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 doesn't an orbiting body keep accelerating?

As a physics newbie I'm trying to get a grip on basic orbital mechanics. I think I'm beginning to get grasp on how bodies interact with each other. When a body approaches another body it accelerates ...
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1answer
245 views

Naming vectors in free body diagrams

Is there a convention for naming the vectors? Suppose there is a box on a table. I'm going to draw the forces acting on the box. So I focus on the box and ignore forces acting on the table, the ...
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1answer
972 views

Moment of Inertia of a sector of a circle [closed]

I am trying to find the moment of intia about its centre of a sector of a circle of radius $a$, mass $m$ and angle $\pi/3$. I have found the answer it is $\frac{1}{2}ma^2$ but originally tried a ...
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1answer
524 views

Kicking a soccer ball

I wonder which type of kicking may cause the ball to go a larger distance? One way is kicking the ball when it is at rest and another is kicking a moving ball in the opposite direction. If the ball ...
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3answers
304 views

Pendulum (highschool)

I have a question concerning pendulum. On our physics lessons we built simple pendulum consisting of weight and a thread ($\ell=0.31$ m). We tried to calculate $g$ from the well known formula $$T_m ...
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1answer
98 views

Minimize initial velocity of projectile to arbitrary point

I'm supposed to shoot a projectile from the origin to a point $(x_0 , y_0)$ with minimal initial velocity $v_0$. (no air resistance; regular gravity) The flight time should be $T=\frac{x_0}{v_x}$. ...
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2k views

Derivation of Euler's equations for rigid body rotation

Sorry for using this image, but I thought this was the most convenient way of asking this question. Please zoom in. I do not understand from the line, "Now, in the body frame $T = (T_{x'}, T_{y'}, ...
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3answers
3k views

How do birds generate thrust?

I have been watching this video carefully and I want to know how the wings of birds generate thrust. This is because the wings are more or less flapping up and down --- generating the lift. But I do ...
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4answers
157 views

Newtonian physics vs Special relativity - what is the most “relative”?

This might be a question purely of words and the meaning of them but isn't Newtonian physics more "relative" than Einstein's Special relativity? Newtonian physics predicts that laws of momentum & ...
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1answer
53 views

Obtain rate as a function of position for a force $F=-b\left( \frac{\partial x}{\partial t} \right)^{2}$

I have trouble getting the speed as a function of position for a force of the form: $$F=-b\left( \frac{\partial x}{\partial t} \right)^{2}$$ I had thought to use Newton's second law, so: ...
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374 views

Law of attraction

Could you please explain that since we know Newton's law of Universal Gravitation says all masses attract each other. Thus, we humans should be attracted as well or any other daily life objects. Why ...
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2answers
5k views

Direction of force of friction?

I know that friction opposes the direction of the velocity, but the problem is when I don't know what the direction of the velocity is. When I'm drawing a FBD for complex systems with ramps and ...
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184 views

Solids: is energy expended in some fashion by, say, a table to keep the top from sinking down against gravity?

A friend and I were discussing this, and couldn't decide. Since it takes energy to physically raise something up above the planet's surface, does it continue to require energy in order to keep it ...
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2answers
496 views

Does light have mass/weight?

If I plug in my memory stick/USB into my laptop and load it up with documents etc. will its mass/weight increase?
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3answers
312 views

Why does centre of mass of ice-container system shift in absence of any net external force?

Consider a cube of ice in a flat based container(the base is very broad).The temperature of the system is at first fixed at a minus Celsius temperature, but then the system is left on a table with the ...
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2answers
1k views

Increase in velocity by loss of mass? [closed]

A trolley of mass 300kg carrying a sand bag of 25kg is moving uniformly with speed of 27km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at ...
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3answers
750 views

What stops the car?

Centre of mass of a system cannot change its state of motion, unless there is an external force acting on it. Yet the internal force of brakes can bring a car to rest. Then what stops the car?
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355 views

Tension in vertical circular motion

In vertical circular motion we conserve energy for calculating velocities at a point (if initial velocity given). But, energy can only be conserved when forces are conservative. Tension is not a ...
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1answer
854 views

Moment of Inertia and Rotational Dynamics? [closed]

I'm having problems with the intuition behind the Parallel axis theorem and the Perpendicular axis theorem. I'm self studying Mechanics for the British Curriculum but, the book I've is missing the ...
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1answer
2k views

Are principle of Conservation of energy and principle of conservation of momentum consequences of Newton's laws?

It is known that principle of Conservation of momentum and principle of conservation of energy are two fundamental principles of physics.But in RP Feynman's Lectures of physics, in the chapter of ...
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18k views

Finding the drag force (Air resistance force) for accelerated ball?

As you know if I want to find the force for an accelerated object I will use the law $F_o=ma$ so I can get the affecting force of it. But there is another force affecting against the object. It's the ...
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2answers
2k views

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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3answers
755 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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2answers
239 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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1answer
2k views

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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2answers
341 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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2k views

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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1answer
2k views

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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3answers
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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2answers
933 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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1answer
2k views

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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269 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
220 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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3answers
51 views

Resonant Frequency of 2 mass spring system

So the question goes if I has a spring with spring constant $k$ and two masses attached to this spring (one on either side) what is the resonant frequency of the system in terms of $m$ and $k$? ...
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43 views

Calculate gravity between two points

I am trying to build a simulation of gravity in LibGDX using Bullet physics. To simplify it, I just want to apply a force on some body towered a (0,0,0) point. I got my body mass and it's location ...
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2answers
69 views

Does Buoyant Force always act upwards?

I have always used buoyant force as acting upwards in any problem related to fluid mechanics that I have solved. Also, if we push a mug down a bucket of water. It rises up, always, not diagonally even ...
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1answer
75 views

Where is the mistake in the following rationament [duplicate]

Well... kind of hard to translate in English so bare with me :). Let's consider a wheel that spins in the void. Each point of the wheel has the speed $v = ω r$. That means that for any $ω$, there is ...
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1answer
39 views

Conflicting answers gained from different equations

First time posting I hope this is the place. if someone could help me sort out formatting for the equations that would be nice "As a result of being hit from behind by a toy truck, a 50g toy car ...
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2answers
52 views

Water compressibility and pressure

I am so sorry if I am missing something, but for some reason I am very confused on how water can have pressure but not be compressible. If pressure is created by individual molecules bumping into the ...
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3answers
92 views

What is the physical meaning of reduced mass?

If we stick two block masses by a string and pass it over a pully and let the blocks free then mathematically we can obtain that the whole weight on the pully is more if the blocks are kept at rest, ...
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2answers
83 views

non constant acceleration problem [closed]

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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3answers
52 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
57 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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2answers
68 views

How does rocket thrust work?

I can't seem to find a specific answer to this anywhere. I understand that in a rocket there is a chemical reaction that causes gas particles to leave the rocket at high velocity. By Newton's third ...
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1answer
41 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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3answers
103 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
16 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 ...