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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Torque on object [closed]

I would like to understand why the torque on white object is 0. I know gravitational forces are very low. But the torque must be at 0. I drawn all the study in first image. Blue color is a torus of ...
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3answers
119 views

$P\sin(\alpha)$ and not $\sin(\alpha)/P$?

Why is the force parallel to the surface that pushes the object $P \sin(\alpha)$ and not $\frac{\sin(\alpha)}{P}$? I didn't understand when they showed me it. can someone give me an answer in full ...
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3answers
11k views

Vertical and horizontal components of forces and vectors

I'm getting a bit confused when finding components of vectors and forces. In problems for vectors, I've always known that if you want to get the components of a vector, you would use the following: ...
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2answers
250 views

Spring force vs Spring Potential Energy?

Which strategy should I use to approach a problem? Sometimes I'll use $U= 1/2kx^2$ when I should use $F=-kx$ and vice versa. What are clues in a problem that would let me identify the correct approach ...
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1answer
93 views

Reciprocating vs. rotating machines

Why is the RPM achieved on a reciprocating machine in general lesser than that obtained in a rotating machine? For example, an IC engine typically provides an RPM of about 2500 while a turbine can go ...
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1answer
1k views

Deriving D'Alembert's Principle

The wiki article states that D'Alembert's Principle cannot derived from Newton's Laws alone and must stated as a postulate. Can someone explain why this is? It seems to me a rather obvious principle.
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1answer
296 views

Work done by a variable force [closed]

The question asks to find the work done by the force $\mathbf{F(t)}=(4\mathbf{i}+12t^2\mathbf{j})N$ in the time interval $0\leq{t}\leq{1}$ on a particle of mass $4kg$, however I am not sure my working ...
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2answers
1k views

Explain what happens to object in lift [closed]

In the following image,three cases have been mentioned. $N$ is the normal force acting on the object inside the lift and $mg$ is the force of attraction due to gravity. In case 1, $N = mg$. In case ...
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1answer
302 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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2answers
234 views

Does a large uncertainty in a given value justify a large uncertainty in the result?

I'm working on a pre-lab for my Physics 1 lab session, and I had a debate with the person I carpool with (who is taking the algebra-based Physics 1 lab). We seem to be unsure about uncertainties, and ...
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1answer
492 views

Where do the equations for resistive force come from?

I've been watching MIT's Walter Lewin physics lectures. In lecture 12, Lewin pulls, out of nowhere, a couple of equations regarding resistive/drag forces in fluids: $$\begin{align} \vec{F_{res}} ...
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2answers
170 views

Does $y$-motion really have nothing to do with $x$-motion?

I am watching a Physics 1 for physical science majors on coursera.com, and in one of the concept tests there is a question that goes like this; "A bullet is fired horizontally from a rifle on the Moon ...
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1answer
368 views

Terminal Velocity Question [closed]

Question: A ball of mass m is thrown vertically upward with initial velocity $v_0$. Air resistance is proportional to the square of the velocity. If the terminal velocity of the ball is $v_t$, show ...
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1answer
87 views

Drag Force per point in the body

Let us consider the common equation for drag force for any body. $F_D = \frac{1}{2}\rho v^2C_dA$ Here the A is the representative area which is the so called area of cross section of the body for ...
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3answers
9k views

Kinetic energy and momentum conservation in an explosion?

My physics book says, "A firecracker sliding on ice has the same total momentum before and after it explodes." I understand this part. This is because of Newton's 3rd law, and no external forces. This ...
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1answer
128 views

Changing Momentum

Okay, so I am having a hard time wrapping my head around this. Before looking at the answer, I worked the example and got the answer only because I used dimensional analysis to get me to the right ...
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3answers
328 views

Does GR imply a fundamental difference between gravitational and non-gravitational acceleration?

