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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108 views
How to reconcile the two definitions of work? (mechanical and thermodynamical)
When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$.
However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$.
I'm having trouble ...
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vote
2answers
189 views
Preventing a block from sliding on a plane (with friction)
Assume a small square block $m$ is sitting on a larger wedge-shaped block of mass $M$ at an upper angle $\theta$ such that the little block will slide on the big block if both are started from rest ...
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1answer
129 views
Spring Constant
Is it possible to determine the spring constant of a spring in a situation in which it is being compressed when such certain length of compression is not known? If so, how can such calculation be ...
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0answers
29 views
Find amount of force to move a 18 kg mass 0.1 seconds [closed]
Force is coming from two pistons pushing at 45 degrees applied to two adjacent corners of a square (0.6 m x 0.6 m) rigid plane. Mass of the plane is 18 kg. Piston stroke is 20 cm, piston bore is 40 ...
-1
votes
1answer
62 views
Rotation System Dynamics - Unit conversion issues [closed]
I'm having issues with unit conversions when for rotational systems. All of my components (spring, mass, damper) come in Imperial units, so I did all my calculations in Imperial. When I convert to ...
2
votes
2answers
33 views
Velocity in a turning reference frame
I often see the relation that $\vec v=\vec v_0+ \vec \omega \times \vec r$ in a turning reference frame, but where does it actually come from and how do I arrive at the acceleration being $$\vec ...
-1
votes
1answer
100 views
Newtons Cannon ball problem [closed]
Let's I have a Newton's Cannon ball of 15 kg and want to fire so it will round the earth and back to me.
My query is which law can evaluate the speed that cannon ball will revolve round the sun ...
5
votes
3answers
118 views
Moment of Inertia (triangular plate)
I want to generalize the formula for the MOI of a triangular plate (sides $a,b,c$) about an axis passing through mid point of one sides and perpendicular to it's plane .
The mass of plate $M$ is ...
2
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1answer
70 views
Understanding Kepler's problem
I wanted to know a few things about elliptical motion, that I do not understand so far.
Let's imagine that we have an attractive gravitational two body problem where both bodies carry out elliptical ...
7
votes
2answers
170 views
No closed orbits for a Newtonian gravitational field in 4 spatial dimensions
We are supposed to show that orbits in 4D are not closed.
Therefore I derived a Lagrangian in hyperspherical coordinates
$$L=\frac{m}{2}(\dot{r}^2+\sin^2(\gamma)(\sin^2(\theta)r^2 \dot{\phi}^2+r^2 ...
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0answers
18 views
Stability of trajectory of disc which moves along a straight curve
Let's have a disc which moves along a straight curve on a plane in a uniform gravitational field. There need to discover the stability of it's trajectory.
I represented the possible deviation of the ...
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2answers
118 views
A small oscillations of a rod on the cylinder
Let's have the next case.
A rod (with mass $m$, length $L$ and a momentum of inertia $I$) at the initial time is located on a cylinder (with radius $R$) surface so that it's (rod's) center of mass ...
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3answers
180 views
The impossible possibility - weightless mass
I have a hypothetical question about inertia.
Let's say I have an object with inertial mass a ton (2,000 lbs.), and it is sitting in my front yard, for instance. If it would suddenly become immune ...
8
votes
2answers
290 views
Is acceleration an average?
Background
I'm new to physics and math. I stopped studying both of them in high-school, and I wish I hadn't. I'm pursuing study in both topics for personal interest. Today, I'm learning about ...
5
votes
1answer
87 views
What if the lid of a pressure cooker was suddenly released?
My dad and I have tried to calculate the strength of the explosion if the lid was suddenly freed. We took some measures:
Lid mass: $0.7 \textrm{kg}$
Lid surface: $0.415 \textrm{m}^2$
Internal ...
0
votes
3answers
49 views
Forces involved in a climbing jet aircraft
I have a problem with which I need help. The question is:
A jet aircraft is climbing at an angle of 45° above the horizontal and is accelerating at 4.5m/s2. What is the total force that the cockpit ...
