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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300 views

Walking and Friction

If walking is a result of the reaction to a kick backwards to the ground (reaction being friction), it appears that it should be true that the kick will have to be less than the kinetic friction ...
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25 views

Torque due to non-uniform force [closed]

Suppose a non-uniform force, varying along with the distance, is acting normally on the surface of a rod hinged at the mid point. The force varies along the length of the rod, i.e as we go down along ...
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2answers
34 views

If I flex my arm, where is the “equal and opposite” reaction?

In my sight, nothing happens at all. Is the opposite reaction pressure applied to my bones? It certainly seems so; however, since I flex my arms in a curve, shouldn't the opposite reaction direction ...
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1answer
42 views

Why, in a car taking a sloped curve, friction is perpendicular to the car

In solving the problem we usually use the friction as the centripetal force, but I could never understood how is this possible. I understand that if a car is making a circular motion, some centripetal ...
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6answers
755 views

Why is momentum conserved (or rather what makes an object carry on moving infinitely)?

I know this is an incredibly simple question, but I am trying to find a very simple explanation to this other than the simple logic that energy is conserved when two items impact and bounce off each ...
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0answers
25 views

Why does kinetic energy quadruple when speed doubles? [duplicate]

Why does kinetic energy quadruple when speed doubles? Please explain (in simple terms) with examples if possible.
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1answer
49 views

Kettlebell squats center of mass

I should, first of all, state that I have very limited knowledge of physics but as a fitness enthusiast the following question has puzzled me for a while. When I do squats on the gym holding a ...
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2answers
90 views

Why does a reaction force still allow the thing exerting the force to move?

A $5$ kg and a $10$ kg box are touching each other. A $45N$ horizontal force is applied to the $5$kg box in order to accelerate both boxes across the floor. Ignore friction forces and ...
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0answers
12 views

Does the force of releasing the latch of a spring-latch contraption affects the force generated by the spring?

There is this contraption in my class, where a rod is attached to a latch and a spring. By pulling the latch back behind a piece of metal, the latch is secured, the rod if pulled back and the spring ...
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1answer
103 views

You are trapped on a frictionless sheet of ice. Can you escape by inhaling in one direction, then exhaling in the opposite direction?

You are trapped on a frictionless sheet of ice. If you trued to escape by blowing, you would have to inhale eventually, which would counteract the force you gained by blowing. However, if you were to ...
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1answer
63 views

Feynman Lectures: Resonance - Problem with Formula

I am reading Volume 1 Chapter 23 of FLP, and I have come across something rather strange. Feynman says that: $$ \rho^2 =\frac{1}{m^2[(\omega^2-\omega_0^2)^2+\gamma^2\omega^2]} $$ A graph of this can ...
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2answers
72 views

Which of these two forces is stronger: static friction or kinetic friction? [duplicate]

Which of these two forces is stronger: The force of static friction or the force of kinetic friction? I am having a hard time understanding this concept of friction, so please explain your answer!
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31 views

$\mathbf{P}=M\mathbf{v}_{cm}$ for a continuous body?

While restudying some fundamental concepts with greater attention, I have reflected on the following deduction, which I find in my book of mechanics, of the identity of the temporal derivative ...
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2answers
26 views

Risk assessment for ablation of Earth-collision course object

I have seen articles dismissing fragmentation of an incoming Earth-colliding object as too risky because of resulting collisions of smaller resulting pieces. What would be the adverse effect of ...
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4answers
971 views

When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?

If there are two hydraulic cylinders connected in parallel, each with a different load (shown in the picture below), will they start extending at the same time? I'm having a disagreement with my ...
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3answers
10k views

About an upside down cup of water against atmosphere pressure

There is an experiment we learned from high school that demonstrated how atmosphere pressure worked. Fill a cup of water and put a cardboard on top of it, then turn it upside-down, the water will not ...
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1answer
43 views

Rigid body: internal work null?

I am following an elementary physics course book, namely W.E. Gettys, F.J. Keller and M.J. Skove's Physics (in an Italian translation). In exercises where no non-conservative force acts on a rigid ...
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3answers
74 views

Why can't I harness normal force?