Does the equivalence principle imply that there is some fundamental difference between acceleration due to gravity and acceleration by other means (because there is no way to 'feel' free fall ...
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1answer
464 views

Details of the new solutions to the three-body problem [closed]

This question is part of this week's Journal Club session. These systems look ridiculously fun to construct. Could someone explain the particulars? What are the various types of solutions, and ...
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1answer
772 views

Direction of friction in case of a rolling sphere

Suppose a ball rolls on a ground .obviously it is friction that helps to develop the required torque.Hence I find the direction of friction by pointing out the direction of rolling of the ball. But is ...
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1answer
124 views

Is the trajectory of the Moon around the Earth stable? [duplicate]

I understand how mathematically is possible to have one object with elliptical or circular orbit around another object in space. so can I think of it as a limit cycle? If yes, then is it stable or ...
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2answers
731 views

Calculate the acceleration of a moving elevator [closed]

An elevator is moving down with uniform acceleration. A man inside the elevator who wants to measure the acceleration drops a coin as soon as the elevator starts. The coin is 6ft above the floor of ...
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2answers
614 views

Force, constant velocity, and 0 velocity

When a body has a net force of 0 on it, one cannot say that it is at rest or in motion at a constant velocity. If a body is accelerating because of some force and I want to stop it, I can apply the ...
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4answers
2k views

How did Newton discover his third law of motion?

How did Newton discover his third law? Was it his original finding or was it a restatement of someone else's, like the first law coming from Galileo? What initiated the concept of what is now known as ...
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2answers
2k views

Normal force and reaction

It is said that the normal force comes into play any time two bodies are in direct contact with one another, and always acts perpendicular to the body that applies the force. This force is a ...
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1answer
3k views

Does a force do work on an object with constant velocity?

I know that a force does no work on an object if the object's displacement is zero, but if an object is moving at a constant velocity $\bar{v}$, and a force $\bar f$ (let's say that $\bar f$ and $\bar ...
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3answers
727 views

Why does a bicycle come to rest after travelling a distance?

According to Newton's law of motion, an object that is in motion will not change its velocity unless an external force acts upon it. In the case of a bicycle, if it is in motion with a certain ...
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1answer
2k views

Cylinder rolling down slope problem [closed]

A uniform cylinder of mass $m$ and radius $r$ is rolling down a slope of inclination $\theta$. The cylinder rolls without slipping. You may take the acceleration due to gravity to be $g$. At what rate ...
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1answer
589 views

Force on impact in case of a free fall

In a free fall, on impact with the ground, the body experiences a massive force because of a huge acceleration since the velocity goes to 0 rather quickly. Since this force has to come as a result ...
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7answers
3k views

Intuitively, how can the work done on an object be equal to zero?

To my understanding the work done on an object is defined mathematically as: $$W = \vec{F}\cdot\vec{S}=|\vec{F}||\vec{S}|cos\theta$$ This, I understand. My problem is that I don't understand that if ...
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3answers
1k views

Why does a bicycle (without any support of stand) falls down being at rest, but not under motion? [duplicate]

I have always seen a bicycle not standing without any support, it either falls down to the right or to the left, may even to some other direction. But,the same two wheeler when under motion,moves ...
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3answers
18k views

Why work is a scalar and not a vector?

Work (in physics) is a scalar, but why? And why not a vector?
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0answers
47 views

Acceleration of 2 bodies tied with a string [closed]

Find the acceleration of the block of mass M shown in the figure . The co-efficient of friction between the 2 blocks is μ1 and that between the bigger block and ground is μ2. Could someone help ...
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1answer
149 views

Does Archimedes law depend of lack of matter?

I would like to know if Archimedes law take in equation the lack of matter. Fluid density at 1. An object with density of 0 (or near 0) is put in liquid, it's fixed. The external sphere where liquid ...
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3answers
317 views

Is the Normal force dependent on the density of the object the body is resting on?

If a body is resting on the ground, the Normal force equals its weight. If I keep putting another body on top of it, eventually the body will start moving into the ground until the new Normal equals ...
2
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0answers
506 views

Loop-the-Loop with Friction [closed]

Let's consider a track that begins vertically becomes a 450 degree loop, and level off. (See diagram) We drop a block from height $H$ that falls and goes around the loop. Ignoring air resistance, ...
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12answers
4k views

Where does the extra force generated by a lever come from?

Given an object being pulled down to earth by a force of 1000 lb: If a machine were to lift it off the ground for me, and I grabbed on to the rope before it was released, there is no way in the world ...
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3answers
578 views

Does a heavy body move with the slightest force on a frictionless surface?

If I apply horizontal force on a body resting on the ground, my force will be opposed by the frictional force and the body will accelerate at the point where my force exceeds the force of friction = ...
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0answers
103 views

Seeking help simplifying this EOM equation

I am working on solving the equation of motion for a particular system. It has been a long time since I've worked with matrix equations and need help in simplifying the following: ...
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2answers
13k views

Perfect elastic collision and velocity transfer

So my teacher told me that when you have two identical balls in a perfectly elastic collision, the first ball A will collide with B and afterwards A will stop and B continue. Why is this? Doesn't ...
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2answers
248 views

Weighing a flying bird [duplicate]

Let thing of a bird standing still in a box on top of a weighing machine that shows a mass $m_0$. Now, imagine that the bird is flying, still in the same box and the same weighing machine shows a mass ...
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2answers
184 views

How to work out the acceleration of an object

I got given this question and im just lost. An object that weighs 25 kg experiences two perpendicular forces of 80N and 50N respectively. What's the acceleration that object gets? What i ...
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1answer
159 views

Conservation of classical linear momentum

Imagine a cat jumping off a roof onto a sledge on ice. Model this as simply as possible, e.g. no resistive forces, perfectly rigid cat, sledge and floor. Moreover, the cat and sledge move in a ...
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3answers
924 views

Block and inclined plane (INPhO Problem)

The figure shows two blocks on an inclined plane of mass 1kg each.The coefficient of static as well as kinetic friction is $0.6$ and angle of inclination is $30^\circ$ . Find the acceleration of the ...
9
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4answers
799 views

D'Alembert's Principle: Necesssity of virtual displacements

Why is the D'Alembert's Principle $$\sum_{i} ( {F}_{i} - m_i \bf{a}_i )\cdot \delta \bf r_i = 0$$ stated in terms of "virtual" displacements instead of actual displacements? Why is it so necessary ...
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2answers
129 views

Elementary physics question…requires calculus?

A 2500.0kg car is going at a constant velocity of 14.0 m/s and hits the breaks to stop. It skids 25m. What is the coefficient of friction of the tires to the ground? So I have acceleration = -4.0 ...
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2answers
493 views

What does “along the handle of the cart” mean? And how does one calculate weight?

A horizontal force is used to pull a $5.0\text{ kg}$ cart at a constant speed of $5.0\text{ m/s}$ across the floor. The force of friction between the cart and the floor is $10\text{ N}$. ...
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1answer
59 views

How can enzyme/substrate reactions that adhere (largely) to quantum theory also require 'Newtonian' consideration of gravity?

I'd just like to ask for a little clarification here due to confusion from interdisciplinary studies. I'm currently reading the 1976 paper related to the recent 2013 Nobel Prize for Chemistry, by 2 ...
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3answers
521 views

How can a block which is not receiving the direct force have a greater acceleration?

I solved it like this: $$F(\text{st max})=5\text{ N}$$ For the top block, $$\begin{align} 6\text{ N} - 5\text{ N} &= 1a \\ a &= 1\ \mathrm{m/s^2} \end{align}$$ For the lower block, the ...
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0answers
160 views

N-body forces in classical mechanics

For a system of two interacting particles 1, 2 we get from the conservation of momentum $$ \dot{\bf{p_1}} + \dot{\bf{p_2}} = 0$$ ...
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3answers
152 views

Why heavier bodies produce greater gravitational pull than the lighter bodies?

The basic question "Why planets revolve around the Sun?", is explained by taking into account the heaviness of Sun. The lighter bodies are considered to move around heavier bodies,as like lighter ...