its
resistance to acceleration.

### LEARNING OBJECTIVE

·
Explain the difference between mass
and weight

### KEY POINTS

·
The kilogram is the only SI unit
directly defined by the artifact itself.

·
One kilogram is defined as the mass
of the International Prototype Kilogram (IPK), a platinum-iridium alloy
cylinder.

·
One kilogram is almost exactly equal
to the mass of one liter of water.

### TERMS

the rate at which the velocity of a body changes with time

·
inertia

the tendency of an object to resist any change in its motion

### FULL TEXT

Mass

Mass,
specifically inertial mass, is a quantitative measure of an object's resistance to acceleration. It is an intrinsic property of an object and
does not change because of the environment. The SI unit of mass is the kilogram
(kg).

The
kilogram is defined as being equal to the mass of the International Prototype
Kilogram (IPK), which is almost exactly equal to the mass of one liter of
water. It is also the only SI unit that is directly defined by an artifact,
rather than a fundamental physical property that can be reproduced in different
laboratories. Four of the seven base units in the SI system are defined relative to the kilogram, so the stability of this
measurement is crucial for accurate and consistent measurements.

In
2005, the International Committee for Weights and Measures (CIPM) recommended
that the kilogram be redefined in terms of a fundamental constant of nature,
due to evidence that the International Prototype Kilogram will vary in mass
over time . At its 2011 meeting, the General Conference on Weights and Measures
(CGPM) agreed that the kilogram should be redefined in terms of the Planck constant. The conference deferred a final decision
until its next meeting in 2014.

Mass and Weight

In
everyday usage, the mass of an object in kilograms is often referred to as its
weight. This value, though given in kilograms, is actually the non-SI unit of
measure known as the kilogram-force. In scientific terms, 'weight' refers to the gravitational force acting on a given body. This
measurement changes depending on the gravitational pull of the opposing body.
For example, a person's weight on the Earth is different than a person's weight
on the moon because of the differences in the gravitational pull of each body.
In contrast, the mass of an object is an intrinsic property and
remains the same regardless of gravitational fields. Accordingly, astronauts in
microgravity must exert 10 times more force to accelerate a 10-kg object at the
same rate as a 1-kg object, even though the differences in weight are
imperceptible.

*Source,credits and courtesy: boundless.com*

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