Mass, Force and Weight
The mass of a body is a measure of the quantity of matter in the body. The mass of a specified collection of matter is not modified by such things like;
(a) Change of position
(b) Deformation of figure
(c) Alter of temperature
(d) Chemical reactions that the matter undergoes.
Such facts state the content of the law of conservation of mass. Some of the procedures that do modify the mass of a body are as follows:
(a) Nuclear reaction
(b) Acceleration to velocities as comparable to the speed of light.
Force is imagined as the pull and push which tend to make objects move. It has both direction and magnitude, and is treated mathematically as a vector. The vector sum of all forces acting on a body which is not accelerating should be zero.
The unit of force is stated by means of Newton’s second law of motion that forms the foundation of the science of dynamics and is also a significant portion of thermodynamics:
“One Newton (N) is the magnitude of the force that acting on a body of one kilogram mass, causes it to accelerate at the rate of 1 m /s2 in the direction of the force”.
The weight of a body on earth is associated to the gravitational force applied by the attraction of the earth. While the mass of a body is steady, the weight of the body differs (i.e., by a few tenths of a percent) with location on the earth’s surface. It reduces considerably in outer space, soon becoming negligible as compared with the gravitational attraction applied by other heavenly bodies.
Example:
A spring balance that is designed to measure weight is to be used for establishing the mass of a sample of moon rocks on the moon’s surface. The spring was initially calibrated for the earth’s gravitational acceleration of 9.8 m/s2. Calculate the mass of the sample. What would be the reading on a beam balance scale?
Solution:
As the spring was calibrated for the earth’s gravitational field, the force equivalent to a reading of 1 kg on the spring balance is as follows:
1 kg × 9.81 m/s2 = 9.81 N
The force equivalent to a reading of 4.5 kg is :
4.5 × 9.81 = 44.15 N
As the gravitational acceleration on the moon is 1.8 m/s2,
Hence, Mass of sample = 44.15/ 1.8 kg = 24.53
As beam balance measures mass, it will point out a reading of 24.53 kg.