Mass, weight and gravity.pptx

The presentation is meant for physics students of high schools or O-Level

1. Mass, weight and gravity Secondary or O-Level physics ~Dr Lalit kishore The Plenum School, HP

2. Mass The amount of matter in an object is called mass Mass is a fundamental physical quantity besides length, time, luminosity, temperature, electric SI unit of mass is kilogram The standard 1 kg mass is being kept at the International Bureau of Standards in Paris which is universally accepted for calibration all the National Bureau of Standards or Standards Institutes in various countries for calibration or marking of their mass measures

3. Gravity The pull of the Earth is called gravity or gravitational force Under free fall, gravity increases the velocity of the dropped object in every successive time interval or gravity as a downward force toward the earth accelerates an object dropped from a height. The acceleration caused by gravity is called the acceleration due to gravity denoted by ‘g’ Galileo found that all bodies take the same time to come to ground when dropped from same which was verified by feather and coin experiment of free fall in a vacuum tube

4. Weight as another name of gravitational force The average value of g is 9.81 metres per second square which is a constant value However, for fair approximation ‘g’ is taken as 10 metres per second square which is a constant value The force caused by gravity on 1 kg mass is approximately 10 N Gravity/gravitational force is also called “weight” Gravity/gravitational force on 1 kg mass = 10 N Or, weight of 1 kg mass = 10 N Or, acceleration due to gravity = 10 N / kg or 10 m per second square

5. Calculating weight The formula for calculating weight In words Weight = Mass X acceleration due gravity Weight = Mass X gravitational force per unit mass In symbols w = mg

6. Comparing mass and weight Mass Weight Mass is quantity of matter in an object– a fundamental physical quantity Scalar Unit = kg Symbol = m Conserved Weight is gravitational force of the earth on an object – a derived physical quantity Vector Unit = N or kgf (1 kgf = 10 N) Symbol = mg Changes from place to place and with distance from the earth

7. Pan balance to compare standard mass with a given mass for measurement The beam of pan balance is in equilibrium when mass of the object and counter mass measures (put on the right pan) are the same Pan balance is lever of first kind In labs the standard mass measures are kept in a weight box Parts: Object pan, object arm, fulcrum, counter mass pan, counter mass arm