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 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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40 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
165 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
78 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
266 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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28 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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3answers
18k 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
73 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
494 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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60 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
51 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
72 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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4answers
2k views

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
516 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
1k 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
240 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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3answers
2k 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
565 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
515 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
47 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
2k 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
185 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
222 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 ...
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3answers
113 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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1answer
160 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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1answer
75 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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88 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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6answers
4k 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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1answer
94 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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2answers
168 views

Centre of mass of a system of particles

If the centre of mass of a system of particles is at the origin, does this mean that if there is a particle on the positive X-axis, there must be atleast one particle on the negative X-axis? I feel ...
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1answer
57 views

Angular velocity in central force field

For motion in a central force field consider a rotating reference frame, which is characterized by the Euler angles $\alpha$, $\beta$, $\gamma$ associated with the rotation of the frame of Cartesian ...
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1answer
228 views

Newton's Third law of motion: A hammer hits a wall vs. hits a tire

When we hit the wall by a hammer, Newton’s third law says that hammer applies force on the wall (action) and wall applies force on hammer (reaction) equal in magnitude but opposite in direction ok ...
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1answer
68 views

Average force for repeated elastic collisions

I was asked to compute the average force exerted by a rigid spherical ball (mass $m$) on the floor over time $t \rightarrow \infty$, in a situation where the ball is dropped vertically from a height ...
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1answer
27 views

Inertia of a body cancells some amount of force?

If we have a block on a frictionless surface and we apply force F on the block to accelerate it, some amount of applied force will be cancelled by the inertia of the block am I right?
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23k views

How is distance between sun and earth calculated?

How has the distance between sun and earth been calculated? Also what is the size of the sun?
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3answers
2k views

Distance traveled by a water jet

I helped my kid in a science fair project, where we punctured holes in a water bottle at various heights and then measured the distance traveled by the water jets before they hit the ground. The ...
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1answer
66 views

Newton's law for rigid bodies

Is newton's third law valid for rigid bodies? Say, if we have a bullet hit on a rod which is vertically placed on a rough floor. Friction is just sufficient sp that the rod rotates and does not ...
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1answer
1k views

The choice of pivot point in non-equilibrium scenarios [duplicate]

It is true that under equilibrium condition, no matter what pivot point one choose, the resulting net torque will always be zero. I wonder if this principle apply to non-equilibrium scenarios as well, ...
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2answers
113 views

Resulting force when bending plywood

My sister and I are working on a thesis in interior design on a plywood chair similar to the picture, where the red part bends. We are trying to work out how much the plywood would push back when a ...
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2answers
308 views

Work done by frictional force on a sliding block

A block slides across a table horizontally with an initial velocity $V$. The frictional force $F$ brings it to rest after its Centre of Mass covers distance $S$. What is the work done by the ...
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3answers
94 views

On a scale, why does the heavier object go down?

When you balance a pencil on your finger, I have always wondered, "Why does the heavier part go down, and the lighter, up?"
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0answers
86 views

Calculating the 3-dimensional torque on a non-uniform rigidbody given the angular acceleration about its center of mass

Say I have a rigidbody, made up of several point particles with known masses and positions relative to the center of mass. How would I find the torque on this rigidbody given its angular acceleration ...
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1answer
135 views

When will the pringles can fall?

When I'm pushing a tall, cylindrical object stood on its end (like a Pringles can) I can push it near its bottom, and it will slide forwards, or push it near the top, and it will topple over. So, ...
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2answers
3k views

Finding maximum speed in a work-energy problem [closed]

I have the following problem: The Royal Gorge bridge over the Arkansas River is $310\text{ m}$ above the river. A $57\text{ kg}$ bungee jumper has an elastic cord with an unstressed length of ...
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0answers
23 views

Does relativity in any way “disprove” Newton? [duplicate]

I was reading a science magazine and it claimed that Einstein's theory of relativity disproves all of Newtonian physics. I was highly skeptical because all we have been learning at school is Newtonian ...
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1answer
177 views

Does mass distribution/center of mass affect free fall?

An everyday is example would be cars. If you were to drop a car, not taking air resistance into account, would a front-heavy car tumble forward as it fell? And a car with a perfect 50/50 front/rear ...
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1answer
46 views

Working out length of taut rope orbiting the earth remaining straight and radially directed [closed]

A taut rope is orbiting the earth with angular velocity $a$. It remains straight and radially directed. If the midpoint is located at radius $r$, find the length of the rope. I can't even imagine ...
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4answers
1k views

Paradox in applying Newton's second law [duplicate]

Suppose I apply two vertical but opposite forces with the same magnitude in a body like is shown in the picture: According to newton's second law, the center of mass shouldn't accelerate, since the ...
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1answer
2k views

Calculating torque in 3D?

Say you have a sphere, and you have several torque vectors acting on it, all at different points. Say you have the vector (6i + 3j + 5k) originating from point A, and the vector (3i + 1j + 9k) ...
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3answers
234 views

Work-Energy conservation with friction

I didn't go to the lesson of work-energy theorem, so I miss something about this subject. I know the formulas, but I can't figure it out. This question has many quantities. Here is the problem, ...