Lets say I have my palm flat with a book resting on top of it, and I have my feet on the ground. I extend my arm so that now it's kind of difficult to keep the book up. Why doesn't my hand just ...
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3answers
78 views

Time period related to acceleration due to gravity

The period of a pendulum is given by $$ T = 2\pi \sqrt{\frac{L}{g}}. $$ If we take a pendulum where there is no gravitational field, then $g=0$, therefore the period should become infinity. In such a ...
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1answer
98 views

A moving brush on a vibrating surface

Hi group, I am a HS student in China preparing for a regional Young Physicist Tournament even. We are very puzzled about why would there be such movement. We would be grateful to see any inspiring ...
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3answers
98 views

How is a ballistic pendulum affected by two objects with different mass?

Imagine that bullet A (made of lead) has twice the mass of bullet B It is shot at the same muzzle velocity as bullet B onto a ballistic pendulum; all other initial variables are the same: size and ...
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0answers
44 views

Total angular momentum of a continuous body

I find the definition of total angular momentum $\mathbf{L}$ of a system of $n$ material points with respect to a given point $Q$ as the sum of the momenta $\ell_i=\mathbf{r}_i\times\mathbf{p}_i$ ...
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0answers
37 views

The behaviour that saves more energy/ petrol when driving down-up-hill [closed]

This question is in a way a follow-up of this one: Can a car get better mileage driving over hills?, it is similar to that, is no engineering question and is in no way a homework problem, I'd like you ...
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1answer
44 views

Normal force on a banked road & why it's larger than the gravitational force here

Please read this: http://www.askiitians.com/iit-jee-physics/mechanics/banking-of-roads.aspx From my understanding of normal forces, they are a reaction to gravitational or other forces. When a force ...
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2answers
314 views

Relative motion. Setting course of closest approach

Let $r_{P/Q}$ be the position vector of $\overrightarrow P$ relative to vector $\overrightarrow Q$ and $v_{P/Q}$ the velocity vector of $\overrightarrow P$ relative to $\overrightarrow Q$. Suppose ...
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4answers
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Does a truck stop faster if the stack on the back of truck is stable or if it moves forward?

My question in the title might not be very descriptive so I am re-writing it here: If there is a truck in motion and it has stack of hay (lets suppose) on the back. Now if the truck comes to a sudden ...
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1answer
64 views

Analysis of a card pyramid

Here's an interesting question I thought of. Firstly, picture one of those card pyramids. Hopefully you know what I'm taking about when I say card pyramid, but basically you balance two cards up ...
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3answers
51 views

An elevator accelerating upward, tension increases in the rope to which a fish hangs inside the elevator why?

A fish is hanging in an elevator through a rope, when elevator accelerates upward the tension in the rope increases why? When elevator accelerates downward the tension in the rope decreases why?
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1answer
62 views

Are there any exceptions for law of conservation of angular momentum?

I just wrote a medical entrance test, in which this question appeared a person sitting firmly over a rotating stool has his arms stretched, if he folds his arms, angular momentum about the axis of ...
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1answer
152 views

Calculate orbit height from tangential velocity

Is it possible to calculate the altitude of a satellite orbiting a planet, just from the planet's mass and the satellite's velocity, assuming that the satellite is in a perfect circular orbit? If so, ...
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1answer
291 views

Coriolis deflection:- is it 4 times if the object is thrown up, compared to a drop?

A particle is thrown up vertically with initial speed, reaches a maximum height and falls back to ground. Show that the Coriolis deflection when it again reaches the ground is opposite in ...
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3answers
1k views

Looking for an intuitive understanding of normal force

I understand normal force to be the perpendicular force to a surface of contact. However, I have come across a problem which has caused me to rethink this. My initial understanding of force is ...
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2answers
84 views

Proof of Newton's second law [duplicate]

Is it possible to prove Newton's second law of motion, $F=ma$? Or is it just realized because of proportionality and the definition of a Newton of force?
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2answers
141 views

Dropping a weight onto a spring scale

Say I drop a 5kg weight from a height of 1 meters onto a spring scale like many people have in their bathrooms. On impact the scale will show a higher weight than 5kg. Question: Which quantities ...
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0answers
19 views

Spring limitation

Is there any limitation in acceleration and frequency of a spring. Please, imagine a horizontal spring with an object of mass $m$ attached in the free side and the friction is neglected. ...
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5answers
979 views

Electron shells in atoms: What causes them to exist as they do?