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votes
1answer
46 views
Simple pendulum and planet mass [closed]
A simple pendulum, $20cm$ in length, has the period of $2.7s$ on a certain planet. Find the mass of the planet if its diameter is $18000km$. $G=6.67\times10^{-11}Nm^2/kg^2 $
I have no idea how to get ...
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votes
3answers
1k views
Galilean invariance of Lagrangian for non-relativistic free point particle?
In QFT, the Lagrangian density is explicitly constructed to be Lorentz-invariant from the beginning. However the Lagrangian
$$L = \frac{1}{2} mv^2$$
for a non-relativistic free point particle is ...
24
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5answers
2k views
With Newton's third law, why are things capable of moving?
I've got a rather humiliating question considering newton's third law
"If an object A exterts a force on object B, then object B exerts an equal but opposite force on object A" -> $F_1=-F_2$
...
1
vote
2answers
66 views
Velocity of an object undergoing homogenous acceleration
So I was considering the following problem within the context of Special Relativity:
Given an object O, with initial velocity v, undergoing constant acceleration at a rate of a, I want to express the ...
25
votes
10answers
6k views
How did Newton discover his second law?
I've always assumed/been told that Newton's 2nd law is an empirical law — it must be discovered by experiment. If this is the case, what experiments did Newton do to discover this? Is it related to ...
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1answer
54 views
Bouncing ball simulation computer science
In my Computer science class I was given a problem where I have to simulate a bouncing ball using "real physics". I have been trying to find a equation that will simulate the height of the bounce ...
3
votes
1answer
200 views
Firing machine question
Suppose we have a firing machine on a frictionless surface at point $x=0$. It fires a bullet of mass $m$ every $T$ seconds. Each bullet has the same constant velocity $v_0$. There's a body of mass ...
3
votes
2answers
171 views
Nonuniform acceleration due to rubber rope
What I want:
I have a rubber rope which is $5m$ in length when not stressed and is able to stretch about $100\%$ (to $10m$ long). I want to accelerate a constant mass horizontally, which has ...
3
votes
1answer
31 views
Two masses on rope spinning around
Two balls of the same mass $m$ are connected to each other with rope
of length $l$. One of the balls is also connected to the ceiling with
a rope of the same length $l$. The balls are spinning ...
44
votes
8answers
5k views
Proof that the Earth rotates?
What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis?
By basic physics I mean the physics that the early physicists must've used to ...
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votes
2answers
81 views
acceleration due to gravity [closed]
From the picture we can evaluate the vertical and horizontal component:
Given on a book:
The figure above shows a small mass connected to a string, which is attached to a vertical post. If the ...
4
votes
2answers
105 views
Thrust center in space
I have this dilemma: Suppose you have a space ship somewhere in deep space, where there is no drag force or substantial gravity. If the ship has a single engine situated in such a way that the center ...
3
votes
1answer
74 views
Oberth Effect in deep space
Does the Oberth effect only apply when in orbit of a planet or would a rocket generate more and more thrust (if kept on) even in deep space?
Wikipedia explains that the faster the rocket goes, the ...
2
votes
3answers
99 views
How you feel in outer space vs. orbit?
I understand that when someone is in low earth orbit, the "pull" of their inertia is equal to the pull of gravity. However, the force of gravity is still acting on them. However, if they are in outer ...
1
vote
1answer
69 views
A block, a string and Newton's third law
So this is a general force diagram of the system shown. My question is, according to the third law, if the block is exerting a force of magnitude mg on the thread in the down direction, then the ...
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vote
0answers
19 views
Delivered/Reflected Power by Drive on a Hamiltonian System
Imagine a SHO with a drive F(t). (or in general a Hamiltonian system)
What is the power delivered to the system and can we talk about the power reflected? is i am imagining say a MW oscillator ...
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votes
2answers
520 views
Earth-Centered Inertial (ECI) reference frame as approximate inertial frame of reference
In many practical applications, one can consider the Earth-Centered Inertial (ECI) reference frame approximately as an inertial reference system, though strictly speaking, it is non-inertial.
Is ...
5
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2answers
337 views
Explanation that air drag is proportional to speed or square speed?
