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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Semi-major axis and ellipticity of a binary system?

In the image below (source at bottom), it seems to be suggesting that \begin{equation} a = a_{1} + a_{2}, \hspace{8cm}(1) \end{equation} where $a_{1}$ and $a_{2}$ are the semi-major axis of the ...
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742 views

How does this chair move?

I have a chair like this(shown in figure). I was kneeling on the part where we sit. I just gave a sudden push to the part where we rest the back, without moving my legs. I found that the chair is ...
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238 views

Is air drag equation in term of momentum still valid?

This is the known equation of air drag: $$m{\bf a}=mg-\mathcal D=mg-b{\bf v}.$$ Considering this, is air drag equation in term of momentum still valid? $$m{\bf v}=mv_g-b{\bf r}.$$
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Kinetic Energy And Rotational Motion

The problem is, "A metal can containing condensed mushroom soup has mass 220 g, height 11.0 cm and diameter 6.38 cm. It is placed at rest on its side at the top of a 3.00-m-long incline that is at ...
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337 views

Conservation of Linear Momentum with respect to a given direction

Is linear momentum conserved in any direction? More specifically, if you project all momentum vectors in a system onto another vector, will momentum be conserved? I know that momentum is conserved ...
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Same momentum, different mass

The question is: if A bowling ball and ping pong ball are moving at same momentum and you exert same force to stop each one which will take a longer time? or some? which will have a longer ...
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Simple derivation of the tension of a cord on a suspended mass

Just wanted to disclaim this problem -- it is homework. However, I am not asking for the solution, I am wondering if anyone can tell me what I may be doing wrong in solving this specific tension ...
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5k views

Is it possible to find out the distance traveled by a car if the force applied on it is given?

Say you have car which produces $F$ amount of force which is transferred to the wheels directly. Now assuming that there is air friction which is causing a retarding force proportional to the ...
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140 views

How can one know if a theory allow action at a distance effects or not?

1-In general, if a theory has action at a distance effects, where can that appear exactly in the theory? 2-Does it appear in the dynamical law of the theory? (does it appear in Newton's 2nd law? ...
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623 views

Relation between linear momentum and translational kinetic energy

The momentum $m v$ of a particle is formally the same as the derivative its translational kinetic energy $\frac{1}{2} m v^2$ with respect to $v$. Similarly the angular momentum $I \omega$ is the ...
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899 views

Motion of a rod struck at one end

Imagine a strong metal rod of uniform density and thickness floating in a weightless environment. Imagine it lies on an X-Y plane, with one end (A) lying at 0,0, and the other end (B) at 0,1. Then it ...
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Calculating mass of object by lifting edge

Assuming a solid rectangular plate, hinged along one edge. How does one calculate the mass of the plate if the force necessary to lift the opposite edge is known?
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Centripetal force of a rotating rigid body?

Consider someone pushing a roundabout in a playground. Initially the roundabout is stationary, but when it is pushed, it rotates with increasing rotational speed. The force of the push is ...
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268 views

Can conservation of energy be applied if trajectory is not smooth?

In this video http://www.khanacademy.org/video/conservation-of-energy?playlist=Physics Khan academy explains conservation of energy for a falling object. He looks at an object falling ...
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1answer
219 views

Spring oscillations and waves

Consider a block of mass $m$ attached to a spring. Let it oscillate at a frequency $f$. Now each part of the spring is in SHM. so this means a wave is propagating through this spring.bCan this wave be ...
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68 views

non constant acceleration problem [on hold]

The acceleration of an arrow from a bow falls from $6000m/s^2$ to zero when it leaves the bow after travelling a distance $x=0.75m$. Assuming that this acceleration can be expressed by the linear ...
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48 views

How can a pulley work?

