Mass and Weight
In this article we are going to learn about mass and weight, how to measure mass and weight using instruments and differences between mass and weight.
Definition of terms:
Mass: is the amount of matter in an object. The mass of an object is the measure of the amount of matter in it and it is measured in kilograms (kg) using instruments like bath room scale or triple beam balance. The unit of mass is kilogram (kg).
Weight: is the force applied on a body due to gravity. The weight of the body is the force of gravity acting on it. Weight is measured in newtons (N) using an instrument called spring balance. The unit of weight is newton (N).
Differences of mass and weight:
Mass:
It is the same on every planet.
Depents on the amount of matter in an object which keeps it same on each planet.
It is measured in kilograms (kg).
Constant.
Weight:
It is not the same on each planet.
Depents on the value of g (gravitational field strength) which differs on each planet.
It is measured in newtons (N).
Varies with planets.
Calculations of mass and weight:
Mass and weight can be calculated using this equation W = mg .
WHERE:
W is weight.
m is mass.
g is the gravitational field strength.
NOTE: that g varies with planets. The value of g on Earth is approximately 9.8 N/kg or 10 N/kg while on the Moon is 1.6 N/kg.
Given this formula we can find W, m, and g if we have the values of two variables.
Worked example:
Question: A man is driving a car of 4 000 000g taking science students to the science fair. Calculate the weight of this car.
Solution: First step; We should list our known and unkown variables down.
W = ?
m = 4 000 000g
g = 9.8 N/kg
Second step; We should write the formula down to place our variables. But we should convert 4 000 000g to kg so that we can calculate. 1kg = 1 000g so 4 000 000g = 4 000 kg and now we can solve.
Our formula: W = mg
W = mg
W = 4 000 kg x 9.8 N/kg
W = 39 200 N
The weight of the car is 39 200 N.
Assuming that the car is moving on the Moon, the weight will be:
W = mg
W = 4 000 kg x 1.6 N/kg
W = 6 400 N
The weight of the car on the Moon will be 6 400 N.
Therefore, we can conclude that the more gravitational field strength (g) the more weight an object have. Remember mass is constant.