# Tagged Questions

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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### Why is centrifugal 'force' perpendicular to line of inertia

I know that centrifugal is labeled a fictitious force only arising in a rotating reference frame, but I still struggle to understand the forces at play intuitively in tethered rotating bodies. I've ...
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### How is inertial mass different from gravitational mass? [duplicate]

I recently read that the mass we deal with in Equation $F=M_{i}a$ is called inertial mass and the mass we deal with in $F=M_{g}g$ is gravitational mass. Suppose I take a ball in a free fall and in ...
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### Block on an incline moving right with an acceleration [closed]

The situation looks as follows: The incline is moving rightwards with a constant acceleration The forces on the picture are: mg - weight, N - normal force, F - inertial force (already shown), ...
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### How do I calculate the experimental and theoretical rotational inertia of a point mass?

I'm getting some weird results from a calculation I'm doing and quite honestly, I'm pretty sure it's due to human error. I do have an apparatus involved for the experimental process for my lab but I ...
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### Perceived sway difference between double-decked vs. single-decked buses?

Why is that when I'm standing in a moving double deck bus, my body doesn't move a lot; whereas, in a moving single deck bus, my body moves quite a bit? It seems like I swing a lot in single deck buses,...
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### Relative motion question [duplicate]

I'm sitting on my seat in a train and the train is moving at a very high speed, let's say 600 mph. If I throw a ball vertically up in the air (while still sitting on my seat), will the ball fall back ...
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### Will larger balls make a Newton's cradle swing more stable?

I got a rather small Netwon's cradle and when I start it, the effect is not very good since all the balls start to swing where the effect we want is obvious. The balls are small and I wonder if larger ...
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### Inertia and Rocket Propulsion

We were taught in school that the law of inertia indicates that an object tend to stay the way it is, so if you throw something in space it will tend to go on forever and ever. The reason an object ...
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### If there is no gravity, does that mean there's no mass as well? [duplicate]

I have demonstrated that weight only is measured based on the gravitational pull of where you live. For example, the gravity on the surface of Mars is three times smaller than the gravity on the ...
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### “Weight” of moving object in a car collision

From time to time I see safety warning about keeping loose items in your car. The last warning used a 2kg object, and claimed that if a collision occurred at $50{km\over h}$ it would have a weight ...
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### Is inertia present in a body while in state of motion?

According to Newton's law of inertia (written in book:The Mathematical Principles of Natural Philosophy**) it is said that in all objects having mass, have always inertia included in their property ...
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### Doubt in law of mutual interaction

Book: Classical mechanics (textbook) by Douglas Gregory (cambridge publications) Law of mutual interaction states that when two particle (let it be P1 and P2) interacts, the particle (P1) induces an ...
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### Can inertia be explained by Bremsstrahlung?

Considering that on the atomic level objects consists of densely spaced positively and negatively charged particles, does not the acceleration of those objects lead to Bremsstrahlung of those ...
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### Velocity of 2 balls with different masses on a moving train after the train brakes

Question This is from my textbook: There are 2 balls of the same size made of rubber and iron respectively kept on the smooth surface of a moving train. Which ball will move faster when the train ...
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### Does trade affect Earth's rotation? [duplicate]

Every country is trading with other countries around the world, some more than others. I was wondering if there would be any change to the Earth's rotation because of the imbalance of trade between ...
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### Why does inertia happen?

In this video R P Feynman relates a story where his father told him that, even though we know the word "inertia" and what it means, nobody knows why inertia happens. Is that still true?
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### Can someone explain to me inertia?

I'm a little new to physics and I'm not quite getting the concept of inertia. Can someone help me?
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### Does inertia increase with speed? [duplicate]

I have heard that when the speed of the object increase, the mass of the object also increase. (Why does an object with higher speed gain more (relativistic) mass?) So inertia which is related to ...
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### Closed-form equation for orientation and angular velocity over time

If a rigid body, rotating freely in 3d, experiences no friction or other external forces and has an initially diagonal inertia matrix $\mathbf{I}_0$ (with $I_{11}>I_{22}>I_{33}>0$) and ...
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### What truly is mass, and is there a direct way to measure it?

We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
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### A man running on the treadmill

Imagine a man is running on a treadmill. His inertia with respect to floor will be zero because he is not moving with respect to floor. If both he and the tread mill suddenly stops he will not fall, ...
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### Does Unruh Radiation replace the cosmic horizon radiation?

A recent paper, titled Inertia from an Asymmetric Casimir Effect, discusses the universal horizons relative to an accelerating observer (Rindler space). A figure it used to demonstrate its point ...
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### London into Australia in 90 minutes

Me and my friend are having a debate on whether it would be possible for a human to travel at 15,000 miles an hour from London to Australia in the matter of 90 minutes. Would a human be able to ...
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### How does liquid in a ball affect its rotational acceleration down a ramp?

Suppose we have a shell with mass $M$ and radius $R$. If we let that roll without slipping down a ramp of angle theta to the horizontal, we can easily find the acceleration of the shell the instant ...
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### Force and Torque Question on an isolated system [duplicate]

If there's a rigid rod in space, and you give some external force perpendicular to the rod at one of the ends for a short time, what happens? Specifically: What dependence does the moment of inertia ...
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### In a spaceship, if a vessel suddently stops will an object inside the vessel keep going?

