Mechanics and Properties of Matter

Mechanics is the study of motion of bodies or objects 

Whats motion?

When a body tries to change its position from one place to other with respective time, we say that the body is in motion.

• There are two types of motion:

1. Linear motion

2. Rotational motion

Linear motion: A person walking on the floor is a linear motion

Rotational motion: The motion of a top,spinning on its axis is rotational

Distance: The space between two points is called distance

Displacement: The shortest distance covered by a body is called displacement

Speed: The distance covered by a body per unit time is known as speed

   Speed = distance travelled/time period

units: metre/second i.e m/s     

Velocity: The rate of change of displacement per unit time is called velocity

units: The SI unit for velocity is metre/second i.e m/s

Speed vs Velocity: The difference between speed and time is speed is the distance between two points where as the velocity is distance travelled by a body in a specific direction.

Acceleration: Velocity of a body changes due to speed or direction or both.The rate of change of velocity of a body is called acceleration.

Acceleration = change in velocity / time

Acceleration due to gravity: it is defined as the rate of change of acceleration due to gravity  i.e the value of acceleration due to gravity(g)  on the surface of the earth is about 9.8 m/s^2

Ex: When a body is freely falling from 10th floor and the other body is falling from 5th floor the velocity of 10th floor body is more than that of 5th floor i.e the velocity increases every second by 9.8m/s.

Force: A force is just a push or pull which changes the bodies state of rest or uniform motion in a straight line.

Gravitational force: The force which attracts everything towards the earth is known as gravitational force, in fact there is gravitational force between all bodies.

 Newton's law of universal gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to their masses and inversely proportional to the square of the distance between them.

it is given by→ F= G m1*m2/r^2

where 'r' is the distance between two bodies of masses 'm1' and 'm2' respectively


Centripetal Force: If  a body is moving in a circular motion there must be a force which is directing it towards its centre, this is known as centripetal force.

Its given by F=mv^2/r

Centrifugal Force:The force which acts outwards to a body which is moving in a circular motion,its not a real force however it is used to explain some of the theories successfully.

Weight: The weight of a body is the force with which the earth attracts the body towards its centre where as the mass is the quantity of matter contained in a body.

W=mg(m=mass,g=gravity)

Friction: It is a force which opposses the relative motion of two surfaces to be in contact.

Newton's laws of motion: There are three laws given by newton on the account of motion

First law: Every body continues to be in rest or uniform motion until a net applied on it.

Second law:The rate of change of momentum of a body is equal to force applied on it(F=ma).

Third law: Every action has an equal and opposite reaction

work:If a force produces change in motion and can be calculated by the product of force and displacement then its known as work.It is given by W=F.S,units: Joule's

Power: The work done per unit time is known as power units: watt

Energy: The capacity to do work is known as energy units: joule

Kinetic energy:The energy possessed by a body due to its motion is called kinetic energy and its given by KE=mv^2/2

Potential energy: The energy possessed by a body by the virtue of its position is called potential energy PE=mgh

Conservation of energy: As energy can neither be created nor destroyed but can be transformed from one form to another the total energy remains constant

Centre of gravity:A point at which a body's whole weight is acted upon is called centre of gravity.

Escape velocity: The velocity required to go beyond earth's garvitational field is called escape velocity i.e 11.2km/s or 25k miles/hr or in other words the body would not return to earth's surface.

Density: The mass per unit volume of a body or substance is called as density 
units: kg/m^3.

Relative density: It is defined as the ratio of density of a substance to the density of water,it doesn't have units.

Pressure: It is defined as the force per unit area P=f/a units: Nm/m^2

Pressure in liquids: The pressure at any point in a liquid acts in all directions P=hpg

Atmospheric pressure: The air surrounding the earth is known as atmosphere.

Archimedes principle: If a body is completely or partially immersed in a liquid it experiences a upward thrust which is equal to the weight of the fluid displaced

Matter: A matter is something which occupies space.it consists of atoms and molecules.

Molecule: It is the smallest particle of a substance which has all its physical and chemical properties.

Atom: It is a smallest particle which has chemical propertities of their own.

Diffusion: It is a mixture of gases,liquid's and solids

Surface tension: The tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area is called surface tension.

Capillarity:When a clean glass tube having a small diameter is dipped in water then the water cleans the tube this is known as capillarity

Adhessive force: The force of attraction between unlike molecules is known as adhessive force

Cohessive force: The force of attraction between like molecules is known as cohessive force