# Physics Notes – Important Definitions and Laws – Static Science GK Material for Competitive exams

### Important Definitions and Laws of Physics

WORK – If a body gets displaced when a force acts on it, work is said to be done. Work is measured by product of force and displacement of the body along the direction of force.
⦁ Work is scalar quantity and its SI unit is joule.
⦁ ENERGY – Capacity of doing work by a body is called its energy.
⦁ Energy is a scalar quantity and its SI unit is joule.
⦁ POTENTIAL ENERGY – The capacity of doing work developed in a body due to its position or configuration is called its potential energy.
⦁ KINETIC ENERGY – Energy possessed by a body due its motion is called Kinetic Energy of the body. If the body of mass m is moving with speed v, then kinetic energy of the body is half mv square.
⦁ GRAVITATION – Every body attracts other body by a force called force of gravitation.
⦁ NEWTONS LAW OF GRAVITATION – The force of gravitational attraction between two point bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
⦁ GRAVITY – The gravitational force of earth is called gravity i.e. gravity is the force by which earth pulls a body towards its centre.
⦁ The value of g on moon is less than that on earth.Hence on moon, a man can jump higher than earth.
⦁ The orbital speed of a satellite revolving near the surface of earth is 7.9km/sec.
⦁ ESCAPE VELOCITY – Escape velocity is that minimum velocity with which a body should be projected from the surface of earth and never return to earth.
⦁ For earth, escape velocity = 11.2 km/s.
⦁ PRESSURE – Pressure is defined as force acting normally on unit area of the surface.
⦁ Pressure = F/A
⦁ SI unit of pressure is Newton per metre square also called pascal(Pa). Pressure is a scalar quantity.
⦁ ATMOSPHERIC PRESSURE – Atmospheric pressure is that pressure which is exerted by a mercury column of 76 cm length at 0 degree Celsius at 45 degree latitude at the sea-level.
⦁ ARCHIMEDES PRINCIPLE – When a body is immersed partly or wholly in a liquid, there is an apparent loss in weight of the body which is equal to the weight of liquid displaced by the body.
⦁ DENSITY – Density is defined as mass per unit volume.
⦁ Density = Mass/Volume. Its Si unit is Kilogram per meter square.
⦁ Relative density is measured by Hydrometer.
⦁ Purity of milk is measured by Lactometer.
⦁ COHESIVE FORCE – The force of attraction between the molecules of same substance is called cohesive force. Cohesive force is maximum in solids. This is why solids have a fixed shape. Cohesive force is negligible in case of gases.
⦁ ADHESIVE FORCE – Force of attraction between the molecules of different substances is called adhesive force. Due to adhesive force one body sticks to other.
⦁ SURFACE TENSION – Surface tension is the virtue of which it has the tendency to have the area of its free surface minimum as if it were under tension like a stretched elastic membrane.
⦁ A liquid drop attains spherical shape due to surface tension as for given volume, sphere has minimum surface area.