What is Inertia: Definition and 1000 Discussions

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.

View More On Wikipedia.org
Recent contents Top users
  1. VVS2000

    Moment of inertia (experiment)

    So in the above image, I intend to find the moment of inertia of that black rotating object which rotates due to torque which is provided by placing mass on the pulley. But the thing is that this rotating object is kind of like a ball bearing kind of system and even for a small torque it starts...
  2. Eggue

    Moment of inertia of a rod bent into a square

    I tried to find the moment of inertia of 2 rods connected at the corners by adding up their moments of inertia: \frac{1}{3}(\frac{M}{4})a^2 + \frac{1}{3}(\frac{M}{4})a^2 = \frac{1}{6}Ma^2 I then tried to solve for the moment of inertia at the center of mass of the 2 rods using the parallel...
  3. DarkMattrHole

    I Is the inertia of a massive object the result of gravity wave generation?

    Hi all. I just watched a great video on gravity wave 'telescopes'. So i have been wondering if any of my intuitive hunches are right about gravity waves. Accelerated masses generate gravity waves that dissipate energy.. So let's say i turn my rocket ship engine on while sitting in deep...
  4. Andrea Vironda

    I Polar moment of inertia

    Hi, A well-known part of the formula for calculating the deflection stress is ##I_z=\int \int r^2 dA## Usually a moment of inertia is something related to how difficult is to move an object. In this case is understandable but i don't understand the meaning of the double integral. Using ##r^4##...
  5. xWaldorf

    Unraveling the Mystery of Mass and Acceleration

    So, this may be a really stupid question, and I strongly feel as though I'm missing something here. How can it be that objects of different masses have the exact same acceleration when mass is in fact resistance to acceleration? And then, if in (a vaccum) I throw upwards M and m ( a bigger and a...
  6. C

    Why Do Different Objects Share Similar Moments of Inertia?

    Hello, I am a computer science major and Ex-Biology grad student, my knowledge in physics is humble, but I got a little curious when my professor derived the expressions of moment of inertia for different objects. The moment of Inertia of a thin disk is 1/2MR2, but it is the same as the moment...
  7. V

    Determining Inertia of a block

    Since the problem gave me the kinetic energy and inertia of the iron block, I could plug it into the equation K = 1/2 mv^2 to get the final velocity, I got sqrt(30) for the block's final velocity. From there, I don't really know where to go, I could plug it into the equation above, but ΔE int is...
  8. V

    Moment of inertia, conservation of angular momentum and energy

    When I solved the problem using the conservation of angular momentum, I have got the correct result (ω = 0.006 rad/s). However, when I tried to find the answer using the conservation of energy the result was incorrect and I do not understand why.
  9. Like Tony Stark

    Determine tensor of inertia of a rod

    I have to find the inertia tensor of these rods and I don't have the concept that clear... I mean, I know the formulas like: ##I_{xx}=\int y^2 + z^2 dm## ##I_{xy}=\int xy dm## But I don't know what ##x, y, z, dm## stand for. In other words, I don't know what I should replace in the formula...
  10. B

    Instantaneous moment of inertia of an object

    Can someone guide me on how to approach this question? I tried to draw a quick diagram of what I think is happening here Does the question imply that this object is undergoing horizontal circular motion in the shape of a conical pendulum? Thanks for any help!
  11. B

    Rotational motion and finding the moment of inertia

    Here is the problem that I am finding difficult to answer I had tried using conservation of energy to do this question Where I know that the gravitational potential energy at the top of the slope equals to the sum of both the linear and rotational kinetic energy at the bottom of the slope...
  12. L

    Calculate the moment of inertia of this body

    I use the moment of inertia I = 1/12ml2 for an axis perpendicular and passing through the center of mass of a rod. In a cube built out of 12 rods I have 8 rods at a perpendicular distance l/2 from the axis through the midpoint of a cube. These 8 rods contribute the moment of inertia I1 =...
  13. H

    Engineering How to find the first area moment of inertia (Q) for an I-beam with flanges

