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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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Why does a helium balloon rise? [duplicate]

This may be silly question, but why does a helium ballon rise? I know it rises because helium is less dense than air. But what about the material of the ballon. It is made up of rubber/latex which is ...
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1answer
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Can a syringe be used as a hanging scale if needed?

FYI: This is not a homework q; I am just curious... You can assume that... the syringe tip cap creates a "perfect" seal, i.e., keeps air from flowing in/out! the syringe is completely depressed ...
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Kinetic energy of an object

We know that motion is relative. So let an object(o) be moving with a certain velocity with respect to an object (A).If another object (B) is moving with respect to (A) at a given moment and they ...
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What causes the mass connected to the end of a pendulum to speed up when its pivot is moved?

Consider a pendulum with a massless and unstretchable string connected to mass M on one end, and to a moveable pivot on the other end. We assume this is on Earth, so gravity acts on the mass. We also ...
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Work done by a weight lifter

The following problem is from "The Physics Classroom": Lamar raises a loaded barbell from the floor to a position above his head with outstretched arms. Determine the work done by Lamar in lifting $...
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Did the plane use the mechanical advantage of the inclined plane to fly into the sky? [duplicate]

The wing is an inclined plane, and the inclined plane has mechanical advantage, so the aircraft can fly up to the sky with less force than the weight of the aircraft?
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7answers
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Initial speed is zero and so is power?

If I want to accelerate something from standstill to max speed, with a constant force (acceleration and mass don't change), the equation P = F * v would say that in the beginning we use 0 W power. How ...
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3answers
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What is the net force on an object which is moving with a constant velocity? [closed]

Imagine a toy car moving with a constant velocity. By Newton's second law of motion we can see that $F=ma$ and, since there is no acceleration, the net force is zero. But still we can experience a ...
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2answers
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Why does Friction act Parallel to the Surface (Microscopic Level)?

If we assume an object (blue layer) sliding towards the right across a surface (black layer). According to Newton's 3rd Law, the frictional force would act to the left (resisting the object's relative ...
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0answers
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Vertically falling sphere striking a wedge and rolling without slipping

I have a question which states that a sphere of mass $m$ falls vertically and strikes a wedge of mass $M$ and inclination $\alpha$, at rest on a smooth horizontal plane. There is sufficient friction ...
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7answers
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Why electric potential requires absence of acceleration?

As of 28/05/2019, Electric Potential is defined in Wikipedia in the article with the same name as: The amount of work needed to move a unit of positive charge from a reference point to a specific ...
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5answers
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Why the work done by system not stored as potential energy?

Now choose a spring mass system now work done by external agent in slowly moving from equilibrium position is stored as potential energy but where is work done by spring force gone.For genralization ...
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String conservation with springs

I was trying to solve this Problem that asked to find the period of small oscillations for this system. To do so I used the fact that for a massless pulley with strings around it, the sum of the ...
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1answer
42 views

Non-integrable differential equation and non-holonomic contraints

From the constraint $v=a\dot{\phi}$ of a rolling disk over a plane, where $a$ is the radius of the disk we can derive these two equations: we have two differential equations of constraint: $dx=asin\...
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0answers
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Holonomic constraints and variables

Let's consider a holonomic constraint: $$f(q_{1},...,q_{n},t)=0$$ Must every term that compares in the equation be writable as a combination of the variables of a function? For example, in the ...
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0answers
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Why does increasing the length of suspension strings increases a bifialr pendulum period of oscillation?

Given where L stands for the length of suspension springs. What is the physics behind the correlation between the period of a bifilar pendulum and the length of its suspension strings?
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1answer
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Polar form of Newton's Second Law

Can someone please show the steps for deriving the total energy of a particle from the Polar form of Newton's Second Law?
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2answers
38 views

Steady velocity forces

When an object is moving at constant "steady" velocity, the resultant force is equal zero. But I can not understand how the object moves and at the same time, backwards and forwards forces are the ...
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0answers
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Tension - Normal Reaction dilemma

A hemisphere of radius 'R' is kept on a horizontal surface. A nail is also fixed at 'O' exactly above centre of hemisphere at some height. A small ball of mass 'm' is slowly pulled by an external ...
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0answers
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Newton's second law in angular form

I'm rather confused about the correct form of Newton's second law in angular form and how matrices of inertia could be converted from one coordinate system to the other. Consider the system below: ...
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3answers
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Sphere and Bar freefall [closed]

Question The problem consists of a bar of weight $W$ to which a sphere of also of weight $W$ is fitted at one end. The conbination is released from rest, with the bar horizontal. How will the ...
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1answer
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How does the following variables affects the period of a bifilar pendulum?

Hey everyone, I am a highschool student from New Zealand and I have 4 questions concerning the period of a bifilar pendulum system. It is very much appreciated if you can answer in detailed ...
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Newton vs. Einstein in universe evolution description

The equation for the universe evolution in the presence of a perfect homogeneous fluid, namely $$\dot{R}^2+k=\frac{8\pi G}{3}\rho R^2$$ can be obtained by solving Einstein equation with some effort. ...
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1answer
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Trouble with grasping D'Alembert's Principle intuitively

In Newtonian mechanics we all learned that a mass accelerates when it is under the influence of a nonzero net force. However, I learned of D'Alembert's Principle today and it seems to oppose what I ...
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1answer
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Contradiction between conservation of momentum and conservation of energy [closed]

Let's say that a $2\text{ kg}$ cart is rolling (frictionless) along a surface at $2\text{ ms}^{-1}$. A suspended $2\text{ kg}$ weight is then dropped onto it from above. If we apply the law of ...
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1answer
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Deriving equation for $\theta$ [closed]

I have that the energy $E$ in a system is $$E = \frac{1}{2}L^2\dot{\theta}^2(m_1+4m_2) - Lg(m_1+2m_2)cos(\theta) + c$$ where $c\in\mathbb{R}$. I have used the conservation of energy over time to ...
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Sling loads for multipoint lifts

I am trying to calculate sling loads for a n-point lift. I want to utilize vector calculations and make it as general as possible, and also work in 3D-space. The idea is to use position vectors for ...
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1answer
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Understanding the potential energy of the Atwood machine

So this might be a pretty simple (dumb?) question. I don't understand the choice of the potential energy on this problem. I really can't see how the "height" in the potential energy of the masses is ...
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0answers
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When a 1D linear object is squeezed along this straight line, does it break and become 2D?

