What Is Inertia and How Does It Influence Motion?

• gunblaze
In summary, inertia is a fundamental concept in physics that refers to the resistance of an object to changes in its state of motion. It is neither a vector nor a scalar, but a property of matter that is quantified by its inertial mass. Inertia is not a force in the social sense, but can be overcome with money or brute force. In programming, inertia is represented as a vector, but in physics it is more accurately described as a scalar. Its relationship to mass is important in understanding the effects of gravity.
gunblaze

What really is INERTIA?

Is it a force.?
A vector or a scalar?
What can be known only by the defination?

Does it really have anything to do with physics?

Inertia is probably the most fundamental concept in physics: it is resistance to acceleration. For the purpose of the first learning of Newton's laws (f=ma), mass and inertia are the same, but don't take that to mean that the term "inertia" is superfluous. It isn't. There are several types of inertia.

Last edited:
INERTIA is a phenomenon (it is neither a vector nor a scalar).

Russ:
The high school teacher in me comes out; Inertia is the resistance to change in motion. I know you know that.

Chi Meson said:
Russ:
The high school teacher in me comes out; Inertia is the resistance to change in motion. I know you know that.
Oh, is that what the "a" stands for in that equation? Yeah, I knew that - fixed now.

edit: perhaps I was thinking in terms of politics...? http://dictionary.reference.com/search?q=inertia

Last edited:
gunblaze said:

What really is INERTIA?

Is it a force.?
A vector or a scalar?
What can be known only by the defination?

Does it really have anything to do with physics?

Don't know if this is what you're asking, but for me this was once like the question asked in another thread, "What are Field Lines?" If your question is Why is inertia? or, Why does matter resist changes in motion?, then I believe the answer, to date, is, "We don't know." - which is why clive referred to it (correctly) as a phenonemon.

Yeah, just to throw in my two cents towards the "phenomenon" camp, I've heard it described this way:

Inertia is a property of matter.

Mass (inertial mass) on the other hand, is a quantity, in fact it quantifies inertia in that it provides a means of physically measuring the effect i.e. we apply a force F to a body, we measure a, we determine what m is, the larger it is, the more difficult a time we had of accelerating the body. What do you guys think of that?

gunblaze said:

What really is INERTIA?
in·er·tia [i núrsh?] noun
1.apathy: inability or unwillingness to move or act
2.resistance to change: the property of a body by which it remains at rest or continues moving in a straight line unless acted upon by a directional force

[Early 18th century. From Latin, “lack of skill, inactivity,” formed from iners (see inert

The inability or unwillingness of a person to move or act is only indirectly related to that person's mass.

For some people, inertia can be overcome with money. For others, one has to use brute force, in which case Newton's second law is a reasonable approximation.
A vector or a scalar?
A scalar.
Is it a force.?
No. Not even a force in the social sense.

AM

cepheid said:
Yeah, just to throw in my two cents towards the "phenomenon" camp, I've heard it described this way:

Inertia is a property of matter.

Mass (inertial mass) on the other hand, is a quantity, in fact it quantifies inertia in that it provides a means of physically measuring the effect i.e. we apply a force F to a body, we measure a, we determine what m is, the larger it is, the more difficult a time we had of accelerating the body. What do you guys think of that?

You raise a question that's been on my mind for some time.

It's interesting to me that, given the direct correlation between mass and its inherent inertia (simplistically speaking), we actually use inertia to quantify the mass of a given body. If that property did not exist (hypothetically, of course), could we quantify mass by any other means?

What I'm really getting at: Is the correlation between mass and inertia a known absolute? Is it possible that there exists matter that is more (or less) massive than its inertial properties suggest?

I was saying mass quantifies inertia, not the other way around. If it were not for this property, the quantity known not surprisingly as "inertial mass" would not have any meaning. It is literally defined by the m in Newton's 2nd law. So mass IS a measure of an object's resistance to a change in state of motion, ie of its inertia. That's how I understand it.

Gravitational mass as I understand it is quantity that crops up as another proportionality constant. One that relates the gravitational field strength to the force (weight) experienced by a body in that field. Also symbolized as "m" and called "mass". The fact that inertial mass and gravitational mass are equivalent is very important, as I recall.

