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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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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?

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 write it simpler 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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2answers
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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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1answer
39 views

Force Distribute of a Draped chain

Imagine that there is a chain that is (L) meter in length, uniformly weighted along its entire length at (x) kg/meter. The two termination (A and B) are displaced in both a horizontal axis by (y) ...
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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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Dynamics collisions - reduced mass

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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Making FBD in Newtonian dynamics [on hold]

Can anyone give me a general method to make free body diagrams with strings and springs in Newtonian Dynamics that would help me to solve Physics Olympiad questions easily??(Without using analytical ...
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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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1answer
41 views

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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1answer
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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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1answer
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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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2answers
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Why do we differentiate displacement to get velocity if displacement is given as a function of time [on hold]

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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1answer
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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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1answer
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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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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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Momentum and impulse [on hold]

Your mass is 60.6kg and you are about to land on your feet after a jump, falling at 0.85m/s . Calculate the average force acting on each foot if: you keep your knees locked and stop in 0.082s .
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Inertia tensor of cube with varying density [on hold]

We have a loaded die shaped like a cube of length $2L$. The density varies with the density function $p(z) = p \left( 1 + \frac{z}{2L}\right)$ The center of mass is $(0,0, \frac{L}{6})$. Calculate ...
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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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Related to the information contained in $a = v \frac {dv}{ds}$

While studying kinematics I came to the definition of acceleration which is $a = \frac {dv}{dt}$. But from this equation we can derive that $ a = v \frac {dv}{ds} $ which when I evaluate at $v=0ms^{-1}...
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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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Collisions and Friction [on hold]

A ball is tossed from top of a tower 10m high, with velocity 10m/s, at an angle 30° with the horizontal(anti clockwise) at t=0, on a plank of same mass and negligible thickness lying on the ground. ...
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4answers
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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

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
65 views

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 ...
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Total extension in spring

A block of mass 200g is suspended through a vertical spring. The spring is stretched by 1cm when the block is in equilibrium. A particle of mass 120g is dropped on the block from a height of 45cm. The ...
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1answer
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Can a longer jumper out jump its own running speed? [on hold]

I would like to know if a long jumper can out jump its own running speed of let's say 8 meters? If he were to take off and jump would that increase its horizontal speed in the air so much more that ...
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1answer
26 views

Which approach to take with a vertical spring?

Lets say we have a spring hanging vertically with spring constant $k$ attached to a block of mass $m$. The system is at rest. Then, you pull the mass downwards, extending the spring by distance $x$,...
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Help on a problem [on hold]

So I have a problem. It goes as follows: A car is driven down at a constant speed of 76 km/h down a road. The engine delivers 48 kW of power. Calculate the average force that is resisting the ...
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2answers
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Newton's 3rd law in lami's theorem

I'm a high school physics student dealing with the following problem: Despite solving the problem correctly, I don't understand the diagram (b) supplied with the problem: These are my questions: ...
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3answers
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What is torque, really? and can it be determined for a point on a circle that is away from the center of the rotation axis by a radius $r$?

Let's picture a Rolling without slipping Wheel, that constantly accelerates. radius of a wheel/circle is $r$. Basically any wheel of a vehicle is rotating around its fixed axis - AoR -(axis of ...
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Friction: Rolling Motion [on hold]

If a body rolls down an inclined plane and then moves up another frictionless inclined plane, then the height from which it rolled down will be more than or less the height it moved up on frictionless ...
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1answer
56 views

Distance traveled by a particle in $n^{th}$ second

My book states that the distance traveled by a particle thrown upward in the last second is independent of it's initial velocity because the the object travels the same distance as a freely falling ...
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2answers
51 views

Understanding newtonian gravity

In gravitation that two object mutually attract applying equal forces on each other. But for instance if we take a disc and a solid sphere the fact that they have different gravitational fields on on ...
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2answers
42 views

Is projectile angle for farthest distance same for human arm?

A projectile, in other words, travels the farthest when it is launched at an angle of 45 degrees. But human arm's velocity may vary at different angle, so angle for farthest distance may not be 45°.
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Calculating Mass of a block in this pulley block systen

This question was asked in My Viva- Consider this pulley block system.This system is equilibrium in equilibrium . Now assuming string to be non elastic this would imply M1= M2 (as tension is uniform ...
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2answers
172 views

Why do we feel weightlessness during free fall?

An object in free fall accelerates towards the Earth at a acceleration equal to $g$ (the accleration due to gravity). Now if we ignore the air resistance, why do we feel weightlessness? I could not ...