Science
Lesson: Mass and Weight
Learning Objectives: Differentiate mass from weight.
: Determine the weight of an object given its mass.
Mass can be measured using a weighing scale (in the market), a platform balance (in a laboratory),
or a bathroom scale (in school). The standard International System of mass is the kilogram (kg).
Smaller are the hectogram, decagram, gram, decigram, centigram, and milligram.
Weight is the measure of the heaviness of an object. It is defined as the force exerted on a body by
the earth’s gravity.
The acceleration due to gravity is the change of the speed affected by gravity on a freely falling
object. It was determined to be 9.8 m/s2.
Weight is mathematically stated as the product of mass and acceleration due to gravity.
𝑾 = 𝒎𝒈
Where W is the weight, m is the mass of the object and g is the acceleration due
to gravity.
The unit of weight is the combination of the unit of mass and the unit of acceleration. A 1 kg mass is
accelerated at 9.8 m/𝑠 2 by gravity, therefore its weight is 9.8 kg-m/𝑠 2 or 9.8 Newton. Newton,
abbreviated as N, is the unit of force in the SI system. Newton is used in honor of the scientists, Sir
Isaac Newton, who formulated the three laws of motion.
Your mass on earth is the same anywhere you go. But your weight will vary slightly as you go from
one place to another that is higher in elevation.
Three system of units
Units of Measure of Mass, Weight, and Acceleration due to Gravity
System of Units
Mass (m)
Weight
MKS
(meter-kilogramsecond)
CGS
(centimeter-gramsecond)
FPS
(foot-poundsecond)
Kilogram (kg)
Newton
Gram (g)
Dyne
Slug
Pound(lb.)
Acceleration due to
Gravity (g)
9.8 meter per
second square
(m/𝑠 2 )
980 centimeter per
second square
(cm/𝑠 2 )
32 feet per second
square (ft./ 𝑠 2 )
Sample Problems:
1. A boy standing on a bathroom scale has a mass of 40 kilograms. If the gravity is 9.8m/𝑠 2 , what is
the weight of the boy?
Given:
Mass = 40 kilograms
acceleration due to gravity (g) = 9.8 m/𝑠 2
Note: 1kg m/𝑠 2 is equal to 1 Newton
Find: Weight
Formula:
W = mg
Weight = mass x acceleration due to gravity
Solution:
W = (40 kilograms) (9.8 m/𝑠 2 )
W = 392 kgm/𝑐 or 392 Newton
Example number 2: Calculate the weight of a man with a mass of 60 kilograms.
Given:
Mass = 60 kilograms
Find: Weight
Formula:
W = mg
Weight = mass x acceleration due to gravity
Solution:
= (60 kilograms) (9.8 m/ 𝑠 2 or Newton)
W
= 588 kgm/𝑠 2 𝑜𝑟 𝑁𝑒𝑤𝑡𝑜𝑛
Remember




Mass is a measure of how much matter something contains.
Weight is a measure of how strongly gravity pulls on something.
The SI unit for mass is kilograms.
The SI unit for gravity is the Newton.