# Questions tagged [inertia]

Inertia is the tendency of a body to oppose changes to its state of motion. DO NOT USE THIS TAG for moment-of-inertia!

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### Angular velocity of disc from induced motion

I came across a question regarding linear momentum $L$ and it's conservation, however I tried and got confused. It reads: A $40kg$ girl stands on the very edge of a rotating disc of mass $50kg$ and ...
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### Why does things travel in a straight line in inertial frames?

Why does physical entities travel in straight paths in a flat space-time and in geodesic in curved spacetime? Is it due to Inertia? If it is, then why does waves also follow the same pattern?
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### Doubts About Force and Inertia!

But then what does inertia mean at all!? Cant we calculate how much it resists the applied force? I mean considering an imaginary plane with no friction but gravity as of Earth and an enormous mass of ...
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### Isn't inertia experience by person in moving bus is Torque

When a bus moves suddenly, the person standing in it tilts backwards. This concept is explained using inertia (tendency of body to resist change in its state of motion) but when the bus moves suddenly,...
5k views

### What causes a rotating object to rotate forever without external force—inertia, or something else?

Someone told me that it is not inertia, but I think it is inertia, because it will rotate forever. In my understanding, inertia is the constant motion of an object without external force. Am I wrong?
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### Do electromagnetic fields have inertia? Or, what sets the speed of light?

In all mechanical waves, there is a restoring force and an inertial influence. For example, a plucked string oscillates because the restoring force brings it back to being straight and then the string'...
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### Does horizontal inertia affect the time it takes something to reach the ground?

I am new to physics. I’m confused about how an bullet shot horizontally would land at the same time with as a bullet dropped vertically (ignoring air resistance and the curvature of Earth). Having ...
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### How would inertia work in an elevator?

If we imagine standing on a scale inside an elevator, the scale will project our weight. As the elevator starts to move downwards we will not start to move downwards immediately; because of inertia we ...
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### Is there still no known origin of the law of inertia?

To quote Feynman at about the 21 minute mark of the first Messenger Lecture on The Character of Physical Law, ...that the motion to keep it going in a straight line has no known reason. The reason ...
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### Mathematical model for transition from mass to energy put in layman's terms [closed]

Mass and inertia are interchangeable, but no intuitive explanation of mass being different for the various particles is known to me. The question I have is: since mass and energy are interchangeable, ...
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### Weight and Inertia (are they related?)

R. Feynman wrote in his lecture (The Feynman Lectures on Physics: Chapter-9) "Weight and inertia are proportional, and on the earth’s surface are often taken to be numerically equal, which causes a ...
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### Inertia as a fundamental interaction

Why is Inertia not included as one of the fundamental interactions, yet gravity is included as one of the four known interactions, and there is an equivalence established between gravity and inertia.
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### Can an object spinning near the speed of light be accelerated significantly in any direction?

This question made me curious. It refers to a ball which is rotating so that its equator is approaching the speed of light, then talks about what it would look like if the observer moved. What I'm ...
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### If inertial mass were equal to for example half of gravitational mass why would things not still fall at same rate?

I have read that it is the equality of inertial and gravitational mass that causes all objects to fall at the same rate irrespective of size. But if this were not true, what effect would we see? Would ...
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### In zero gravity!

If spacecraft moving in a stable speed or acceleration suddenly stopped would an astronaut continue moving forward (such as a man in a train) ?
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### How can a flywheel make engine run smoothly?

In the video Moment of Inertia Demo, a man states that moment of inertia will be higher if the masses are away from the axis of rotation. The engine take more power to spin the flywheel, because of ...
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### Inertia Vs Momentum

At my recent lesson on kinematics, my teacher taught about inertia and momentum. This is what she said. Inertia: a characteristic of an object that resists changes to its state of motion. Momentum: ...
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### Where exactly is inertia stored? [closed]

Suppose you have the power to take a snapshot of an object containing all its information. Say a ball was thrown to a direction to your right and you took a snapshot of it. This snapshot contains all ...
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### How does an atom's electric field overcome an electron's inertia?

An electron has mass, and therefore has inertia. How does an atom's electric field perpetually overcome an electron's inertia, necessary to hold it in its shell? Does this require continual work to be ...
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### Isn't inertia experience by person in moving bus same as torque

When a bus moves suddenly, the person standing in it tilts backwards. This concept is explained using inertia(tendency of body to resist change in its state of motion) but when the bus moves suddenly, ...
140 views

### Will anyone please explain this problem using 4 fundamental forces?

If there are only four fundamental forces (gravity,e.m.,strong,weak) in the universe and all other forces can be expressed as a function of them then consider this problem. Suppose I throw a particle '...
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### Looking for ways to transform time-series data recorded from object movement into equation describing the movement direction of the object

Looking for some time-series data transformation advice! I want to know what's the best way to transform data of 9-tuples time series data of IMU (Inertia Measurement Unit) sensor, recorded from a ...
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### What if Force was not Mass times Acceleration? [closed]

We know that Force equals Mass times Acceleration, $F = ma$. But what if we had a law like $$F=m^2a$$ or $$F = 2ma~?$$
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### Why is the ratio of gravitational force and the inertia to resist it 1?

