What exactly is inertia?
Can inertia change?
Inertia is a property of matter. It is the resistance of matter to acceleration, or a change in velocity. It is dependent upon mass, and independent of everything else, and does not change.
Slight Hijack; is inertia and momentum the same thing?
Not exactly, but they are related. Momentum is a property of moving matter (matter at rest has zero momentum). Inertia applies to all matter, moving or not.
I think momemntum applies to stationary objects too and since we are in Newtonian (Inertial) Mechanics rest and motion are relative anyways.
But inertia and momentum of a body are not the same thing. Inertia of a body implies the resistance to change its momentum when an external force is applied.
Now two bodies having the same momentum can have different inertia. For example a 1kg body traveling at 1 m/s and a 0.5kg body traveling at 2 m/s have the same momentum, but the 1kg body has a larger inertia.
If a person could position themselves so that they were stationery in relation to the Milky Way and could illuminate a single point on the Earths equator and see it’s motion within the galaxy, what would it look like, spirals on spirals on spirals of ever increasing dimensions?
QED
It is dependent upon mass, and independent of everything else, and does not change.
Doesn’t relativity dictate that inertia DOES change?
Yes it does. Q.E.D.'s statement is fine as far as it goes. SR tells us that mass changes. Q.E.D. said that inertia was dependant on mass. So it follows that inertia changes as mass changes.
No it doesn’t. Relativity does tell us that the equation p = mv is not correct. One possible resolution is to say that mass is dependent on velocity, but it makes much more sense to put the fudge factor on velocity, rather than on mass. So p = mu, where u = [symbol]g[/symbol]v.
Inertia does, indeed, depend on mass (one may even say that inertia is mass), but inertia does not depend on speed.
Well, in a way, I suppose it does “apply”, but at the same time it’s irrelevent for stationary objects. The momentum of an object = the mass of the object x it’s velocity (p=mv). That means that in order for an object to have momentum it must be moving (in the sytem of reference). The point about being in a Newtonian system is valid, but since we have to have some point of reference to be able to apply Newtonian physics, an object is typically said to have momentum if it is moving relative to a chosen (i.e. fixed) point of reference. So, sure, in the grand scheme of the universe, everything has momentum, but that’s a bit much to deal with if you’re just worried about the marbles on the floor in front of you.
Of course, this doesn’t tell us exactly what inertia is.
And we really don’t know. Why is matter resistant to changes in direction and acceleration?
Is everything (and I mean everything) holding everything in place (with regard to uniform motion) and then resists when you try to change it? Is that a sign of faster than light communication? Why isn’t inertia listed as a fundamental force like gravity or electromagnetism? Are there Bavarian economic gnomes or 23rd level illuminati suppressing the real answers?
Peace.
And what’s this orange stuff under my fingernail?
…And how does inertia fit in with the ‘fundamental’ forces? I figure we can rule out the strong and weak nuclear… is it electromagnetic or gravitational in nature? There is nothing else, right?
Inertia isn’t a force. It’s the property of matter that requires a force to cause an object to change velocity. It is directly proportional to mass; in fact, you could conceivably assign a value to it in the same units, e.g., a one-kilogram object could be said to have one kilogram of inertia. I don’t think this is actually done this way, but I could be mistaken.
Moriah, I think that inertia is just another way of showing conservation of energy. If you exert a force to start an object moving, that force cannot just go away. The “resistance” is just the energy previously exerted on the object being countered by other energy.
Chronos – QED
Here are but a few samples I found that state inertia DOES change according to Relativity.
[quote]
But what do we mean by mass ? In Classical Physics we can think of it in two respects:
- the mass of a body is something related to its quantity of matter , i.e. something connected to the number of atoms (as well as the mass of each atom…)
- at the same time the mass is also a measure of the body’s inertia, i.e. its reluctance to having its velocity changed.
In Newtonian Physics these two pictures are interchangeable, but Einstein broke this correspondance : in Relativity, the inertia of an object is not a constant quantity, characteristic of each object, but it is a function of velocity: m=mo / sqrt/1-v^2/c^2
http://galileo.phys.virginia.edu/classes/102.spring99/lec4/lec4.html
This page utilises mass-energy equivalence to show that the mass energy content (or ‘Inertia’) of a body increases with speed, approaching infinity as velocities approach that of electromagnetic radiation in vacuo.This interesting and important result may be deduced from a handful of fundamental principles and a simple integration. Albert Einstein addressed this question in his 1905 paper ‘Is the inertia of a body a measure of its mass/energy content?’
http://www.egglescliffe.org.uk/physics/relativity/relmass/relmass.html
Actually, here’s the way it should be said: energy and mass are related. If you set up a “black box” (box you can’t see into) containing some atoms, the total mass of the box and its contents will be equal to the sum of the mass of the box and mass of the individual atoms in the box. If you heat the box to a high temperature (so the atoms are moving around at high speed in the box, and thus have high energy), then the total mass of the box and its contents will be larger than if the temperature of the box is lower. Why? Because, the higher energy atoms contribute more mass to the total mass than before the box was heated. So, if you try to push on the box, you will discover that its inertia will be larger(it won’t accelerate as quickly).
At low speeds I apply 1 newton of force to 1kg of matter and acclerate at 1m/s.
At high speeds however, that 1 newton of force accelerates that 1kg of matter only .5m/s. So, the INERTIA has changed.