational forces every object in the universe attracts each other, this force of
attraction is called gravitational force.
Electromagnetic forces are the forces between charged particles. When the
charges are at rest the forces are called electrostatic forces. the forces between
unlike charges are attractive and the forces between like charges are repulsive.
Types of forces
Balanced forces When The net effect produced by a number of forces acting on
a body is zero then the forces are said to be balanced forces balanced forces
can only bring a change in the shape of the body example if the block is pulled
from both the sides with equal forces the block will not move ,such forces are
called balanced forces.
Unbalanced Forces when the net effect produced by a number of forces on a
body is non zero, then the forces are said to be unbalanced forces.
Inertia
The property of an object to resist any change in its state of motion along a
straight line or rest is called inertia.
There are types of inertia.
Inertia of rest if an object resists the change in its state of rest its inertia is called
inertia of rest.
Inertia of motion if an object resists the change in its state of motion it's inertia
is called inertia of motion.
Inertia of direction if an object resists the change in direction of its motion it's
inertia is called inertia of direction.
Newton's laws of motion
Laws of motion was propounded by Sir Isaac Newton in 1687 in his book
Principia. There are three laws of motion.
Newton's first law of motion
Every body retains its state of rest or state of motion along a straight line until
an external force is applied on it. This law is also known as law of inertia.
Momentum
The momentum of a moving body is equal to the product of its mass and its
velocity it is a vector quantity having SI unit kg meter per second.
For example
A much greater force is required to push a truck then a car to bring them to the
same speed in the same time because due to higher mass heavy body requires
higher momentum similarly a greater force is required to stop a heavy body than
a light body in the same time.
Law of conservation of momentum
If no external force acts upon asystem of two or more bodies then the total
momentum of the system remains constant. This is called the law of
conservation of momentum.
Newton's second law of motion
The second law of motion states that the rate of change of momentum of an
object is proportional to the applied unbalanced force in the direction of force.
According to Newton's second law
Example
When of fast moving cricket ball hits a spectator it may hurt him because the
speed of cricket ball is higher due to which is acceleration is also higher.
Cricket player moves his hand backwards on catching a fast cricket ball because
the cricket player increases the time during which the high velocity of moving
ball decreases to 0 does the acceleration of ball is decreased and therefore the
impact of catching the fast moving wall is also reduced if the ball is stopped
suddenly then it's high velocity decreases to 0 in a very short interval of time
does the rate of change of momentum of the wall will be large therefore a large
force would have to be applied for holding the catch that may hurt the palm of
the player.
Newtons third law of motion
For every action there is an equal and opposite reaction and both acts on two
different bodies so this law is also known as law of action and reaction.
Some phenomenons based on Newton's third law of motion.
It is difficult to walk on sand because on pushing send gets displaced and
reaction from Sandy ground is small.
A swimmer pushes the water backwards (action) with a force . The water pushes
the swimmer forward ( reaction) with the same force . Hence the swimmers
swims.