There is a straight wire that has minimum thickness (thus I say it's one-dimensional). If you squeeze this straight wire from its two end, and the forces are strictly along this straight line (like in ...
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1answer
51 views

Is this terminal velocity figure reasonable? [closed]

I used an online calculator to find the terminal velocity of a phone falling sideways assuming it to be an aerofoil. is the value of 7500 m/s reasonable?
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1answer
26 views

Prove acceleration in orbit with newtons second law

I want to prove that the acceleration in a orbit at a given point r=(x,y) is $a=-\frac{GM}{R^3}r$ (My professor said this can be proven by newtons second law, but he never explained in detail how). I ...
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4answers
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What is the correct formula for relative velocity?

I have consulted byjus.com, HC Verma and Khan academy, all are saying different. byjus and HC Verma book is saying that formula for relative velocity is $V_a +V_b$ but in Khan academy they are telling ...
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5answers
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Is floating in space similar to falling under gravity?

In the case there is no air and your eye are closed, then does falling from the sky under gravity have the same feeling as floating in space? Can our body feel that we are accelerating without the ...
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2answers
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Does air resistance have a greater affect on longer pendulums than shorter ones due to the greater exposure it has to air?

I'm thinking, because longer pendulums travel for a greater time period through the medium of air, air resistance will have a greater affect on the pendulum bob (and string) and so the angle the ...
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2answers
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Increasing Mass VS Increasing Force when pushing a Box [closed]

If we assume g=10m/s^2 & negligible friction The force needed to accelerate that box by 5m/s^2 would be 500N. This is a very basic one. The confusion came when an force of 250N (the force a 25kg ...
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2answers
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Conservation of Angular Momentum w.r.t a Reference point

When angular momentum is conserved, does it mean that it does not matter what the reference point is at? Say for example with this image below, the observer stands at two possible points P1 and P2. ...
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1answer
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Work-Kinetic energy theorem derivation

So I came across this derivation in the book Classical Mechanics by Herbert Goldstein. I don't follow from the second step onwards. I understand that there's a dot product, but how do you compute it? ...
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2answers
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Conservation of energy when slowing an object down

If it takes energy to slow an object down, and then the object also loses KE, then how is energy conserved? Don't you have a net loss of energy?
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0answers
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How to calculate acceleration in this Atwood's Machine?

Question: https://i.stack.imgur.com/xYp18.jpg It asks us to find the acceleration of block B. Attempt: I concluded the net force on block B would be (300-3T) where T is the tension in the string ...
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7answers
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Why doesn't the Earth's acceleration towards the Moon accumulate to create noticeable motion of the earth, towards the moon

I get that Earth's mass is very large, so its acceleration is very tiny. But wouldn't the acceleration accumulate over a period of time and become noticeable?
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0answers
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Approximating the orbit of an object tied to another by a rope which is shortening

Working off my previous question, I think I've finally managed to describe what I'm wondering about in a quite clear, non-vague way. Suppose we have an object $B$ tied to an object $A$ by a rope, ...
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2answers
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How is it possible for a meta material to turn a push into a pull? Wouldn't that violate conservation of momentum?

This article: https://www.sciencedaily.com/releases/2019/05/190524140857.htm seemed fine until I hit this quote: "If you were wearing a football helmet made of this material and something hit the ...
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1answer
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Electron equations of motion for plasma

I'm reading through an Introduction to Plasma Physics by Francis F. Chen, and in the simplified derivation for plasma oscillation in 1D, the book quotes the electron equations of motion as: $$mn_e\...
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1answer
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Distance from ground to start suicide burn with initial height [closed]

In the figure below, the rocket is dropped with no initial velocity at a height of $h$. $d_f$ (free fall distance) is the distance in which the rocket is in free fall. $v_b$ is the velocity due to ...
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1answer
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How do conservative forces conserve mechanical energy?

A force that conserves mechanical energy is known as a conservative force. Question: How do conservative forces conserve mechanical energy?
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1answer
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Change of orbit with tangential impulse

I see a similar question: Change of orbit with a radial impulse. The answer to that question seems fine to me. In the answer, mention is made of this similar question, but it is not fully treated. ...
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0answers
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Movement of an object tied to another

Suppose we have two objects $A$ and $B$, where $B$ is tied by a rope to $A$ with the slack pulled out, the initial tangential speed $c'(0)=(0,1)$ is perpendicular to $c(0)$ and $c(0) = (1,0)$, and ...
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2answers
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Throw a ball AT a moving train, in what direction does it reflect?

You are standing at a platform, with a ball. a train approaches and u throw the ball at it in a straight line from a small distance. in what direction des the ball reflect off? heres what i think, ...
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1answer
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Some questions concerning orbits of objects [closed]

I've been playing around with some physics problems and trying to figure out things by myself, mostly just for fun. I would appreciate if someone corrected my thoughts and gave me some feedback. I'm ...