I have seen similar posts, but I haven't seen what seems to be a clear and direct answer. Why do only a certain number of electrons occupy each shell? Why are the shells arranged in certain distances ...
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2answers
54 views

Why does friction act on a cylinder rolling on an inclined?

When a cylinder performs pure rolling while on an inclined plane, Why does friction act on the bottom point? In pure rolling the bottom most point is at rest, so there is no sliding over ...
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2answers
130 views

If Earth and Jupiter are orbiting around Sun in same orbit, will they have same time period?

Let us suppose that Earth and Jupiter are orbiting around the Sun in same orbit, If we talk about at any particular point. (Which is not possible but for the sake of question) I was wondering that ...
2
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1answer
100 views

Weightless person in a cart on a rail [closed]

In a problem I'm trying to solve I'm having a conflict between my understanding and the proposed solution of the problem. In the problem, a cart of mass $m$ is put at rest in the start of a ...
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0answers
25 views

Mechanics - Rotational Inertia [migrated]

I am facing a problem solving a mechanical system which is shown in the scheme below. We assume that coupling of the two shafts is done with a clutch Equations: ...
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1answer
69 views

Why doesn't atmospheric pressure crush thick walled structures?

There is one thing that puzzles me: common explanation of why don't structures collapse under the enormous atmospheric pressure (~101300N/m^2) is that the force pushing from inside balances out the ...
3
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1answer
51 views

Determining straining force and reaction forces on a beam [closed]

A homogenous beam $OA$ with the length $4a$ and the mass $m$ can rotate in the vertical plane along a horizontal axis through $O$ and is kept in equilibrium by a wire running from the points A and C ...
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2answers
81 views

Is there a normal downward force here?

Now through my understanding, there is a weight force that points downward on block A, also another weight force that points downward on block B. Between block A and block B, there is two normal ...
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1answer
64 views

Two equations for $y$ in projectile motions

I have two equations on my equation sheet: $$y=v_o t \sin \theta - \frac{1}{2} g t^2.$$ $$y_{\max} = \frac{v_o^2 \sin^2\theta }{2g}.$$ I understand that the first one is an equation for the height ...
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0answers
71 views

Interesting approach to Kepler problem

I won't go into the explanation of this idea, because it is explained in this blog post. In this paper, which was featured on John Baez's blog, $\frac {dt}{d\lambda}$ is given as $\frac r V$, where ...
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1answer
435 views

Relative wind velocity explanation - understanding Irodov problem 1.6

I am having trouble understanding the reasoning behind the solution in this Irodov General Physics problem. The problem is 1.6: 1.6. A ship moves along the equator to the east with velocity vo = ...
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6answers
2k views

Can you ever exert more downwards force than your weight?

So, because I'm a hardcore person, I risked all this afternoon by going out in the wind, the rain and the cold to construct a willow den. Yes, it seems a menial task, but it was actually quite ...
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3answers
409 views

Would this box on the floor rotate based on friction?

There is a floor that friction is proportional to its velocity (like $F=-kv$) and there is a box with its width as $l$ and its height as $h$. (you may assume that $l$ is longer than $h$). It is on the ...
4
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1answer
73 views

General construction of equations of motion for free particles

I've got a question regarding the different Symmetrie-Lie-Groups of Newtonian Mechanics and special realtivity. Is there a canonical way to obtain the equations of motion for a free particle only by ...
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1answer
138 views

Spring Stiffness Calculation Problems

This may sound like a trivial question but please hear me out. I am trying to model a 1 DoF electromagnetic vibration sensor (geophone) analytically and with finite elements. A geophone consists of ...