I don't think "mass" has meaning outside these contexts (in classical physics). Corrections to these notions of mine are most welcome.

Last edited:
Andrew Mason said:
in·er·tia [i núrsh?] noun
1.apathy: inability or unwillingness to move or act
2.resistance to change: the property of a body by which it remains at rest or continues moving in a straight line unless acted upon by a directional force

[Early 18th century. From Latin, “lack of skill, inactivity,” formed from iners (see inert

The inability or unwillingness of a person to move or act is only indirectly related to that person's mass.

For some people, inertia can be overcome with money. For others, one has to use brute force, in which case Newton's second law is a reasonable approximation.
A scalar.
No. Not even a force in the social sense.

AM

Hey all,

I'm a programmer and don't know too much about physics.

I'm currently working one a game with realistic physics and I'm use the physics library http://www.bulletphysics.com/" . It simulates rigid bodies.

Andrew Mason says Inertia is a scalar but in Bullet it is represented as a vector. So I'm still very confused as to what Inertia is. I understand the phenomenon idea (mentioned above) but I'm having trouble understanding how to computers to a vector or a scalar.
I learned at school (along time ago) that f(force)=m(mass)a(acceleration) but this would be a rule there would be used in Bullet and not a number(vector or scalar).

Any idea on this would be nice. :)

Johnny

Last edited by a moderator:
Inertia is the property of bodies which always oppose the change of state.

If a body is in the state of rest because of inertia property it would like to continue its state of rest.

To change this state we need to apply force.

This gives foundation for Newton's first law.

maxcode said:
[...]
I'm currently working one a game with realistic physics and I'm use the physics library http://www.bulletphysics.com/" . It simulates rigid bodies.

Andrew Mason says Inertia is a scalar but in Bullet it is represented as a vector. [...]
I learned at school (along time ago) that f(force)=m(mass)a(acceleration) but this would be a rule there would be used in Bullet and not a number(vector or scalar).

Any idea on this would be nice. :)
[...]
From a quick look through their forum it seems what you are looking for is the "http://en.wikipedia.org/wiki/Moment_of_inertia" "
It is a 2d tensor (matrix) though and not a vector (1d tensor). If you want you can see it as an extension of the concept of mass for rotations.

Last edited by a moderator:
I pretty much agree with the post of d_vsuresh...

Basically, in my experience, inertia is a colloquial or intuitive sort of term. You never usually calculate "inertia" as a fundamental quantity, unlike mass or acceleration. Sometimes we have quantities known as "inertial forces", but that's basically a matter of nomenclature.

Essentially inertia is just the propensity of a body to continue in the same state of motion unless acted on by outside forces. If acted on by outside forces, the inertia of the body tends to resist those forces.

What is Newton's first law of Inertia?

Newton's first law of Inertia states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

What is the relationship between mass and inertia?

The greater the mass of an object, the greater its inertia. This means that the object will be more resistant to changes in its state of motion.

How does Newton's first law apply to everyday life?

Newton's first law applies to everyday life in many ways. For example, when you push a shopping cart, it will continue to move unless an external force (such as friction) acts upon it. Similarly, when you slam on the brakes in a car, your body will continue to move forward due to inertia.

What is the difference between inertia and momentum?

Inertia is the resistance an object has to changes in its state of motion, while momentum is the quantity of motion an object has. Inertia is dependent on mass, while momentum is dependent on both mass and velocity.

How does Newton's first law relate to the concept of equilibrium?

Newton's first law can be thought of as a definition of equilibrium. An object in equilibrium has no net force acting on it, which means it will either remain at rest or continue its motion at a constant velocity. This is in line with Newton's first law, as an object will remain in its state of motion unless acted upon by an external force.

• Thermodynamics
Replies
16
Views
950
• Thermodynamics
Replies
20
Views
2K
• Thermodynamics
Replies
2
Views
1K
• Thermodynamics
Replies
17
Views
1K
• Thermodynamics
Replies
9
Views
1K
• Thermodynamics
Replies
4
Views
1K
• Thermodynamics
Replies
4
Views
956
• Thermodynamics
Replies
7
Views
3K
• Thermodynamics
Replies
2
Views
766
• Thermodynamics
Replies
4
Views
1K