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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Is a double integral required to find the moment of Inertia of a non-uniform sphere?

Consider some ball of given radius $R$, with a mass density function that depends on the radial variable, $\rho=\rho(r)$ where $r$ is the distance from the center of the sphere. What is the moment ...
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3answers
55 views

what make the bottom portion of a wheel in rolling motion move?

As I just learn about the rolling motion which is the combination of pure translation and pure rotation. The top portion of the rolling body has the speed of double speed at the center of the object ...
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1answer
32 views

What causes the recessed blade of some folding knives to emerge in a kinetic opening? [closed]

KINETIC OPENING OF FOLDING KNIFE (FK) Several legal jurisdictions around the World, including Australia, have assented legislation/regulation which attribute the emergence of the recessed blade in the ...
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0answers
18 views

Role of the crystallographic point group on properties of tensorial elasticity

If a space point group for a crystal is known, does this automatically define the elastic tensor symmetry of the material? What further implications can be found? The crystallographic subgroups: ...
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1answer
41 views

Hooks Law and acceleration [closed]

A 435 gram sharpened piece of iron rebar into a spring loaded device. It takes a force of 355 Newtons to compress the spring by 27.5 cm. With what speed does the rebar shoot out of the device? ...
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Law of conservation of linear momentum is a consequence of Newton's forst law substantiate [closed]

Law of conservation of linear momentum is a consequence of Newton's first law substantiate.
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2answers
156 views

If Earth starts moving when attracted by an object, where does the energy come from?

Suppose a body(very big but not bigger than Earth) moves against gravitational force of Earth. The force will do negative work on the body decreasing its kinetic energy. The decreasing energy is ...
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2answers
48 views

For a massless pulley moving upwards with acceleration, is the upward force equal to the downward force?

Imagine a massless and frictionless pulley with two weights hanging either side of the pulley by a massless string. Like this except not attached to a ceiling Rather than being fixed to a ceiling, ...
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1answer
100 views

What is $g$ when traveling quickly around a planet?

I am trying to model a rocket orbiting a planet. I want to simplify the problem so that the rocket is travelling along an infinitely long flat surface with a $g$ along the $y$-axis. This is what ...
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6answers
108 views

What is the relationship between force and momentum in collisions?

I know that $ \Sigma F = \Delta mv/\Delta t$. But if we had a marble that moves in a straight line at a constant velocity and colloids with another marble. Because of the law of conservation of ...
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1answer
37 views

Surviving collapsing buildings: Which floor maximizes your chances of survival? [closed]

Although this is not a purely physical question, I think this is the best StackExchange place to ask it. When a building collapses, which floor should you go in order to maximize your chance of ...
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1answer
85 views

Why do we believe in a “force” driven universe? [closed]

Why do we not believe in the potential for a "unified force field" universe, to the exclusion of the belief in the potential for a mechanical, gear driven universe, if the correct shape for the gear ...
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1answer
42 views

Which inertial observer should I choose when using $\Delta U = -\Delta K$?

I just read and undertood that For any conservative force $F$ (which is not necessarily constant), we can define a potential energy change $\Delta U$ of an object on which the force exerts as ...
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1answer
56 views

Which moves faster in a time $t$: $A$ or $B$? [closed]

Suppose we have two objects, $A$ and $B$, both made of the same substance. They also have the same shape (e.g. two spheres), but $A$ is larger and therefore more massive than $B$. Both $A$ and $B$ ...
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1answer
43 views

Collision of a pendulum with other pendulums hanging at different heights

This is a question from a competitive test. I am not sure how to reason this out. By the length of the string, S should have the maximum amplitude. But this would be the case only when the pendulum ...
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5answers
91 views

Relation between the conservation of Energy and the conservation of Momentum?