My question is a 2 part question. First if a vessel in space is going very fast and suddently stops (maybe it is not possible but that is not the point) will things/humans inside the vessel keep ...
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### Calculate Rotational Intertia

If a can of soup, and a can of beans (tightly packed), are set in a race down a rough hill (has friction), the soup wins, because the inside of the can (soup) is not drawing energy from the system. ...
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### Why is $F = mg - T$ in this case?

The situation is as follows: I am told that $F_{net} = mg - T$ in this case, but doesn't that not take into account that $T$ isn't applied to the center of mass? Newton's second law is defined for ...
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### Tensions And Pulleys With Masses

The problem I am working on is: "A block of mass m1 = 1.80 kg and a block of mass m2 = 6.30 kg are connected by a massless string over a pulley in the shape of a solid disk having radius R = 0.250 m ...
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### Two Different Sorts of Inertia: Inertial Mass and Moment of Inertia

There are two different sorts of inertia: inertial mass and moment of inertia. I am currently reading about moment of inertia. Now, I know inertia is an important concept; with it, we can determine ...
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### What is the present state of Mach's Principle amongst physicists? [duplicate]

Possible Duplicate: Is Machâ€™s Principle Wrong? I'm doing research on gravitation and inertial forces and would like to know what is the place that Mach's Principle is occupying nowadays in the ...
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### Is Earth's orbit altered by recoil from take-off/launch/recovery of aero/space vehicles?

Just what the title states. Pretty much all movement on Earth is by pushing against the much greater mass of Earth. Given there are easily thousands of aircraft taking flight/landing, and a lesser ...
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### Why do objects with different masses fall at the same rate? [duplicate]

Possible Duplicate: Confused about the role of mass Today we were in our Literature class talking about the Renaissance and the Enlightement and our teacher also said that scientific ...
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### Fictitious Forces $\overset{?}{â‡”}$ Constraint Forces (re: D'Alembert's Principle)

Are fictitious forces and constraint forces the same thing?
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### Why are there some inconsistencies with the underlying principle of center of gravity and rotational inertia?

COG: The lower the center of gravity, the more stable and object is. Rotational Inertia: The farther the concentration of mass from the defined axis of rotation, the more resistance the object has to ...
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### Instability of a thrown tennis racquet

Someone once mentioned to me that it's impossible to throw a tennis racquet (or similarly shaped object) into the air, perpendicularly to the string plane, in such a way that it won't turn. What is ...
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### Double gyroscope: Can a spinning pencil tumble on only one axis?

Picture an object such as item 7 on this page .. http://en.wikipedia.org/wiki/List_of_moment_of_inertia_tensors Call that the x axis and z is in to the distance. See diagram below. We are in deep ...
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### Does Dark Matter interact with Higgs Field?

Dark matter does have gravitational mass as we know from its discovery. Does it have inertial mass?
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### Why is Higgs Boson given the name “The God Particle”?

Higgs Boson (messenger particle of Higgs field) accounts for inertial mass, not gravitational mass. So, how could it account for formation of universe as we know it today? I think, gravity accounts ...
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### Does a interstellar spacecraft traveling at relativistic velocity require continous thrust to maintain velocity?

Assuming completely empty space, does a spacecraft traveling at 0.5 C require continuous thrust to avoid deceleration? If the spacecraft is traveling at 0.5 C, does it's relativistic mass act upon ...
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### Why does a ball bounce?

If an object is acted on by equal and opposite forces then it will be in equilibrium, and it's acceleration or velocity (and so direction as well) will not be changed. So when a ball bounces, it ...
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### The two faces of $F = m*a$

As I have understood, $F(t)=m \cdot a(t)$ can have 2 different meanings: When applying an external force $F$ on a point mass of mass $m$, the resulting acceleration of that mass at time $t$ is $a$...
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### Would a sneeze by a cosmonaut in a spacesuit affect his movement?

Naive question; feel free to shoot me down It is a truism that any motion in space would continue indefinitely unless it is opposed by an external force. If a cosmonaut were to sneeze within his/her ...
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### Infinite acceleration?

Why is acceleration regulated by mass? In a frictionless environment, why doesn't an object move at infinite acceleration if force is applied on it? Force causes movement, so unless there is an ...
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### Jumping in an elevator?

I've always been under the impression that jumping in an elevator wouldn't help at all, especially after reading a snippet of physics where Einstein said that free fall was identical to zero gravity. ...
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### Pushing, inertia of a cart system

I have a cart with another cart on top which gets pulled down by another cart on the side. There is no friction. The question is: How strongly do I have to push with $F$ to keep the cart $m_1$ ...
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### Is it humanly possible to change Earth's axis?

Just what the title states with the qualification that the change must be affected without using other celestial bodies as mentioned in the Clarke/Baxter SF 'Sunstorm'. Obviously given the momentum ...
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### How would you improve braking capability on a hovercraft? [closed]

Pretty much letting my mind free-wheel. Assume a fleet of air-supported hover-craft were to replace cars/etc on the streets. Assume also that the present traffic-signals/pedestrian rules remain ...