Is there a deeper meaning behind how things of different mass fall at the same acceleration? It feels so perfectly balanced...
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### When do we illustrate inertial forces on inertial frames of reference?

I came across two practice questions wherein an object was attached to an accelerating vehicle, yet only one of these cases required an inertial force to be illustrated on the object's free body ...
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### How does the inertia of granules within a rotating cylinder affect its inertia?

If a cylinder is partially filled with granules and is rolling down an inclined plane, is there any relationship between the rotational motion of the granules and the motion of the cylinder? I'm ...
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### Why does mass cause resistance to acceleration?

If I were in a vacuum with no gravity or friction, why would it be harder to push a floating bowling ball than a marble? Is there anything happening on an subatomic level that makes matter act ...
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### Why doesn't a ball thrown upwards fall behind us if we're moving forward?

If we consider ourselves traveling in a bus and if we a throw a ball upwards, the ball should fall behind us according to law of inertia, right? If so why doesn't the ball always fall behind us each ...
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### Convert inertia formula to excel calculator

I've been looking at this question: "Weight" of moving object in a car collision but to be honest I can't get my head around how to work it out myself (I'm not a physics student!). What ...
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### How Is the Inertial Mass Different From the Gravitational Mass? [duplicate]

I recently read that the mass that we deal with in the equation $F=M_{i}a$ is called the inertial mass and the mass that we deal with in $F=M_{g}g$ is called the gravitational mass. I find a hard ...
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### How did Newton prove the equivalence principle with pendulums?

I know pendulums may be equivalent to a free fall but I would appreciate any further explanation for it.
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### Spiral lamp chane state speed [closed]

Question is how fast halogen lamp reach it full temperature, going from cold (not light) state to full light emit state. how fast in milliseconds it takes, imagine: if led lamp work instantly like 0 ...
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### Inertia of a falling weight

I use a standard device (penetrometer) that uses a 10 kg weight that is dropped a constant distance to cause a probe to penetrate soil. The penetration distance after 4 blows is recorded. If I were to ...
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### Relation between Fisher Information Matrix and Inertia Matrix

I have been wondering whether there is a relation between the Fisher Information Matrix in a stochastic particle system and Inertia Matrix?
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### Calculating inertia of motor

I'm currently working on a project, and for futher calculations down the road (the controller of the mechanical system) I need to calculate, as accurately as possible the interia of the system. I'm ...
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### Which fundamental force underlies inertia? [closed]

We learn about the four fundamental forces (gravity, electromagnetism, strong, weak). I am curious about how these four forces mediate/cause/drive everyday phenomena. In particular, it has never been ...
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### Why is Quantized Inertia considered pseude-science? [closed]

In the criticism section of the Wikipedia article to Quantized Intertia it is stated that QI is considered pseudo-science. Unfortunately none of the linked but in none of the provided links can I find ...
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### Does “Quantized Inertia Theory” violate conservation of momentum? [closed]

This recent news article reports that DARPA is doing work with "quantized inertia", despite their claim that it's not widely accepted by physicists: The Defense Advanced Research Projects Agency (...
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### Cube tumbling over

When a moving cube hits a low step (the step is perpendicular to its velocity) and tumbles over, is its angular momentum conserved? It is implied that it is so, but certainly gravity produces a torque ...
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### If centrifugal force is fictitious, what force is real in its stead?

Here's an example illustration: The way I understand it, when the car starts turning, the centrifugal force at first does not exceed the force of friction, which allows the car to stir. But at some ...
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### What really is “inertial force”?

In Fluid Mechanics we often see the term inertial force when discussing Reynolds number. The problem is, I didn't really get what's this inertial force. Basically, the notion of inertia I have is that ...
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### Calculate stroke force and angle for a ball rolling on a surface to reach a destination position (optimal golf putt)

I'm trying to find an algorithm which calculates the optimal golf putt (angle, force) given a 3D surface (obtained through Poisson reconstruction), start and destination position (hole). I guess that ...
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### Transfer of momentum from a wave to it’s waveguide based on theta and the inertia of the wave?

Bit of a complicated one - I've been trying to understand how the energy in a wave dissipates or transfers it's energy to the walls of a wave guide as the angle of the wave guide changes. As the ...
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### Couldn't we always redefine units so that inertial mass and gravitational mass are equal?

It is a known fact that inertial and gravitational masses are the same thing, and therefore are numerically equal. This is not an obvious thing, since there are even experiments trying to find a ...
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### What is the relationship between gravity and inertia?

What is the relationship between Gravity and Inertia? Einstein told us that gravity and inertia are identical. And from the fact that two different masses fall at the same rate, I believe we can say ...
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### What is meant in mass' definition 'resistance to acceleration'? [closed]

Wikipedia: Mass is both a property of a physical body and a measure of its resistance to acceleration What does this mean? I know of the $E=mc^2$ formula. I think, the energy required to '...
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### Inertial and non-inertial frame

How to define an inertial frame of reference mathematically? I want a definition with proper chosen coordinate axis which will help me to differentiate it with the non inertial ones. I have been ...
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### Why is Disturbance Force Equal to Total Force in Stokes Flow?

So this step confuses me. Why is it true that the disturbance force is the total force in stokes flow? Any advice or guidance would be great! From Pozrikidis' book: