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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What is the outward force on the Moon that makes it go in orbit rather that falling straight to the Earth? [duplicate]

So, we know that the gravity is responsible for pulling the Moon towards the Earth. But because it moves in an orbit, it makes me think that there must be a force that is causing the moon to travel in ...
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2answers
4k views

If action equals reaction, how is it ever possible to win in martial arts?

In kick-boxing, when a fighter's leg hits an opponents leg, the outcome, based on Newton's 3rd law, should be the same for each fighter. It's not even important who kicked who, as in the moment of ...
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1answer
107 views

Understanding $F=ma$

I know the formula F=ma, but I truly need to understand its implications. Take this scenario for example, we have two bullets exactly the same weight and size (identical to each other). Lets assume ...
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1answer
530 views

Two objects at different heights, would they be traveling the same speed?

If I were to drop an object at a height of 15 feet, then another object of the same mass at 20 feet, would both objects be traveling at the same speed? What would be the speed of which they are ...
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2answers
178 views

Apply force to one end of a rod in space: why not purely translational? [duplicate]

Why does applying force to a rod in space (or any other isolated systems) on one end leads to both translational and rotational motion? Here's my logic: suppose there is a rod in space. We ...
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154 views

Action and Reaction between two people

When you hit a person, you apply a force on him. Then according to Newton's third law, there should be an equal and opposite reaction, and that should act on you. So, why don't you fall backward? Is ...
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77 views

Finding velocity from distance and gravity

Basically, I have a problem that asks: An object is launched to a height of 2 miles, what was it's initial speed and time. Now normally something like this would be fairly basic. The problem ...
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93 views

Would a titanium suit save your life from a piano falling on you? [closed]

Or would the piano dent the titanium and kill you?
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28 views

How to write the moment equation about a rotating as well as translating point?

I want to write the moment equation in Ground frame as well as the frame of reference of the point (which I think should be a rotating frame of reference) for the following situation. $C$ is the ...
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51 views

Find $\oint xdx+2ydy+3zdz$ on the line segment formed by points $A(1,0,-1)$,$B(2,5,-1)$ [closed]

Find $\oint xdx+2ydy+3zdz$ on the line segment formed by points $A(1,0,-1)$,$B(2,5,-1)$ My approach: First I find the line segment formed by $A,B$ which is $\vec l(t)=\vec{OA}+t\vec{AB}=(1,0,-1)+t(1,...
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358 views

Are Newton's laws followed in non-inertial frame of references having all their objects and observer moving with same acceleration?

Consider a hypothetical scenario. In our universe there are two merry-go-rounds 1 and 2 and a distant planet. There is no other object having mass. There is a robot X on the planet. There are two ...
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507 views

Variation of Kinetic Energy

Question: Which of the following graphs correctly describes the variation of kinetic energy with time of a block when it slides down a smooth inclined plane from rest? The answer is C but I do not ...
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98 views

Why do Lagrange multipliers work in mechanics?

I understand that it is not always simple to find generalized coordinates that satisfy the constraint equations, so we try to find an alternative (more mechanical) method that yields curves that ...
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2answers
53 views

Does $v^2=v_0^2-2gh$ work if the positive axis is up and the initial velocity is down?

In the situation where the positive axis is up, the acceleration due to gravity is $g$, and the velocity is represented by the equation $v^2=v_0^2 - 2gh$. This works great if the initial velocity is ...
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1answer
87 views

Circular motion with friction (time dependent velocity)

I am trying to understand how circular motion problems can be solved when we introduce friction as a variable in them. As i understand this problem, the centripetal force, which points towards the ...
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0answers
86 views

Are new discoveries in quantum physics (e.g. Amplituhedron) supporting one of the classical QM interpretations? [closed]

Are new discoveries in quantum physics (e.g. Amplituhedron, Higgs boson) supporting one of the classical QM interpretations? For example Copenhagen, Everett many worlds or Penrose interpretations. Or ...
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848 views

In wave motion of a string both kinetic energy and potential energy are minimum at $y=y_\text{max}$ then why does the string comes down again?

In wave motion of a string both kinetic energy and potential energy are minimum at $y=y_\text{max}$ then why does the string comes down again? As everything in tries to attain lowest energy possible ...
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1answer
88 views

Will dynamo generate electricity with reverse spin?

Will a dynamo generate electricity when it is spinning in opposite direction? If we alternate the rotation direction every minute, will it still generate electricity? How?
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31 views

Is it possible that any spatial variation in press disturbance without gravity?

When gravity (and buoyancy), acting as the only body force of a liquid, is ignored. Is it possible that any spatial variations in pressure perturbation are the result of fluid motion or some other ...
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1answer
83 views

How to set up equations of forces for 3 springs connected to each other in an elevator?

In the above diagram the elevator is moving downward with acceleration $a_E$ and velocity $v_E$. All 3 masses are given as $m1,m2,m3$. The question is how much has the middle spring stretched from ...
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43 views

Collision and resulting compression

During collision is there any compression of the surface? if yes, the collision is considered as elastic or non elastic ? Does the compression produce the impulse force or its due to the impulse ...
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25 views

Size of meteor-made crater [duplicate]

I am reading "What if" piece https://what-if.xkcd.com/20/ and I am very interested in how can one ever estimate the size of a crater? How can you ever know, it must depend on energy of a falling body ...
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208 views

Why is the apparent weight smaller when you crouch down on a scale?

I am having a problem understanding the concept of the apparent weight change when you crouch down, stand up, and jump on the scale. What is happening that makes the scale change?
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1answer
320 views

2D Mass Spring System - Where does $m_3$ go to?

I am struggling to frame proper equations for the following two-dimensional mass spring System: 1D Model Basics first: I started with a simple one-dimensional mass-spring System to model something ...
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423 views

How do you calculate the output force of a machine?

Based on a force inputed in a machine, how do you calculate the force outputed? I would have thought you could do this with a simple torque balance but this does not always appear to be the case. For ...
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52 views

Bending + Contact Force

When we have 2 bodies in contact with each other, for example a book lying on the surface of a table. The table's molecules bend a little bit because of the weight of the book thus producing the ...
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1answer
83 views

Determining the instantaneous axis of rotation [closed]

Given the following image The question states ,a heavy disc with radius R is rolling down hanging on two non-stretched strings wound around the disc very tightly.THe free ends of the strings are ...
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1answer
61 views

How much power is needed to drive two times faster?

Suppose a cyclist riding at speed $v$ decides to accelerate to speed $2v$. Does she have to generate $8$ times more power to sustain that speed? $P_1=F_dv$ If we double the speed, (it usually ...
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2answers
891 views

Work done by a non-conservative force and change in potential energy

I know that the work done by a non-conservative force is equal to the change in total mechanical energy (from Work-Energy Theorem). But I read in a place that "Non-conservative forces don't affect PE"....
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31 views

Can you explain the dynamic of forces working in the video?

Lifting Against Gravity - Breaking Magic - Discovery Channel In this video, a woman uses Physics, so that it is difficult to lift her off the ground. The explanation that the video gives at the end ...
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133 views

Is friction a function of surface area? What is the microscopic workings of friction?

I know the friction is given by the following equation $$\mu F_N=F_f$$ which tells me friction is independent of surface area, but how do I characterize it as such if I want to add surface area into ...
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1answer
21 views

What topic and equations will characterize the pulling and breaking of a piece of wood [closed]

Let's say hypothetically I pull on a wooden rod from both opposite ends The rod then breaks in half at the center What equations govern this. Is it an engineering problem with things to do with ...
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Average Force vs Net Force

The F in $$Impulse = F*t$$ is said to be the average force. For a ball dropped vertically onto a horizontal surface, the average force, F, on the ball from the floor is: $$F = \frac{\Delta{p}}{t}$$ $$\...
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150 views

Question about Torque Reaction of a Helicopter

This image below about the torque reaction of a helicopter has confused me a bit. I would like to ask whether i understand the principles here correctly. In the picture we see a helicopter whose main ...
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27 views

Power exerted by the contact force on a wheel slipping without rolling?

