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Difference
Between Mass and Weight
Students of
physics often confuse mass and weight of an object and many also feel that
there is no difference between the two, while the fact is that there is a
lot of difference between the two.
Mass is the
amount of matter present in a body and is an intrinsic property of the
body. Mass of an object remains the same always at any place.
Weight on the
other hand is the force which a given mass feels due to the gravity at its
place. Weight is measured in units of Force like Newton (which is the SI
unit of Force).
If your mass
is 60 kgs then your weight is approximately 60 x 10 = 600 Newtons. This is
because
Force = mass
x acceleration (From
Newton's second Law)
Thus, weight
= mass x acceleration due to gravity
If you go to
moon your mass remains same, i.e 60 kgs, but your weight becomes less by
1/6 amount, since moon's gravity is 1/6 that of earth.
Mass of a body
is measured by balancing it equally with another known amount of mass. You
keep known amount of masses like blocks of 1 kg, 2 kg etc on one side till
both the sides balance and then add up the numbers on the known side of
mass and thus calculate the unknown mass. This works because, when the
masses are equal on both the sides of the balance the effect of gravity
cancels out for both (i.e weight cancels out) and hence we can calculate
the mass on one side of the balance if we know the mass on the other side
of the balance.
Weight is
measured using a scale which effectively measures the pull on the mass
exerted by the gravity of the earth.
Table 1:
Differences between Mass and Weight
| |
Mass |
Weight |
| 1. |
Is always a
constant at any place and time |
Depends on
gravity at the place |
| 2. |
Is measured
in kilograms in SI unit |
Is measured
in Newtons (not in kilograms as one might think) |
| 3. |
Is measured
using balance |
Is measured
using scales |
| 4. |
Can never be
zero |
Can also be
zero |
| 5. |
Is an
intrinsic property of a body and is independent of any external
factor. |
Depends on
1. Mass of the object which is attracting it
2. Force with which it is being attracted (which in turn depends
on the distance between the two) |
If an object
is in freefall towards the attractor (like earth), even then it has
weight, but it experiences weightlessness (like an astronaut in a
spaceship around the earth) since it is obeying the force. Weight can be
felt only when the body in question tends to oppose the force of gravity
(like u and me sitting on the surface of the earth:-)
Remember that
even though we are at rest due to the friction between our self and earth's
surface, our acceleration is not zero, it is still 9.8 m/s2 as
the earth is constantly pulling us down towards its center. But we are
resisting that pull and feel the force as weight.
-by Gurudev
MADE IN
INDIA
gurudevp@vsnl.net
On 2 September 2002
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