  14. A

    Harmonic motion of four meter sticks

    inertia of center = [(1/12) m*L^2 + m(L/2)^2]*4 inertia of center = (4m*L^2)/ 3 inertia around pin = (4m*L^2)/ 3 + 4m(L/ 2^(1/2) )^2 inertia around pin = (10m*L^2)/ 3 inertia around pin = (10*0.1*1^2)/ 3 = 0.33 kg*m^2 d= 1/2^(1/2) = 0.707m (m*g*d/inertia)^1/2 = 2pi/period...
  15. Isabel1747

    Rotational Inertia and Net Torque with Friction

    I converted the amount of rotations completed in 5 seconds into radians. 23.4 rot * 2pi = 147 rad I found the angular acceleration of the object in the first 5 seconds it was speeding up. Wf = Wi + at a = 5.881 rad/s^2 I then used the moment of inertia given in the problem to solve for torque. T...
  16. T

    Questions about using an Inertia Wheel to apply a compressive linear force

    Summary: How to define dimensions of an inertia wheel Firstly, I have been working in aviation industry, making me to involve in the Physics a lot. For the last few weeks, There have been a problem to solve since the manfacturer had not wanted to help us by not sharing information. We have...
  17. S

    A thought I had about inertia, and derivatives of acceleration

    Well, I just had this thought earlier, and I want to share it. Here it is. So, we all know about inertia, right? The resistance to acceleration, or change in motion. Well, there is also a concept about derivatives of acceleration, mainly jerk and yank. If you don't know, jerk is said to be the...
  18. Yalanhar

    Calculate the rotational inertia of a solid hexagonal

    What I did: ##\frac{dm}{dA} = \frac{M}{\frac{3\sqrt3 R^2}{2}}## ##dm = \frac{2M}{3\sqrt3 R^2} dA## (1) ##dA=3\sqrt3 rdr## (2) (2) in (1) ##dm = \frac{2M}{3\sqrt3 R^2} 3\sqrt3 rdr## Now in the integral ##I = \int \frac{r^2 2Mrdr}{R^2}## How can I solve the integral interval? I think I...
  19. J

    Moment of Inertia: Thin Spherical Shell

    Homework Statement: Derive the formula for the moment of inertia of a thin spherical shell using spherical coordinates and multiple integrals. Homework Equations: Moment of Intertia is (2MR^2)/3 I = (2MR^2)/3
  20. dlxgains

    Moment of inertia project help- experiment 1: Bifiler Rod

    Homework Statement: So i need to find equations to help me with a bifiler suspension experiment in which i will use a rectangular drop bar as the oscillating object, also any help with the method of this experiment would be greatly appreciated. The end goal is to find the moment of inertia...
  21. carter7gindenv

    Thermal inertia vs effusivity, what is the difference?

    Hello, I'm slowly getting crazy about this stuff. I'm trying to understand what are thermal inertia/effusivity and information have been incoherent so far. The best example of that is seen on wikipedia where the only mention of thermal inertia is in the article...
  22. A

    What is the direction of the torque in this scenario?

    I=(1/2)(6kg)(0.4^2 + 0.52^2) = 1.29 kg*m^2 initial: 34 mph= 15.2m/s 15.2m/s = (ω) (0.52m) ω= 29.2 rad/s after: 19 mph = 8.5m/s 8.5m/s = ω(0.52m) ω= 16.3 rad/s acceleration = (16.3 rad/s - 29.2 rad/s) / 5s= -2.58 rad/s^2 torque= |-2.58 rad/s^2 |(1.29 kg*m^2 ) = 3.3 N*m I am confused...
  23. Heyxyz

    Moment of Inertia: Car vs Sphere

    Hello, I tried to put it in an equation, but it didn't really work out. In this situation, the car was about the size of a model, and, while not exact, the radius of each wheel couldn't have been more than like a centimeter. Conversely, the ball was like twice the size of the car and had a...
  24. A

    Torque and inertia of a wooden rod

    ∫ λ(x)=0.2 kg/m + 0.061(x/L)^2 kg/m = 0.2(x) + (0.061/3) (x^3) /(1/L^2) mass of rod = 0.2+ (0.061/3) =0.22 kg inertia of rod through nail = (1/3) (mass) (L)^2 inertia of rod through nail = (1/3) (0.22kg) (1m)^2 = 0.073 kg*m^2 torque magnitude = (53N) (0.5m) = 26.5N*m angular...
  25. A

