# Tagged Questions

Newtonian mechanics covers the discussion of the movement of classical bodies under the influence of forces by making use of Newton’s three laws. For more general discussion of energy, momentum conservation etc., use classical-mechanics, for Newton’s description of gravity, use newtonian-gravity.

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### Why doesn't an object, despite having a non-zero potential energy stored in it, fall by itself from the elevation?

When an object is at a certain height, it has some energy stored in it as we have done some work on it to get it to that height. So when it already has energy, then why doesn't it fall off from the ...
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### Why does the water in a bucket stay even when swung around in circular motion? [duplicate]

What are the force that act on the water and which force is responsible to keep the water from falling out?
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### Which formulas can be used instead of $\frac{1}{2}kx^2=\frac{1}{2}mv^2$, when we are solving a mathematical problem related to horizontal spring? [closed]

Let, contraction of a horizontal spring, $x$, is $4$ cm and mass of a bullet, $m$, is $10 g$. Spring constant, $k$, is $200 N/m$. When bullet leaves the gun, what will be the velocity of it? Can I ...
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### Problem understanding this

Let's say a body $a$ applies a force $\vec F_b,_a=\vec F$ as shown in the figure. so according to the third law the body $b$ also applies $\vec F_a,_b = - \vec F$ so the bodies start rotating about ...
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### When does the shifting of normal force occur?

I recently learned that normal force often shifts from it's usual line (bellow the COM) to counter the torque produced by friction. Is this shifting only possible when friction is there ?
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### Work energy theorem: variation of kinetic energy as sum of terms given by the work of single forces

Work-energy theorem states that $$W_{\sum F_i}=\Delta K,$$ where I expressed with $W_{\sum F_i}$ the work done by the resultant of forces ${\sum F_i}$ and with $K$ the kinetic energy. In general it ...
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If I am sitting inside a closed sphere (I can't see the outside), can't I feel when the sphere is at constant speed ? Can I feel when it is accelerating ? Why ? The defination of force given ...
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### Sphere through Torus

In the following picture (it's awful) , What would happen if the sphere and the torus (the sphere can pass through the hole of the torus) are left in an empty space ? I assume (I am probably wrong) ...
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### Determine what type of force that correspond to a springs-masses system

I am working a question from my Applied Math class, there is a question asked me to determine what kind of force correspond to a springs-masses system. I have two forces, $f_1=1$ and $f_2=-1$, spring ...
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### Understanding the derivation of equation of motion in rotating frame

Next, we consider how the change of any vector during a small time-interval $\Delta t$ can be expressed as the vector sum of two contributions: The change that would occur if it were simply a ...
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### Photoelectric effect – What is the probability of a photon absorbtion by an electron?

Is it correct that each photon above threshold frequency is absorbed by an electron What is the probability of a photon absorbtion by an electron? Can a quantitative example be given?
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### Pressure or confusion

We all know that pressure is force per unit area. for example we have a pressure of $5N/m^2$, so is the load of $5 N$ acts on the entire area or it acts just at a point i.e. is the load a point load ...
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### Newtons corpuscular theory

I am learning about the history and evolution of certain physics theories, one being Newtons corpuscular theory. I am reading that Newton predicted the corpuscles, which make up light would travel ...
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### What's the required tensile strength for a wire?

I want to horizontally stretch a 50 meters wire rope and slide 100 kg object from side to side. What should be the minimum tensile strength (or carrying capacity) of the rope to be able to hold the ...
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### Interpretation of elastic modulus in a light elastic string

A light elastic string with elastic modulus $\lambda$ and natural length $a$ is fixed at one end at a point $O$, and a particle of mass $m$ is attached at the other end. The particle moves in a ...
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### Can a body under weightlessness detect if it's under free fall or under a zero gravity field?

My first thought was to use an accelerometer. However, quoting from wikipedia, an accelerometer at rest on the surface of the Earth will measure an acceleration g= 9.81 m/s2 straight upwards. By ...
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### Force required to spin a platform around a non-centered axis

This might be a silly simple question, but I cannot confirm the correct answer. Situation: I am building a wall bed and i need to calculate how much force will be needed to lift it from a horizontal ...
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### What happens to Newton's Third Law during the reflection of a pulse from a free end?

Well, it is known that a pulse gets inverted when it gets reflected from a fixed support while the polarity of the pulse remains same when the incident pulse gets reflected from a free end. However, ...
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### Work done by a force

What is the difference between work done by a force and work done against that force? Is it true that work by a force = -(work against that force)?
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### Why are electrons treated classically in cyclotron measurements?

As I understand , systems having large angular momenta relative to the planck constant (limit of large quantum numbers, e.g. $J/\hbar \to \infty$), can be treated as classical systems. Now in the case ...
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### Work-energy theorem for a system

While studying energy conservation on Morin I found this explanation about the work-energy theorem for a system. The work–energy theorem stated before is relevant to one particle. What if we are ...
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### Why does force cause acceleration?

