Questions tagged [newtonian-mechanics]

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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Releasing items in the hold of a ship makes it easier to rock a ship?

There's a scene in the movie Pirates of the Caribbean III (At World's End) wherein the characters are trying to flip their pirate ship upside down as it floats in the water. To do this, they try to ...
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How is power of engine transferred to kinetic energy of car?

Okay, I understand that via the torque from the engine, the wheels push back on the ground, and static friction pushes forward, thus accelerating the car. However, the force of static friction does ...
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Why does the action $S=\int L dt=\int (T-V) dt$ have to be minimised (or maximised) to produce Newton's Second Law? [duplicate]

We have recently covered the Lagrangian in our lectures, whereby it was shown that all equations of motion ($x(t)$) satisfying the Euler-Lagrange equation with Lagrangian $L=T-V$, where $T=\frac{1}{2}...
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Deformation of an elastic ball

Suppose a sponge ball is being compressed, due to applying a known force in a specific direction. The ball's shape will be distorted. Given that the deformation (displacement) is known in the ...
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moment of inertia for 2 point masses

I don't really get why this equation is true, it's the equation for the moment of inertia of 2 point masses with $r= r_1 + r_2$. I know how we come to the first equation, but not how we come to the ...
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On methods to know the type of friction

Suppose 3 blocks are stacked on top of one another and a constant force is applied on the bottom one, how could I know if the friction that is acting on those objects is kinetic or static? Moreover, ...
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Is work-energy theorem valid in non-inertial frames?

From this answer for the question Is the energy conserved in a moving frame of reference?, I learnt that the work-energy theorem is independent of the frame of reference. But, is the theorem valid ...
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Can the work by static friction on an object be negative?

We know that static friction acts between two surfaces in contact when they are not moving relative to each other (and when some other force is trying to move one object over the other). This question ...
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1answer
53 views

On the rotation of an object accelerated by gravity with a moving base [closed]

How could you describe the rotation/falling of an irregular object whose base/rotational point is being moved with constant acceleration to the left? How much will the angle between itself and the ...
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1answer
26 views

Mechanical advantage

Would the mechanical advantage or behavior of a second class lever change if the load was "bolted" underneath the lever arm as opposed to the classical diagram of the load resting on top? I'm just ...
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Why doesn't the block fall?

I came upon this question as I was going through the concepts of tension. Well according to Newton's third law- every action has an equal and opposite reaction. Here my question is that if the tension ...
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1answer
36 views

Limits of analysis in ideal mechanics questions

DIAGRAM This is the diagram given in a question which I am solving now.Just to mention this isn't a homework question because I think I have actually got a doubt.Normally I use virtual work method to ...
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4answers
69 views

Can the work by kinetic friction on an object be zero?

We know that friction is of two types - static and kinetic. Static friction acts when there is no relative motion between the surfaces in contact. Kinetic friction takes place when surfaces rub ...
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Projectile motion: variation of the equation of the trajectory and motion introducing air resistance

In this site I have seen several questions/answer of the projectile motion. For example very close question/answer is into this link: Add air resistance to projectile motion My students of an high ...
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1answer
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Frictional force acting on an object being lifted from ground

I believe that when we lift an object placed on a rough surface then initially frictional force(due to the cold welding) acts on the object (together with gravitational force) to oppose the relative ...
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Analysis of gravitational interaction between small discrete particles forming a spherical cloud

Imagine a huge number of small discrete particles forming a spherical cloud. My assumptions:- They are stationary at $t=0$. The particles are isolated, i.e. there is no external influence due to any ...
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Rigorous proof of Bertrand's Theorem for orbits under central force

I have read through several proofs of Bertrand's Theorem, including the one on Wikipedia. A typical proof can be found here (Santa Cruz Institute for Particle Physics). Almost all proofs using ...
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Expectation value of Sz operator on the 0 Eigenstate in Spin 1 system

I'm trying to evaluate for the expectation value of the $\hat{S}_z$ operator on the $|0>_z$ eigenstate, which I'm assuming can be expressed $<\hat{S}>=<0|\hat{S}|0>$. I know the general ...
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Position vector of an eccentric binary

For a circular, equatorial ($z=0$) Newtonian binary, the position can be clearly written as, $$ x_i = r(\cos \Omega t, \sin \Omega t, 0)$$ for orbital frequency $\Omega$. My question is how would ...
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How are the Euler-Lagrange Equations any more coordinate-invariant than Newton's?

In my experience it is often said that the Lagrangian formulation of mechanics can be much much more convenient because the form of the (E-L) equations remains the same whatever coordinates we choose, ...
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2D collision of round objects; Is this correct? [closed]

I'm creating a collision simulator for round objects. I've written out the physics and I just wanted to ask if it's correct. Are there any parts I should change, or any way to simplify it more than ...
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4answers
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Is there a displacement at all when the resultant force equals zero and the body is at rest?

Force is the change of momentum in time. But suppose a body is at rest on the floor. The system is in mechanical equilibrium, meaning that the forces acting on it sum up to zero and there is no ...
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Work Done by a Car Pulling a Sled

Is work still equal to force times distance if there is no acceleration? Consider an electric car pulling a sled at a constant velocity as shown. The static friction force $F$ at the wheels is equal ...
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Should the coin be heavier or lighter in the coin drop experiment?

The Coin Drop experiment is a classic experiment used to demonstrate Newton's First Law of Motion. In this experiment, a glass is covered with a card and a coin is place on the card. The card is given ...
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Why does the derivative become $x=r\dot\theta\cos(\theta)$ when calculating angular velocity?