    Torque and inertia of a space object

    I= 524kg * 6m^2 = 18.86E3kg*m^2 KE=(1/2) (18.86E3kg*m^2) (0.16 rad/s )^2= 241.5 J torque= 0.25* 57N* (6m)=85.5 N*m
  26. jisbon

    Moment of inertia of 2 uniform thin rods

    So to start off, what I will do find the center of mass of each of the rods. So for the top rod, COM is at where y= 0.5 L and COM of the rod at the bottom is at x = 0.5 L. From there, how do I proceed in finding the moment of inertia using parallel axis theorem? Do I simply treat: ##I...
  27. FluffCorgi

    Rotational Motion and moments of inertia

    I have the moment of inertia for the core(initial) and full body(final) but my answer for the moment of inertia for the arms(initial) was incorrect. Arms(initial) moment of inertia:(1/12)(6)(1.7^2)=1.445 this is incorrect for some reason Core(initial) moment of inertia: .9558 Full...
  28. kepherax

    Moment of Inertia of a Rectangular Picture Frame

    https://www.physicsforums.com/attachments/250905 I know the answer, but am not certain how they got Lsin(angle) for R?
  29. F

    Momentum of intertia for a dihydrogen molecule

    I don't know if the value for distance between protons given in the homework is right (##d = 74.14 pm##). Indeed, on the following link : https://brainly.in/question/7147660 , they take a distance equal to ##d = 4\times10^{-10} m##. In all cases, the same formula is applied ...
  30. S

    Motion of a spool of thread on an inclined plane related to inertia

    a) Describe the motion of the spool: it will roll down the plane, rotating counter clockwise. I am confused when setting up equation of torque. If I take center of the spool as pivot, only the tension of thread produces torque but the direction will be clockwise and it makes the spool will move...
  31. jisbon

    Moment of inertia of this shape about the x-axis

    I've attempted this question, but the answer seems to be incorrect. Here's my workings: ##I=\int y^2 dm## - standard equation ##dM = \mu * dy * x## - take small slice and find mass of it ##x = 4y-16## - convert equation in terms of x to sub in later ##dM = \mu * dy * 4y-16## ##I=\int y^2 \mu *...
  32. Kaushik

    Moment of Inertia of a hollow sphere with Mass 'M' and radius 'R'.

    Homework Statement: Derive the formula for moment of inertia of a hollow sphere. Homework Equations: Required answer ##\frac{2MR^2}{3}## Consider a Hollow sphere. At an angle ##Θ## with the vertical, consider a circular ring whose moment of inertia is given by ##MR^2##. The most basic...
  33. G

    Dumb question about inertia and rotational inertia

    Consider two bodies, A and B, of equal mass set at a short distance. Body A is spinning and body B is at rest. Then, through some kind of electromagnetic device, a strong repulsive force is established between them. Will both be displaced at the same speed?
  34. C

    Spinning a bucket of water in a vertical circle - Inertia

    Homework Statement: How or why does inertia caused the water in a bucket not to fall out when spinning in a vertical circle. Homework Equations: Is the bucket catching the water? I know Inertia is the resistance of any physical object to any change in its velocity.
  35. C

    How does inertia cause the water to stay in the bucket

    Homework Statement: How or why does inertia cause the water to stay in the bucket while spinning it vertically? I know inertia is the tendency of an object to remain at rest or in a state of uniform motion, but I am not exactly sure how it causes the water to stay in the bucket while it is...
  36. naji0044

    Rotational inertia - globes connected by a thin rod

    Problem Statement: Finding the rotational inertia Relevant Equations: I=∑m*r^2 A rigid body of 2 massive globes with homogenous mass distribution and a thin rod is connecting the 2 globes. The globes has radius R1 = 0.18 m and R2 =0.28 m and masses m1=193 kg and m2=726 kg. The thin rod has...
  37. VVS2000

