Understanding Inertia: A Guide to its Uses and Importance in Physics

In summary, the concept of inertia is still used in both inertial and non-inertial frames, but it is not considered a force and may be referred to as a fictitious force in certain situations. It is useful in simplifying calculations, but usage of it has been debated among physicists.
  • #1
bobie
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The force of inertia is the property common to all bodies that remain in their state, either at rest or in motion, unless some external cause is introduced to make them alter this state.Is the concept of inertia still used? When is it useful as a fictitious force?

Can you list a few situations in which, if we didn't use this tool we might be in difficulty?
 
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  • #2
  • #4
I would disagree with the previous responses and say that it is NEVER useful as a force. Consider these ideas, please:

1. Newton's 2nd law says Sum F = M * A
This means that all of the real forces appear on the left side (or in the first term if you want to set it all to zero). The M * A is not a force, and therefore should not appear in the force sum.

2. There will be some who will say, "well, it looks just like a force when we look at the 2nd law," and that is true. But the 3rd law says that for every action (force) there is an equal and opposite reaction (force) somewhere in the universe. There simply is no reaction to an "M*A" force, so it must not be a force.

Simon noted above that it is useful "anytime it simplifies the calculation." That is hard to argue with except to ask, "how does it simplify the calculation?" The usual effect to cause the user to pay less than full attention to the expression of the acceleration (usually assuming an unduly simple form), so that it leads to an error.

I strongly suggest, leave D'Alembert in his grave and stick with Newton (or Lagange).
 
  • #5
Useful or not it is sometimes still used - yes, imagine my shock.
We get a lot of questions here about accelerated reference frames where the calculations are best done in those frames.
... but I prefer not to use the phrase "force of inertia" to help people with them as it's too confusing.
 
  • #6
Dr.D said:
2. There will be some who will say, "well, it looks just like a force when we look at the 2nd law," and that is true. But the 3rd law says that for every action (force) there is an equal and opposite reaction (force) somewhere in the universe. There simply is no reaction to an "M*A" force, so it must not be a force.

Well, this is only because such an inertial 'force' does not act upon a body from any external body (except, perhaps a la Newton, from absolute space). I'm not sure the 3rd law is then applicable to it, although this obviously depends heavily on the particular formulation of this law. I'd prefer something like [itex]F_{AB} = - F_{BA} [/itex] rather than the colloquial equal and opposite reaction...
 

What is inertia?

Inertia is a property of matter that describes an object's tendency to resist changes in its state of motion. This means that an object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force.

What are some real-life examples of inertia?

Some common examples of inertia include a book sliding off a table when the tablecloth is pulled out from under it, a car stopping suddenly and causing the passengers to lurch forward, and a person feeling a force pushing them to the side when a car turns.

How is inertia used in physics?

Inertia is a fundamental concept in physics and is used to explain the behavior of objects in motion. It is a key component of Newton's first law of motion, which states that an object will remain in its state of motion unless acted upon by an external force.

Why is understanding inertia important in physics?

Understanding inertia is crucial in physics because it helps us to predict the behavior of objects in motion. It allows us to explain why objects come to a stop, why they change direction, and why they maintain a constant velocity.

How can inertia be manipulated or controlled?

Inertia can be manipulated or controlled by applying external forces to an object. For example, if you want to change the direction of a moving object, you can apply a force in the opposite direction. Additionally, by changing an object's mass or shape, you can affect its inertia and how it responds to external forces.

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