I just learn about the momentum and it conservative attribute in a closed and isolate system and there is something I don't understand when I relate it to the conservation of the energy Considering ...
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1answer
41 views

Moment of inertia help [closed]

Okay so lets say I have a lever with 2 objects on it, object one and object 2. Object 1 has a mass of $m_1$ and is $r_1$ away from the fulcrum; object 2 has a mass of $m_2$ and is $r_2$ away from the ...
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3answers
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Underdetermined forces in a statics problem

I was trying to cook up a good exam problem on Newtonian mechanics, and I came up with one that I didn't fully understand myself. Always fun when you can outsmart yourself. In the figure a cylinder ...
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3answers
59 views

Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?

In classical physics we often cast an analogy between translational and rotational systems Force < > Torque Energy < > Rotational Energy Momentum < > Angular Momentum and considering SI ...
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0answers
25 views

Accelerating disk [closed]

A disk of radius $R$ is accelerating to the right over a plane. At $t=0$ the speed and the acceleration of the axle are $v_1$ and $a_1$ what is the velocity and the acceleration of each point (1-4 ...
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2answers
461 views

Can a box on a frictionless rotating table rotate?

I am trying to digest the following problem. Suppose a block of mass $m$ lying on a horizontal, frictionless turntable is connected to a string attached to the center of the turntable, as ...
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3answers
633 views

While finding escape velocity, does human mass counts as the mass of Earth?

Escape velocity depends upon the mass of earth. my doubt is whether human mass adds into it or not? If it add then Earth's escape velocity would be increasing!
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0answers
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How do I treat the Lagrangian in the case of a rigid body?

Here's Exercise 1.11 from Goldstein's Classical Mechanics 3rd edition (the first one after having derived the Lagrangian basically): Exercise 1.11: Consider a uniform thin disk that rolls without ...
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0answers
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Newton's 3rd Law and Equilibrium [duplicate]

What is the difference between Newton Third Law and equilibrium?
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2answers
76 views

Newtons Third Law [duplicate]

In Newtons Third Law, it states that for every action, there is an equal but opposite reaction. So that means tat for every action, there will be a reaction to cancel it out. So if that is the case ...
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6answers
626 views

Why does a conservative force return the work done against it by a body to that body?

Newton's 3rd law of motion: Newton's third law of motion or the law of action and reaction implies that there is no isolated force in nature. Whenever there is any force at all , there must be ...
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4answers
94 views

Collision paradox

Suppose an insect travelling south at some velocity, collides with a train travelling north at some other (opposite) velocity. The insect hits the front of the train, where it splats to an ...
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4answers
137 views

Kinetic energy vs. momentum?

As simple as this question might seem, I failed to intuitively answer it. Let's assume there is a $10,000$ $kg$ truck moving at $1$ $m/s$, so its momentum and KE are: $p=10,000$ $kg.m/s$ and ...
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1answer
71 views

Landau Mechanics equation 16.9

I am having trouble deriving the equation 16.9 from Landau's Classical Mechanics book. This equation is the maximum kinetic energy of a particle if a massive particle with mass $M$ disintegrates into ...
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2answers
97 views

What causes damage, kinetic energy or momentum?

Let's assume we have 2 bullets. The first bullet has $450$ $J$ of KE and $3$ $kg.m/s$ of momentum, while the second bullet has $250$ $J$ of KE and $5$ $kg.m/s$. Now if they are both shot at ballistic ...
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2answers
45 views

Line integral calculates work, even though the force from the vector field doesn't cause the movement?

I'm afraid the title here was unclear, so I'll attempt to make things a bit more clear. I am conceptually confused about the physical meaning of line integrals over a vector field, so I'll pick an ...
3
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5answers
221 views

A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?