I was taking an old (2008) Mechanics of materials examination, and the system is a sphere on a half circular motionless rail. We first study the motion of the sphere in the case of rolling without ...
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50 views

Another elevator question..?

I read in a book that if a lift descends with an acceleration of more than 9.8 metre per sec squared , the person would strike his head on the ceiling of the lift . I did the calculations and yes the ...
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420 views

How to apply Newton's Third law when a massless spring is compressed by a moving block?

I was really confused about the applicability of Newton's Third Law in case of non-rigid bodies like springs. While googling about this I read that Newton's Third Law fails in case of springs. I saw ...
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58 views

Calculating and modifying trajectory

I am busy working on a programming puzzle which is rather fun. The help I'm looking for is not with the coding as such but the physics behind it so I thought I'd turn to the Physics stack. The ...
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3answers
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Confused on how tensions can differ with angle

So I understand the mechanics of resolving forces via Trig, what confuses me is how the tension can change. Imagine you have a 100N weight suspended from a rope tied to 2 points. It seems to me (but ...
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70 views

What is the main key to distinguish the oscillator from the two system?

Let a circular hoops of radius $r$, is hanging on nails in a wall. Can I consider this as simple pendulum so the frequency $\omega = \sqrt{\frac{g}{L}}$? On the other hand If I consider that ...
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176 views

Doubt on a question from Newton's laws of motion

We(me and my classmates) had completed a chapter on Newton's Laws of Motion. Now this question pops up: A cricket ball of mass $70\,\mathrm{g}$ moving with a velocity of $0.5\,\mathrm{m/s}$ is ...
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2answers
162 views

Gravitational Null Point between Earth and Moon

I need help finding the gravitational null point point between the Earth and the Moon, the point beyond which you start falling towards Moon. I am having difficulty in taking into account the orbiting ...
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147 views

Why would the relationship between period and mass be important to you in a Simple Harmonic motion?

My lab's teacher always asks us why we're there at lab before the class starts. We already know the variables we're supposed to measure, so we frequently say (We used to say): "We want to find out the ...
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1answer
117 views

A question on Rolly polly dolls

I was reading on rolly-polly dolls when the following questions crept into my mind How exactly does center of gravity play a role which helps rolly-polly doll to stand up on its own? Can a rolly-...
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1answer
85 views

Gravity Relative to Mass?

Why is it that, in basic physics, it is taught that the acceleration of gravity is the same for objects of any mass (at a constant distance from earth)? Why then is the acceleration of gravity ...
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71 views

Would the system exhibit periodic motion? [closed]

A mass moving in one dimension has a potential energy given by :- $$V(x)=\frac{k_1}{2}x^2+\frac{k_{2}}{x}$$ where $k_1$ and $k_2$ are positive constants and $x>0$. Is this system exhibiting ...
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238 views

Momentum is conserved without the application of Newton's third law in cases of non-rigid bodies like spring

Let a spring be attached with a block moving with $v_1$; when another block with velocity $v_2(v_2 \gt v_1)$ hits the spring from the rear end, the spring gets compressed until both the blocks have ...
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1answer
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What is meant by saying the work done by a conservative force is -(change in PE)?

I read through all related questions, and they are almost the same, but I still didn't understand this and so am asking again. What is meant when we say that the work done by conservative force is = -...
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2answers
98 views

Is there any loss or gain of information if a physics law is changed from one form to another? [closed]

Is there any loss or gain of information if a physics law is changed from one form to another such that the parameter appearing in them is changed from vector to a scalar? For example, consider the ...
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54 views

Third law of motion when action and reaction are separated by some time

For every action there is an equal and opposite reaction. I have used this law only when bodies are in contact with each other which means for every action reaction is produced at same instant of time....