Consider a ball placed on a smooth plane. If you take a plank made out of wood and whack it (apply a force on it), does it accelerate because First, the force compresses the part of the ball in ...
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### The definition of the unit of Force

Below, I quote what my physics textbook says. $$F=kma$$ The units of force are so chosen that this constant of proportionality, $k=1$.Therefore $F=ma$. For this, one unit of force is defined ...
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### How I think about rolling [closed]

Below, I have written how I think about rolling. I wish to know if my idea as to how it works is correct. Consider a rigid ball on a plane which has considerable friction. If you push the ball ...
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### Force and Torque

Think of a uniform sphere. Sometimes if a force is applied to the sphere it does not only move but also spins. So there is a torque. But is it possible to calculate which part of the applied force is ...
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### Physical meanings of kinetic energy

While studying energy on Sears & Zemansky's University Physics, I came up with a doubt on the meaning of kinetic energy. The book gives two possible physical interpretations of this quantity. ...
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### What Magnitude(db) and Phase(deg) represent on Bode Diagram?

What Magnitude(db) and Phase(deg) represent on Bode Diagram? I am working on 2 DOF System and I want to understand some basic things. Below (on the picture) you can see the system, the transfer ...
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### How is hemispherical shell any different from a semi-disc in terms of center of mass? [closed]

If we shift all the rings that make up the hemisphere parallel towards the center then it will build up two semi-disc .. But we know that We can also explain it by saying that if we take the shadow ...
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### Why charge is not a measure of inertia?

We know that mass is the measure of inertia of rest. Then why charge is not a measure of inertia? What causes the difference between charge and mass?
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### Why is the definition of inertial mass circular?

On Wikipedia, the definition of inertial mass is: Inertial mass is the mass of an object measured by its resistance to acceleration. And, can be evaluated using $F = ma$, Newton's second law....
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### Is torque necessary in rigid body mechanics? [duplicate]

Suppose we have a weightless, rigid rod fixed at one end, but free to swing at the other, where there is a mass $m$ attached. If we want to determine the tangential acceleration of the mass using ...
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### Angle of a pendulum as an explicit function of time

What would be the solution for the angle $\varphi(t)$ and angular speed $\omega(t)$ on pendulum without the small angle approximation - not as differential, but as an explicit function of time? The ...
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### Why do travelling waves continue after amplitude sum = 0?

My professor asked an interesting question at the end of the last class, but I can't figure out the answer. The question is this (recalled from memory): There are two travelling wave pulses moving in ...
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### Help me understand this simple linear momentum [closed]

A 40.0-kg skateboarder on a 3.00-kg board is training with two 5.00-kg weights. Beginning from rest, she throws the weights horizontally, one at a time, from her board. The speed of each weight is 7....
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### Force acting on a pole which is fixed with friction [closed]

A uniform pole of weight 50kg is balanced in the vertical position. The length of the whole pole is 6m.the pole is fixed at point C on the ground.A force 500N is applied at B which is 2m from C. If ...
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### Scenario where Newton's 3rd Law breaks down

In Kleppner and Kolenkow's Introduction to Classical Mechanics, it reads, One system that is particularly troublesome for our present formulation of Newtonian mechanics is the electromagnetic ...
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### Understanding Feynman's argument about Stevinus

In the Feynman lectures vol 1, chapter 4, he mentioned a "Brilliant, clever" way of solving a problem named: A simple example is a smooth inclined plane which is, happily, a three-four-five ...
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### Quantum mechanics of the electron in an atom vs. Gryzinski's free-fall atomic model [closed]

According to Heisenberg's Principle of uncertainty, you can not know the place and speed of a particle, at the same time. You only have probabilities of the estimate values. These probabilities forms ...
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### Why do wheels spin?

I'm pretty sure this is probably a stupid question but it is annoying me a lot. In my physics textbook it says, cars move because the wheels exert a backward force on the ground and the ground exerts ...
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### How does rocket thrust work?

I can't seem to find a specific answer to this anywhere. I understand that in a rocket there is a chemical reaction that causes gas particles to leave the rocket at high velocity. By Newton's third ...
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### Why isn't the entire force we apply on two objects transmitted to the second object?

When we exert a force of X N on a box in contact with another identical box on a frictionless surface, the resultant force on both boxes is 0.5X N. My question is, why doesn't the first box push the ...
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### How to predict the group velocity of the waves in the liquid?

The question appeard in the book. The phase velocity of the waves on the liquid surface is given by $$V_{ph}=\sqrt{\frac{2*\pi S}{\lambda \rho}}$$ where S is the surface tension and $\rho$ is the ...
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### Car Crash Question… (Conservation of Momentum?) [duplicate]

Dumb car crash question. I think this is a conservation of momentum problem. In one scenario, two 4000 lb cars (car A and car B) each traveling at exactly 35 MPH in opposite directions have a ...
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### How can planes land on a rotating Earth?

If the earth is rotating (e.g. at 1000km per hour, at the equator), how can planes safely land on a moving runway?
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### Books on Celestial Mechanics [duplicate]

My background is mathematics. I would like to study celestial (not classical) mechanics and looking for an appropriate book. I found that somebody has already asked a similar question "How to learn ...
I was trying to find power to mass ratio of sun (work done per second at each unit mass at average), but I found the unit is quite straight: $W=kg \space m^2 s^{-3}$ Then $W/kg= m^2 s^{-3}$ Which ...
We are given an undamped simple harmonic oscillator, and two positions $x_{1}, x_{2}$ with the corresponding velocities $v_{1}, v_{2}$. We want to find its frequency in terms of the $x_{i}$ and $v_{i}$...