Inertia Definition and 1000 Threads

Inertia is the resistance of any physical object to any change in its velocity. This includes changes to the object's speed, or direction of motion.
An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces act upon them.
Inertia comes from the Latin word, iners, meaning idle, sluggish. Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems. Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia Mathematica, which states:

The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line.
In common usage, the term "inertia" may refer to an object's "amount of resistance to change in velocity" or for simpler terms, "resistance to a change in motion" (which is quantified by its mass), or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his first law of motion: an object not subject to any net external force moves at a constant velocity. Thus, an object will continue moving at its current velocity until some force causes its speed or direction to change.
On the surface of the Earth, inertia is often masked by gravity and the effects of friction and air resistance, both of which tend to decrease the speed of moving objects (commonly to the point of rest). This misled the philosopher Aristotle to believe that objects would move only as long as force was applied to them.The principle of inertia is one of the fundamental principles in classical physics that are still used today to describe the motion of objects and how they are affected by the applied forces on them.

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  1. I_Try_Math

    Analyzing torque of an automobile engine

    My strategy for this problem is to use the equation, ## \sum \tau = I\alpha ## to find ## \alpha ##. ## I_{total} = I_{shaft} + I_{axle} + 2(I_{wheel}) ## ## I_{wheel} = I_{disk (hub)} + I_{ring (wall)} + I_{ring (treads)} ## Is this the correct way to calculate the moment of inertia?
  2. I_Try_Math

    Finding the angular velocity of a pendulum

    My answer disagrees with the textbook and I have a feeling it may be due to how I calculated the moment of inertia. Is there anything obviously wrong with my calculation? Any help is appreciated. ## I_{sphere} = \frac{2}{5}MR^2 + Md^2 ## ## I_{rod} = \frac{1}{3}ML^2 + Md^2 ## ## I_{sphere} =...
  3. Math Amateur

    I A. P. French "Matter and Radiation: The Inertia of Energy"

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  4. davidortenn79

    B Why is it impossible to go faster than the speed of light?

    Ok, I took like a class in physics in college. It was a class to learn physics for majors that we really didn't care. I remember him saying, if you remember anything from this class, remember inertia. That's about all I remember from the class... lol. But, I don't understand why it's...
  5. potatoboy

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  6. dcmf

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  7. F

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  8. G

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  9. Vic43

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  10. P

    I How Is Power Calculated in a Rotating System with Variable Speed?

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  11. KataruZ98

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  12. G

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  13. G

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  14. A

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  15. J

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  16. M

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  17. G

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  18. G

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  20. P

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  21. L

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  22. L

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  23. L

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  24. H

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  25. N

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  27. S

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  28. A

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  29. Math Amateur

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  30. S

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  31. AF Fardin

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  32. L

    Moment of inertia of a uniform square plate

    I placed my Oxy coordinate system at the center of the square, the ##x##-axis pointing rightwards and the ##y##-axis pointing upwards. I divided the square into thin vertical strips, each of height ##h=2(\frac{L}{\sqrt{2}}-x)##, base ##dx## and mass ##dm=\sigma h...
  33. S

    I Explaining how the Higgs fields gives particles mass

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  34. C

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  35. V

    Moment of inertia of a disk about an axis not passing through its CoM

    I have come up with two different approaches, but I'm not sure which one is correct since they give different answers. We use the following equation to get the total moment of inertia. ##I_o## = moment of inertia of disk about O axis + moment of inertia of road about O axis Approach 1...
  36. GopherTv

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    What kind of experiment can I design to determine the actual value of the moment of inertia. What should I instruct the sphero to do and what data should I collect?
  37. jaketodd

    B Are zero-point energy and inertia incompatible?

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  38. V

    What is the "r" in the moment of inertia?

    We solved this problem in class as follows: Net torque about the center of the pulley taking counterclockwise rotation to be positive = m1gR - m2gR = I_tot α, where I_tot is the moment of inertia of the full system. My professor said that I_tot = I + m1R^2 + m2R^2, where m1R^2 is the moment...
  39. George Keeling

    I Time derivative of the moment of inertia tensor

    I am completely stuck on problem 2.45 of Blennow's book Mathematical Models for Physics and Engineering. @Orodruin It says "We just stated that the moment of inertia tensor ##I_{ij}## satisfies the relation$${\dot{I}}_{ij}\omega_j=\varepsilon_{ijk}\omega_jI_{kl}\omega_l$$Show that this relation...
  40. A

    Find the inertia of a sphere radius R with rotating axis through the center

    $$I = \int{r^2dm}$$ $$dm = \sigma dV$$ $$dV = 4\pi r^2dr$$ $$\sigma = \frac{M}{\frac{4}{3}\pi*R^3}$$ $$I = \sigma 4 \pi \int_0^R{r^4 dr} = \frac{3*MR^2}{5},$$ which is not the correct moment of inertia of a sphere
  41. M

    What's wrong with my solution? -- Area moment of inertia

    I used the parallel axis theorem to solve the question but my answer is still wrong. Any ideas where I slipped? I can't seem to figure out the problem?
  42. Carlos Torres

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  43. DrunkElk1601

    I Energy Transfer Between Inertia Wheels

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  44. curiousPep

    I Resolve moment of inertia at an angle

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  45. E

    Calculate Deflection for Aluminium Tube Beam - Inertia, Mass & δ

    Hi There, I am wanting to calculate the amount of deflection (δ) from a simply supported Beam. My Beam is an Aluminium Tube ø30mm with a 3mm Wall Thickness. Force (F) - 500N Length (L) - 610mm Youngs Modulus (E) - 68 Gpa Moment of Inertia (I) - ? δ = F L³ ∕ 48 E I Q1: Is this the correct...
  46. SpaceThoughts

    I How to calculate gyroscopic inertia this setup?

    This text refers to the photo below. The wheel in the middle can rotate vertically without friction. The construction around it can rotate the wheel horizontally as well, also without friction. When the blue weight is falling while the wheel is not rotating, I can calculate the kinetic energi...
  47. A

    Moment of Inertia of a 4 rod system

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  48. G

    Inertia units for a synchronous machine

    Hello everyone, I'm sorry if this is not the right sub-forum to post this, but this doubt has been haunting me for a while. I've got some rotatory machine -let's say, generic synchronous machine-. Turns out there are typical values for [kg m^2] (inertia) in the 2-10 range; the software I'm...
  49. Tapias5000

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    My solution is now I am asked for the same result but in this form but I don't know where to start.
  50. S

    B What would happen if there were no inertia?

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