This is not a homework question because I do not want help with solving my homework. I would rather want an explanation of why the derivative of this seems to break math as I know it. Background ...
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Why does water flow downhill?

Researching this topic, I found everyone just saying because of gravity. But that makes no sense to me. Gravity exerts a downward force: But water flowing downhill goes sideways. There must be a ...
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Elastic Collisions - Equation not working?

This is the question: When cars are equipped with flexible bumpers, they will bounce off each other during low-speed collisions, thus causing less damage. In one such accident, a 1850 kg car ...
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3answers
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Centripetal and Centrifugal acceleration/force [duplicate]

Centripetal force acts towards the centre and necessary to keep an object in circular motion. But centrifugal force is equal to the magnitude of centripetal force and acts in outwards direction and ...
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1answer
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Dynamics collisions - reduced mass [duplicate]

In dynamics when doing collisions from the centre of masses' frame of reference we use reduced mass. What is is it and why do we use it?
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Why are gravitational mass equal to the mass in Newton's second law [duplicate]

Newtons second involves the mass $m$ e.g. $$ F = m a $$ And the gravitation force also involves the mass e.g. $$ F = - G \frac{m_1 m_2}{r^2} $$ The question is why the gravitation mass is equal to ...
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Conservation of energy when ball rebounds

Consider a ball that strikes a stationary box and has momentum $mv$. If the ball rebounds with the same speed it had before the collision, its momentum is $-mv$. Therefore, the box must have a ...
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Is Newton’s gravitation law able to explain the circular motion of the earth around the sun?

I have read in Forbes website that the orbit of the earth around the sun is expanding (by 1.5 cm in 2019). I have also heard that big bang theory suggests that the universe would collapse into ...
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Mean free path equation derivation

I was reading about mean free path equation derivation online and stumbled upon this: We will derive the equation using the following assumptions, let’s assume that the molecule is spherical, and ...
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Is Newton's first law an “If and only if”

On Wikipedia, Newton's first law is stated as: In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force. I read ...
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Does universal proof exist for newton's experimental law for all cases of elastic collisions?

Newtons experimental law I. E velocity of approach is equal to velocity of separation (for the points on the two bodies where the collision takes place) for an elastic collision is applicable for ...
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Tension at lowest point: oberbeck pendulum

I'm solving a problem involving oberbeck pendulum We are given $M$, $m$, $r$ (radius of pulley), $R$ (distance from center of rotation to each of the 4 small weights). The problem says that the ...
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Nobel Prize in Physics 2019 on exoplanets and Hot Jupiters

The 51 Pegasi b, discovered by Didier Queloz and Michel Mayor is classified as a hot Jupiter and not considered to be a star. I had read a bit about the minimum mass necessary for being a brown dwarf ...
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Why do we differentiate displacement to get velocity if displacement is given as a function of time [closed]

Like if the displacement is given as S=(2t³)and if we are asked to find the velocity in 2 seconds then if we put t=2 in the expression we get 16 which isn't correct. The correct must be dS/dt=6t² and ...
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Is it normal to assume equal impact time?

If we have two hammers of different weights both hitting an object with the same force can we assume they both have the same impact time?
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Objects slowing down

I know that when an object is moving on a suface it slows down due to friction , now since the kinetic friction on the object is constant (and it's the net force on the object since the normal force ...
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2answers
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Which road will have less wear and tear of tires, a concreted or a tarred road?

I am wondering that where could be more friction, whether on a concreted road or tarred roads. My question is that which road will have less wear and tear of tires, the concreted or the tarred roads?
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Advisory speed limits on turns

I was just thinking about why many corners have advisory speed limits that are less than the highway speed limit, does it have to do with centripetal acceleration?
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Understanding Vis-Viva equation

I have seen two different forms of the vis-viva equation: \begin{align} v^2 &= GM\left( \frac{2}{r} - \frac{1}{a} \right) \tag{1} \\ v^2 &= G(M+m)\left( \frac{2}{r} - \frac{1}{a} \right). \...
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Circular motion and banked roads question

I can't work out c) for the following question, and I'd just like some help clarifying why my solution is wrong. Part a) and b) are fine. A car rounds a bend on a road that follows the arc of a ...
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On understanding the relation between Heisenberg Uncertanity Principle, Indeterminism and classical chaos

I recently read Emperor's New Mind by Roger Penrose. In it he talks at length on the notion of determinism in science. In this context how does the Heisenberg Uncertanity Principle bring about the ...
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Friction on Parallelepiped

Is the friction on a parallelepiped with mass m equal to the friction on a dice with the same mass? Because the overhang of the parallelepiped causes an irregular distribution of the normal force on ...
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2answers
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Role of friction during Collisions

Normally, in questions of collisions, we tend to apply conservation of momentum (and in cases of elastic collisions, conservation of energy as well) and we usually ignore the frictional force acting. ...
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Acceleration-time graph for a falling object

I understand that when drawing an acceleration-time graph for a falling object (with initial velocity = 0), the y-intercept should be $9.81ms^{-2}$ and acceleration should end up being $0ms^{-2}$ as ...
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2answers
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Question on flywheels and angular momentum [closed]

I've recently been exposed to gyroscopes in my physics class. We discussed flywheels in relation to the gyroscopic effect. I was wondering how the stationary flywheel scenario worked. Why is it that ...
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3answers
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Electron volt $eV$?

$1 eV$ is defined as the energy gained by an electron when accelerated through a potential difference of $1V$. But, I think when the electron is accelerated, it gets closer and closer to the source of ...