    Bicycle and tackling inertia at higher speeds

    Thanks in advance
  38. Benjamin_harsh

    Moment of Inertia: Calculation Method

    Ratio of moment of inertia of a circle and that of a square having same area about their centroidal axis is: Sol: both area and square have same area: ##a^2 = \large\frac{π}{4}\normalsize d^{2}; \large\frac{d}{a} =\large \sqrt\frac{4}{p}## Ratio of moment of inertia of a circle and that of a...
  39. P

    Determining the Moment of Inertia about an angle θ to the x axis

    I thought about solving it using components of IAB but since it is a scalar quantity it doesn't seems to be correct . I don't think Perpendicular Axis theorem will work as required Inertia is in the same plane.
  40. Benjamin_harsh

    Exploring the Mystery of Moment of Inertia

    While I am reading this article, it says moment of inertia is same at radius of ring and at the center of it. How is that possible?
  41. Physics lover

    Moment of inertia of a square along an axis inclined at an angle

    My attempt-:I extended the axis and made a triangle by joining other adjacent vertex to the line such that its angles are 15°,75° and 90°.I found the distance between the centre of square and upper vertex of triangle by using law of sines.And then i found out inertia along upper vertex of...
  42. G

    Does the mass of an object affect its inertia?

    I know what the answer is supposed to be, but I don't understand why. Here is my logic as to why I thought a few of these suggestions should be the right answer. "C) Mass is a measure of an object’s ability to resist motion or movement of any kind." Considering F = ma, and that mass is...
  43. L

    Spinning top's moment of inertia I (disc on shaft )

    I hope you guys can help me with this problem.. A top in the form of a flat, circular disc spins on a shaft that is inclined at an angle alpha to the vertical. Now I have to find the moment of inertia I for the disc about its centre on the shaft. My attempt was building I with spherical...
  44. EEristavi

    Energy Conservation in Angular motion / Moment of Inertia

    I write Conservation of Energy: Potential Energy loss(change): U = m g ##\Delta##h = m g (R+r) (1-cos##\alpha##) kinetic Energy gain(change): K = (##\frac {m v^2} 2## + ##\frac {I \omega^2} 2##) + (##\frac {M v_2^2} 2## + ##\frac {I_2 \omega_2^2} 2##) U = K m g (R+r) (1-cos##\alpha##) =...
  45. I

    General Physics I Question: Moment of Inertia Problem Difficulty

    Hi everyone, I am honestly pretty confused as to where to start with this. Can anyone give any pointers as to where I could possibly go, for (a) and (b)? Thanks!
  46. R

    Rotational Inertia: Calc. & Guidance Needed

    This question is ridiculously complex for me. I know how to find the Inertia if it was a rod ##I =\frac{1}{12} ML^{2} = \frac{1}{12}(0.000104)(1.6900)^2 =0.00002475 kg * m^2## To find the Inertia for the individual disks I am having trouble. Not sure how to add them all up together. Guidance...
  47. EEristavi

    Why Do I Need to Sum All the Torques Along the Radius for Calculating Torque?

    Only problem I have is in calculating Torque I say: dT = R dF = R k g dm & dm = ##\frac m {\Pi R^2}## R dr d##\theta## However, in the solution I see that: dT = r dF = r k g dm & dm = ##\frac m {\Pi R^2}## r dr d##\theta##I don't get it: when taking the whole T (when I integrate), why do I...
  48. EEristavi

    Calculating the moment of inertia of Cone

    I'm Summing the Inertia of "donuts" with width dr and radius - r. I'm also "flattering" the cone into 2D and considering that each donut has different mass - because of the different height - h so: dm = 3 m h / (pi R2 H) dr I = ∫ dm r2 = 3 m h / (pi R2 H) r2 dr from triangle similarities H/R...
  49. R

    How is moment of inertia calculated and translated between units?

    Calculating moment of inertia and translating it between units, I've become confused. The example is a mass of 1kg at 2000mm from the pivot. The force is applied at 1000mm from the pivot. Basics as far as I'm aware: Moment of inertia = mass * Distance to center of rotation^2 Torque = Moment...
  50. S

    Are momentum and inertia definite ?

    If an object is moving it has momentum .. but if the frame of reference is altered so the speed matches, the momentum apparently vanishes (?!). Likewise with apparent inertia during acceleration of an object - similar acceleration of the frame can radically alter the perceived affect. Can...
Back
Top