After reading the article, I was totally perplexed . I was reading the External forces and internal energy transfers in Principles of Physics by Resnick,Halliday,Walker. It goes like that An ...
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1answer
20 views

Find force of friction on an object under influence of tension by another object

I conducted an experiment using video analyses software, and found the accleration of a box on a table being pulled by a string attached to a pulley on the edge of the table attached to the weight ...
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1answer
20 views

With what speed must e.g. a car drive into a turn so it won't drift out? [closed]

I am trying to figure out the following question: with what speed must e.g. a car drive into a turn so it won't drift out (if a turn is a circumference of a semicircle)? e.g. $r= 5 m$ $a_r= ...
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1answer
55 views

How would the solar system change if the Earth were removed

I was reading a closed question with the same title and wondered if it would be on-topic with the following change: Could a large-mass object from interstellar space pass through the inner ...
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1answer
21 views

Newton's Third Law Opposite Angles

I am asking a related question here : Newton's Third Law Angular Bouncing Why, given newton's third law would a ball bounce at an opposite angle to it's original, if an equal and opposite force ...
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1answer
21 views

Newton's Third Law Angular Bouncing [duplicate]

I am asking a related question here: Newton's Third Law Opposite Angles If a ball is accelerating at a surface at a non-straight angle, it will bounce off with the opposite trajectory, like if ...
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3answers
157 views

What is the significance of clamping the center of the spring?

7. A block is hung on a spring, and the frequency $f$ of the oscillation of the system is measured. The block, a second identical block, and the spring are carried in the Space Shuttle to space. ...
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6answers
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Why is kinetic energy stored as potential energy in a body during its motion against gravity?

Everyone knows kinetic energy is converted to potential energy in the body when it moves up against the earth's opposing gravitational force. But I am facing some problem with this. What I learnt ...
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0answers
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Best book for studying Newton's laws, conservation of momentum, etc [duplicate]

Best book for studying Newton's laws, conservation of momentum, etc, so that I can apply these laws anywhere. (I want to analyze fluids on my own.) I have studied bernoulli and Euler etc those ...
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1answer
92 views

Case of the mysterious bullets (taken from Mad About Physics)

"Two ideal bullets, identical in shape, size and mass, strike the same target with the same speed just before the collision. Force meters at the target register two times the force value for bullet A ...
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2answers
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Effect of movements of astronauts on International Space Station

I know that astronauts move in and around in ISS. When they move they also touch the modules of ISS and sometimes they apply force on the module to move. When this happens, as far as I know it affects ...
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1answer
68 views

Center of mass after explosion [closed]

How he treated the center of mass as if it is still in the same place , is not it supposed to change after explosion ? and is not explosion destroying the closed system? i mean it represents and ...
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2answers
79 views

Space Elevator: how would you keep the end of a Space Elevator's cable rigid?

I had a discussion with my wife about physics behind a Space Elevator. Imagine a cable rising 60k into the firmament for its elevator to climb. The cable would have to rotate in unison with the earth, ...
2
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1answer
95 views

Rolling a ball into a cone; what should the forces overall be?

This is my solution to finding angular displacement/velocity/acceleration on cone so far. Consider a cone, with an apex of half-angle $\psi$ pointing down, and a height of $h$. If I roll a ball into ...
2
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1answer
107 views

How did Newton establish his famous third law of motion?

For every action,there is equal and opposite reaction . This is the famous Newton's third law of motion. But how did he come to this conclusion? We can prove 2nd law using calculus. But how did Newton ...
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1answer
53 views

Non-deterministic particle system

This question is in the spirit of Norton's dome, an example of an apparently non-deterministic system in Newtonian mechanics. Under certain restrictions, the Picard–Lindelöf theorem guarantees the ...
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0answers
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Plank stopping time (Continuation and Physical meaning)

A while back I asked this problem: "Plank stopping time" I thought it was solved, but now I have some questions about the solution. Problem: A plank of length $L$ and mass $m$ lies on a ...
1
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1answer
56 views

Simple Harmonic Motion homework [closed]

Suppose we have a rod of mass $m$ and length $l$ which is pivoted at center and two springs of spring constant $k$ are attached at opposite ends so that it performs simple Harmonic motion when ...
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0answers
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Tension in a pulley system [closed]

In the question above, what I don't understand is how to calculate the tension in the second case (case in which the pulley is there). I realized after reading some questions, that the arrangement ...