why inertia is another name for mass?

Answer 1

ummm....it's not.
Inertia is the property of an object(aka mass) to remain constant in velocity unless acted upon by an outside force. So in other words, if you push something, it wont stop unless something stops it (like gravity or friction on earth)

Answer 2

Inertia is defined as the reluctance of an object to move. Nothing wants to move because it has inertia.

Inertia is not mass, but inertia is measured as mass. Is that still confusing? Good luck.

Answer 3

It should be emphasised that 'inertia' is a scientific principle, and thus not quantifiable. In common usage, however, people may also use the term "inertia" to refer to an object's "amount of resistance to change in velocity" (which is determined by its mass), and sometimes its momentum, depending on context (e.g. "this object has a lot of inertia"). The term "inertia" is more properly understood as a shorthand for "the principle of inertia as described by Newton in his First Law."

In simple terms we can say that "In an isolated system, a body at rest will remain at rest and a body moving with constant velocity will continue to do so, unless disturbed by an unbalanced force"



Physics and mathematics appear to be less inclined to use the original concept of inertia as "a tendency to maintain momentum" and instead favor the mathematically useful definition of inertia as the measure of a body's resistance to changes in momentum or simply a body's inertial mass.

This was clear in the beginning of the 20th century, when the theory of relativity was not yet created. Mass, m, denoted something like amount of substance or quantity of matter. And at the same time mass was the quantitative measure of inertia of a body.

The mass of a body determines the momentum P of the body at given velocity v; it is a proportionality factor in the formula:

P = mv
The factor m is referred to as inertial mass.

But mass as related to 'inertia' of a body can be defined also by the formula:

F = ma
By this formula, the greater its mass, the less a body accelerates under given force. Masses m defined by the formulae (1) and (2) are equal because the formula (2) is a consequence of the formula (1) if mass does not depend on time and speed. Thus, "mass is the quantitative or numerical measure of body’s inertia, that is of its resistance to being accelerated".

This meaning of a body's inertia therefore is altered from the original meaning as "a tendency to maintain momentum" to a description of the measure of how difficult it is to change the momentum of a body.


Inertial mass
The only difference there appears to be between inertial mass and gravitational mass is the method used to determine them.

Gravitational mass is measured by comparing the force of gravity of an unknown mass to the force of gravity of a known mass. This is typically done with some sort of balance scale. The beauty of this method is that no matter where, or on what planet, you are, the masses will always balance out because the gravitational acceleration on each object will be the same. This does break down near supermassive objects such as black holes and neutron stars due to the high gradient of the gravitational field around such objects.

Inertial mass is found by applying a known force to an unknown mass, measuring the acceleration, and applying Newton's Second Law, m = F/a. This gives an accurate value for mass, limited only by the accuracy of the measurements. When astronauts need to be weighed in outer space, they actually find their inertial mass in a special chair.

The interesting thing is that, physically, no difference has been found between gravitational and inertial mass. Many experiments have been performed to check the values and the experiments always agree to within the margin of error for the experiment. Einstein used the fact that gravitational and inertial mass were equal to begin his Theory of General Relativity in which he postulated that gravitational mass was the same as inertial mass, and that the acceleration of gravity is a result of a 'valley' or slope in the space-time continuum that masses 'fell down' much as pennies spiral around a hole in the common donation toy at a chain store.

Since Einstein used inertial mass to describe Special Relativity, inertial mass is closely related to relativistic mass and is therefore different from rest mass.





Inertia=not mass

Answer 4

It isn't. Inertia is a principle: an object at rest will stay at rest until acted upon by an equal or greater force; an object in motion will stay in motion until acted upon by an equal or greater force.

Answer 5

Inertia is not mass.

Answer 6

It isn't.

The measure of inertia is momentum.

Change of momentum implies force - force is given by the rate of change of momentum.