# 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.

11,193 questions
27 views

### 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 ...
287 views

### 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: ...
50 views

### 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 ...
28 views

### 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 ...
45 views

### 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. ...
61 views

### 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 ...
42 views

### 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 ...
44 views

### 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 ...
28 views

### 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 ...
24 views

### 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 ...
23 views

### 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 ...
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 ...
65 views

### 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 ...
8k views

### 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 ...
34 views

### 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 ...
33 views

### 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 ...
17 views

### 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. ...
32 views

### 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? ...
63 views

### 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?
13 views

### 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 ...
6k views

### 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?
28 views

### Why is instantaneous velocity of particle on circular disc perpendicular to position vector taking point of contact as origin during rolling motion

Why is P0P2 perpendicular to velocity vector $\vec{v}_2$ in the diagram?
24 views

### 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, ...
32 views

### 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 ...
24 views

### 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\...
74 views

### 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 ...
49 views

### 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?
24 views

### 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. ...
28 views

### 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 ...
78 views

### 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, ...
33 views

### 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 ...
31 views

### Force due to change in energy

We know change in kinetic energy is equal to total work done by all the forces acting on the object.For work done there should be a force .What's that force.direction? ex a parallel plate capicitor's ...
76 views

### $\Delta K=\Delta U$ vs $\Delta K = -\Delta U$

While doing physics homework, I noticed that in some problems, the change in kinetic energy(KE) is equal to the change in potential energy(PE), even though I learned that conservation of energy shows ...
63 views

### Is Verlet method suitable for to solve projectile motion with quadratic drag?

Consider the following non-dimensional equations of projectile motion in presence of air resistance, I understand it can be numerically solved using the mid-point method, but can I also use Verlet ...
27 views

### Tension in a string attached to a spring with deformation at a point

I am trying to calculate the tension in a string in the configuration shown in the diagram below. Here is a verbal description of the setup: The string is fixed at one end with the other end connected ...
68 views

### Projectile with air resistance from a given hight

Objects take same time to fall a given height independent of their horizontal speed when air resistance is ignored, is this also true when air resistance is not ignored? In presence of air resistance, ...
78 views

### Why don't objects bounce infinitely?

I'm computer programmer, and I was making a little test of my “possibilities”, so to speak, so I made a small game with sort of gravity, bouncing ball and walls around. Recently I've noticed that ...
31 views

### Finding force on an object from newton's second law of motion

Imagine a body of mass "m" inside a box of mass "M".Let us assume that box is moving at a constant velocity.Then an observer from outside would see both the body and box moving. Let us now apply a ...
44 views

### Where does 4N and 3N goes in this diagram?

Two forces of 3 N and 4 N are acting at a point such that the angle between them is 60 degrees. Find the resultant force. I successfully draw diagram for above sentence: But I am confused which one ...
31 views

60 views

### How are objects able to move even after newton's third law of motion [duplicate]

I can't understand at all why objects move even though after newton's third law.I also have a doubt in following example If we apply a force on an object the object applies a backward push on us ...
21 views

### Is it possible to find the linear and angular forces?

Suppose an object has both linear an angular motion. Let's consider the object a sphere. What we know: - The angular velocity and acceleration - The linear acceleration of the center of mass. - The ...
40 views

### Weighing machine, kg vs. N

When I stand on a weighing machine and it shows me the number 75 , is it my mass in Kg or the Normal Force due to gravity in N
36 views

### Would conservation of angular momentum make it difficult to fall sideways in an O'Neill space colony?

It's always bothered me that the O'Neill space wheel puts forth centrifugal force as a suitable replacement for gravity. However, it seems the effects of conservation of angular momentum would induce ...
14 views

### Overspeed Trip Valve Design

I want to estimate impact force generated due to collision between rotating body and stationary object. Bolt assembly is in balanced condition with the spring force and centrifugal force. As the speed ...