Assuming $g=10m/s^2$, the $2M$ mass would exert a $20M$ force on $M$, and by newton's third law, the $M$ mass would exert an equal and opposite force of $20M$ on the $2M$ mass. How would this ...
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1answer
56 views

How I think about rolling [closed]

Below, I have written how I think about rolling. I wish to know if my idea as to how it works is correct. Consider a rigid ball on a plane which has considerable friction. If you push the ball ...
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1answer
35 views

Component of Component of a vector [duplicate]

NOTE : By perpendicular component of $\vec{F}$, I mean a vector which is a component of $\vec{F}$, but perpendicular to it. In the image above, the red vectors are a possible set of rectangular ...
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95 views

How to explain the force applied on this object? [closed]

Sorry for posting such a simple problem but I'm having trouble understanding this concept. In the picture below, we have a force, $ \vec F_{app}$ acting on two objects, A and B. Mass of block A: $ ...
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1answer
15 views

Kinetic Energy in the Center of Mass Frame

Given two bodies moving along a line, I can find the velocity of the center of mass frame. Taking the time derivative of the Galilean transformation I get $v'=v-v_{cm}$ By definition, the total ...
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47 views

Mass required to prevent sign falling over with a set wind load - activity stations for disabled children

I'm currently working on my thesis and I'm stuck on a question. I'm designing activity stations for disabled children to be used for equine therapy. The stand is 9ft tall and I've calculated the the ...
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Is Keplers First Law a consequence of the conservation of angular momentum?

It would seem that once you have deduced that the angular momentum is conserved then you can deduce: $r^2\dot{\theta}=h$ is constant Combining this with the radial equation of motion then yeilds a ...
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1answer
45 views

Change in energy during orbital decay

Suppose we have a planet orbiting a star and the planet radiates away some amount of energy $\Delta E$. I want to find by how much the orbit decays (i.e the change in orbital radius). One way to do ...
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1answer
38 views

Will the Earth ever show synchronous rotation? Why and when?

In this answer to the question "why does the moon have the same rotation and revolution periods?", we read: The mass and speed of rotation of the Earth influence the moon in that some of its ...
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1answer
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Motion under gravitational forces

In a system of particles, can a particle be considered to be attracted to the combined center of mass of the other particles if the Newton's universal law of gravitation is used (the inverse square ...
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54 views

Question about Kinetic Energy and Force acting on a body

Below is the graph of a body that rests on a friction-less flat surface. On this body force F is applied and it's value is being depicted in the graph below. We can see that the body moves from point ...
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Why do the masses in an Atwood's machine move?

The masses you see on the following picture are $m_1=8$kg and $m_2=12$kg. Also the coefficient of friction between $m_2$ and the floor is $0.25$. What i'm concerned with is that although $m_2 ...
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66 views

Confusion with Newton’s third law

Suppose i push a box with my hand which has a mass=1kg. I apply a force of 2 newtons and it will accelerate at 2m/s^2. But, according to the third law, the box applies a force on me, which is also ...
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1answer
54 views

Can a planet's orbit around a star be simulated? [closed]

Say I know all parameters like density, size, rotational velocity of a planet, could I predict its orbit around a star where I also know parameters of it? I want to design a simple model of the solar ...
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189 views

At What Point Does Mass Cease to Matter?

I know very little about physics so I naturally have a lot of simple minded questions. Assuming I am piloting a rocket and want to obtain the fastest speed possible. At what point does mass more ...
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2answers
90 views

Why can we assume, when dealing with tension, that the mass of a rope is $0$ but still assume that there are forces on it?

I started studying tension and I can't understand the following concept: If I have two objects $A,B$ collegated by a rope, where $A$ applies a certain force $\vec{F}$ on it, I would have that the ...
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72 views

Violation of Newton's third law

consider the following situation shown in the diagram below.A huge wall of mass M is moving to the left due to a constant force of 100N. Now suppose a man of mass m applies a force of 20N to the ...
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1answer
59 views

Rotational equilibrium Paradox

A block of mass M and height h is moving on a rough surface of coifficent of friction 0.5 .The block is moving with a velocity v at some instant. if we balance the torque due to frictional force and ...
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107 views

