A Taste of what you’ll Learn
Basic definition of Mass
Basic definition of weight
Relationship between mass and weight
Differences between mass and weight
A mass of a body is the quantity of matter contained in the body. It is scalar quantity I.e. it has magnitude but no direction. The unit of mass is kilogramme (kg).
This is a measure of the force of gravity of the earth on a body. It is a gravitational pull of the earth on any body towards its centre. It is a vector quantity I.e. it has magnitude as well as direction. The unit of weight is Newton (N).
Relationship between mass and Weight
Weight of a body = Force
Force = mass of body x acceleration due to gravity
I.e. W = F = mg
m = W/g
Find the weight of a ball if the mass of the ball is 10kg and the acceleration to gravity is 10m/s2.
W = mg
W = 10 kg x 10 m/s2
W = 100N
Difference between mass and Weight
1) Mass is the quantity of matter contained in a body While weight is the measurement of the force of gravity on a body.
2) Mass is a scalar quantity while weight is a vector quantity.
3) The S.I. unit of mass is kilogramme while the S.I. unit of weight is Newton.
4) Mass of the body is constant throughout the universe, while weight varies from place to place in the universe.
5) The instruments used to measure mass can be beam balance, lever balance or chemical balance, while the instrument used to measure weight is spring balance.
- Read on the Equations of motion
Mass and weight - on moon
An astronaut on earth weighing 980N and mass of 100kg (acceleration due to gravity on earth is 9.8m/s^2).
Weight on Earth: 100kg x 9.8m/s2 = 980N.
The same astronaut on the moon would weigh 162.2N and have a constant mass of 100kg (acceleration due to gravity is 1.622m/s^2)
Weight on Moon: 100kg x 1.622 m/s2 = 162.2N.
1) The mass of a rock on the Earth is 2.0 kg. What is the mass of the rock on the Moon?
2) Why is weight not equal everywhere?
A) Because of altitude.
B) Because of the varying mass other planets when compared with earth.
C) Because of force of gravity
D) All of the above
E) None of the above
3) An astronaut of mass 40 kg jumped out of the rocket after it had landed on Jupiter. The astronaut took 0.40 s to drop for 2.0 m. What was the weight of the astronaut on Jupiter?
4) A student's weight on Earth is 100 pounds. If this student went to the Moon,what would he weigh?
C) the same
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