A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
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votes
2answers
61 views
What is the sensation by man carrying a water bucker with an object floating in it? [closed]
A man is carrying a bucket with water. If a object is kept in it which floats in water, man will feel
1) heavier
2) lighter
3) none
I think when the body floats its weight is balanced by upthrust ...
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votes
0answers
24 views
how to dot product in 3 dimensions? [closed]
i have two vectors, vector A = 12 and vector C = 15 . vector A makes 60 degrees clock-wise x-axis. vector C makes 45 degrees clockwise z-axis, 30 degrees counter-clockwise y-axis. i did not ...
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votes
2answers
205 views
Two blocks connected by spring on frictionless surface and Newton's third law
Suppose there is the following situation:
Blocks $A$ and $B$, with masses $m_A$ and $m_B$, are connected by a
light spring on a horizontal, frictionless table. When block $A$ has
acceleration ...
3
votes
2answers
69 views
Extension to continuous in proofs of rigid body mechanics
I'm studying rigid body mechanics and I've seen several proofs of properties related to total angular momentum, kinetic energy, etc. that all regard discrete set of points. For example, to show that ...
7
votes
3answers
194 views
What is the period of a physical pendulum without using small-angle approximation?
What is the expression for the period of a physical pendulum without the $\sin\theta\approx\theta$ approximation? i.e. a pendulum described by this equation:
$$
mgd\sin(\theta)=-I\ddot\theta
$$
...
12
votes
4answers
1k views
Newton's Bucket
Newton's Bucket
This thought experiment is originally due to Sir Isaac Newton. We have a sphere of water floating freely in an opaque box in intergalactic space, held together by surface tension and ...
3
votes
2answers
94 views
What is the physical significance of the off-diagonal moment of inertia matrix elements?
The tensor of moment of inertia contains six off-diagonal matrix elements, which vanishes if we choose the principle axis of the rotating rigid body and the components of the angular momentum vector ...
3
votes
2answers
60 views
Frictional Forces
In the figure, blocks A and B have weights of 45 N and 23 N, respectively. (a) Determine the minimum weight of block C to keep A from sliding if μs between A and the table is 0.21. (b) Block C ...
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2answers
1k views
History of interpretation of Newton's first law
Nowadays it seems to be popular among physics educators to present Newton's first law as a definition of inertial frames and/or a statement that such frames exist. This is clearly a modern overlay. ...
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votes
1answer
47 views
Friction force and contact area [duplicate]
It's usually stated that the friction force is independent of the area of contact (Amontons' Second Law).
I've always thought that this shouldn't be true, because the atraction between molecules ...
0
votes
1answer
202 views
Calculating a 2D collision between two perfectly circular disks
Assume I have two disks, $p_1$ and $p_2$, of radius $r$, with their own velocities (preferably in $(x,y)$ form, but $(m, \theta)$ works too) and masses (unit-less, but same unit) collide in two ...
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votes
0answers
108 views
Moving a minecraft earth a la Momo [closed]
In Michael Ende's classic novel Momo, a boy tells a story about an amphitheater. He says that a king once built a globe on the amphitheater, a scale model of the earth, except that the scale was 1-1, ...
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votes
1answer
51 views
What is the minimum wrap around angles of belt, timing belt and chain? [closed]
I read a website which said the minimum wrap around angle for belt on pulley is 120 degrees, However, it doesn't say whether it is belt or timing belt. Also I want to find the minimum wrap around ...
2
votes
2answers
48 views
Rotating spring system: Is my intuition correct?
Consider a solid spherical object of uniform density that is rotating on an axis A1. Perpendicular to that axis one can draw another line that passes through the sphere. On this axis, on both sides of ...
3
votes
3answers
102 views
Newton's First Law of Motion; Empirical Aspects
Newton's first law states that in an inertial frame, a body at rest continues to be at rest, and a body in constant rectilinear motion continues its motion, unless an external force is applied upon ...
0
votes
1answer
231 views
How should I apply conservation of energy to this problem?
A block rests on a table. Then the block is pushed by a spring and slides across the table until it falls to the ground. The mass of the block is $1.30\text{ kg}$, the spring constant $550\text{ ...