Force required to send ball in set trajectory

If I have a desired 2D trajectory where I know the desired speed of my ball and desired path, and a ball that starts at (x=0,y=0), how can I calculate the required force / point at which the force ...
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2answers
45 views

Tension at topmost point of a vertical circle

I read that for a body to move in a vertical circle, the minimum tension needed is 0 at the topmost point. Can someone explain to me what it means to have positive or negative tension on top. I'm not ...
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110 views

Why do objects move when you apply a force that's equal in magnitude to the friction? [duplicate]

If the friction on an object is 200 N and you apply 200 N, it seems, the forces should immediately cancel each other out since the friction and your applied force go in opposite directions, leaving ...
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1answer
43 views

Alternative method for pulley system not working

We have two a pulley system with two masses of 2kg and 3kg on two ends of a massless string. At the end of 5 seconds, the string breaks. How far up did the 2kg block move? Here's what I have tried:- ...
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3answers
50 views

The formula for the kinetic friction on inclined surface

I'm confused about the formula for the force of friction on inclined surface. It says that $f$ (force of friction) = $\mu N$ (where $\mu$ is the coefficient of the friction). Is: $$f = ...
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3answers
79 views

Prove that the spacetime interval is not invariant under Galilean transformations [closed]

The spacetime interval $(\Delta s)^2 = (\Delta x)^2 + (\Delta y)^2 + (\Delta z)^2 - c^2(\Delta t)^2$ is invariant under the Lorentz transformation and this isn't the case for the Galilean ...
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1answer
129 views

How are the watt-second, the newton-meter and the joule different?

The joule is $\mathrm{kg\,\ m^2/s^2}$ right? The watt-second is $\mathrm{J/s} \times \mathrm{s}$ thus $\mathrm{J}$. The newton-meter is $\mathrm{kg \,\ m/s^2} \times \mathrm{m}$ thus $\mathrm{kg \,\ ...
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1answer
90 views

Whether a large or a small ball fall faster in the air?

Given a ball falling under gravity is subjected to air resistance, after performing a differential to the drag equation, I get: $$g-Z(v^2)/r = a = v',$$ (where $Z$ is a constant.) How can I know ...
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1answer
376 views

Center of mass (COM) of a uniform quarter disk [closed]

I was trying to calculate the coordinates of the COM for a uniform quarter disk. By symmetry, it must lie on the angular bisector of the central angle. Also, $A=\frac{\pi R^2}{4}$, thus ...
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1answer
80 views

When to use a whole vector approach vs an energy approach?

My professor has just introduced two new ways to solve projectile motions. One approach involve using trigonometry and vectors and the other involves using the idea of conservation of energy. My ...
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2answers
230 views

Hooke's Law and Simple Harmonic Motion

Can anyone explain how the following formula is derived and what it means? $$x'' = -n^2x $$ I was reading through my high school physics textbook and I stumbled upon a section on Hooke's Law. It says ...
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Rocket velocity during fuel burn [closed]

I know the formula for the velocity of a rocket after the on board fuel has been used up: $$ \Delta v = v_{ex} \ln\left( \frac{m_i}{m_e} \right) - gt $$ where: $v_{ex}$ is the exhaust velocity ...
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What happens to the kinetic energy of a dropped ball when it comes to rest on the ground?

If we want to drop a ball from a height, we calculated that potential energy at bottom is zero and we say it is converted into kinetic energy. At that movement, if it is a kind of sand, we find it ...
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Can the anti-torque of a motor be used to spin a space vehicle about it's axis?

Imagine an electric motor together with its power supply in space. What exactly will happen to it if it is suddenly powered? Will it spin about its axis, or it will experience no motion relative to an ...
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1answer
73 views

Does a laser beam generate an equal and opposite force

If I hold a laser pointer and press the trigger does the emission of the beam generate kick-back in the opposite direction through conservation of momentum. I understand it would be tiny, so my ...
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Acceleration of a particle moving along a straight line

If a particle moves along a straight line, then can we say that the acceleration should be zero? and if not, then why? If the equation of the motion is linear, then the velocity is constant and if ...