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Mass
The mass of a body is the amount of matter in the body.
The S.I. unit of mass is kilogram (kg).
Mass can be measured with the help of spring balance.
Some interested information (not part of IGCSE)
| Planet | Mass of the planet |
| Mercury | 0.33 x 1024 kg |
| Venus | 4.87 x 1024 kg |
| Earth | 5.98 x 1024 kg |
| Mars | 0.65 x 1024 kg |
| Jupiter | 1900 x 1024 kg |
| Saturn | 570 x 1024 kg |
| Uranus | 87 x 1024 kg |
| Neptune | 100 x 1024 kg |
| Pluto | 0.7 x 1024 kg |
| Total mass of all the planets | ~2700 x 1024 kg |
| The mass of the sun | 41.989 x 1030 kg |
All the planets add up to only just over 1/1000th the mass of the sun.
Spring balance
A spring balance can be used to determine the mass of the objects.
The upper end of the spring is hung from a hook and the spring is stetched by the weight of the pan attached to its lower end.
The scale then can be adjusted so that the pointer is aligned with the zero mark.
The balance can be graduated by placing known mass in the pan.
If the spring balance shows 30 N then the mass would be W / g = 30 / 10 = 3 kg, Where g is the acceleration due to gravity.
If this balance is moved to the moon the weight would be less and spring would not stretch so far.
In fact the pointer would indicate a weight of 4.8 N (Because the value of g on the moon is 1.6 m / s2, which is the 1 / 6th of the gravitational acceleration of earth)
So spring balance measures the weight of the object in Newtons.
Remember: Mass of the object remains same every where (either on the moon or the earth)
Weight
Weight is the force of gravity on the object.
It is measured in Newtons (N).
The weight of object depends upon its mass and the gravitational field strength (gravitational acceleration).
Any mass near the surface of earth has weight due to the earth’s gravitational pull.
Weight can be calculated using the equation
Weight = mass (m) X gravotational field strength (g)
w = mg
The value of the gravitational field strength on earth is 9.81 N/kg, through we roound it up to 10 N/kg or 10 m / s2 to make the calculations easier.
Gravitational field is the region arround earth for any body, in which object enters will get the force of atarction towards the center of earth.
If you will stand on the moon, you will feel the gravity of the moon pulling you downward towards the center of the earth.
The gravitational field strengh on the moon is very less as compared to the earth.
On the moon gravitational field strength is 1.6 N / kg or 1.6 m / s2.
Difference between mass and weight
Mass is amount of matter in an object but weight is force of gravity on the object.
Mass is measured in kilograms but weight is measured in newtons as it is a force.
Mass is a scalar quantity but weight is the vector quantity.
Mass can be measured by using level(physical) balance while weight is measured by using spring balance.
Mass remains constant everywhere but weight varies from place to place.
For example if your weight on earth is 500 N so your mass is 50 kg.
If you stand on moon still your mass would be 50 kg, but your weight would be 80N only because g = 1.6 N/kg or 1.6 m / s2 on moon.