Tagged Questions

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.

learn more… | top users | synonyms (3)

4
votes
1answer
786 views

Combining Proportions to get Newton's Law of Universal Gravitation

I've read a little on the history of Newton's Law of Gravitation and noticed that the formula can be separated into 3 distinct parts that lead to the end result of $F_g = G \frac{m_1 m_2}{r^2}$; the ...
3
votes
3answers
5k views

Angles on swing sets

I'm building a swing set for my children. All of the designs I've seen involve building two A-frames and connecting them at the top with a crossbar/beam from which hang the swings. The A-frames are ...
2
votes
5answers
3k views

Why Gravity attracts all objects with the same speed?

Why Gravity attracts all objects with the same speed? Is this question was solved? What is the exact answer?
0
votes
2answers
129 views

Showing $ m\int \frac{d\textbf{v}}{dt} \dot \normalsize \textbf{v}dt = \frac{m}{2}\int \frac{d(v^2)}{dt}{}dt$

Can someone please explain how this equation is valid, using intermediate steps if available? $$ m\int \frac{d\textbf{v}}{dt} \dot \normalsize \textbf{v}dt = \frac{m}{2}\int \frac{d(v^2)}{dt}{}dt$$ ...
1
vote
1answer
159 views

Determining Orbital Velocity

Is there any way to determine the orbital velocity of a point around another stationary point, if I don't know the mass of either of the points but know the force that gravity exerts and the distance ...
1
vote
1answer
287 views

What controls whether a ball will skid or roll?

A billard ball is struck with a cue. The line of action of the applied impulse is horizontal and passes through the center of the ball. The initial velocity $v_0$ of the ball, its radius $R$, its mass ...
2
votes
3answers
414 views

Can an object move without relying upon Newtons third law?

Pretty much everything we do appears to boil down to practice of Newton's Third law. Even this rug I'm seated upon relies upon reaction from the floor to keep me seated. Amongst others the same ...
5
votes
3answers
5k views

Direction of rotation of a celing fan

From Constellation Energy Quick energy efficiency tip: To stay cool and manage your energy at the same time, use ceiling fans to create a “wind chill” in rooms you are using. The wind chill ...
0
votes
2answers
610 views

From where does the force/energy of action-reaction comes from? (Newton's Third Law of Motion)

I was wondering, from where does the opposite force and thus energy comes from when we apply force. For example, lets say there are two persons (P1 and P2) on the universe, and no force is applied to ...
0
votes
4answers
300 views

Is this a valid understanding of Newtonian mechanics?

This is a conceptual understanding of Newtonian mechanics. What the laws mean, how we know they're true, etc. I'm looking for criticism. I know this is really border line on the "don't ask questions ...
1
vote
2answers
63 views

Can you launch an item farther by slamming into it or accelerating it along a length

I am trying to desgin a little penny balista toy (built with a 3d printer). The short description is that there is a track with a mass ("hammer") that slides along it. There is a stack of pennies in ...
3
votes
1answer
612 views

Acceleration of a Free-Falling System with Center-of-Mass Change

A thought experiment has been bothering me. Assume an enclosed box free-falling in a constant gravity field. The box contains a person and a bowling ball at the top end. The person throws the bowling ...
3
votes
1answer
577 views

Glass - paper: Stevin's Law

In my understanding the well-known experiment of the glass full of water in equilibrium with a piece of paper, the atmospheric pressure acts on a small layer inside the glass (on the top) and under ...
0
votes
1answer
429 views

Is my understanding of the mechanics of skidding correct?

I'm trying to understand the mechanics which determine if a car making a turn will skid. Are the following correct or incorrect: A vehicle making a turn will skid unless the centripetal force is ...
0
votes
3answers
331 views

How to imagine the following power and torque?

I can roughly feel a force of 10 newton only by considering the weight of 1 kilogram object. How to imagine the following measurements? Maximum horsepower 16 hp @ 9,500 RPM Maximum torque ...
0
votes
2answers
132 views

Really basic mechanics and Galilean Relativity question

Consider two solid objects: A and B. System 1: A <----- B 10m/s System 2: A -----> B 10m/s ...
4
votes
2answers
1k views

What causes a force field to be “nonconservative?”

A conservative force field is one in which all that matters is that a particle goes from point A to point B. The time (or otherwise) path involved makes no difference. Most force fields in physics ...
1
vote
1answer
230 views

How do I factor in multiple forces into these Newtonian mechanics equations?

Say a person is walking along. He then jumps. The person weighs $25$kg (irrelevant?). Just after jumping, his velocity is 5m/s (positive is taken as up). Gravity is taken as ...
1
vote
1answer
328 views

Why ballasted gliders fly faster

The fact: Gliders have ballast tanks that can be filled with water. The addition of ballast increases weight, and this allows the glider to fly at faster airspeeds while maintaining the same glide ...
1
vote
3answers
2k views

What is the principle behind centrifugation?

What is the principle behind centrifugation? I understand the idea that you spin something around the centripetal force will cause an apparent force on the spinning system. However I don't quite ...
9
votes
2answers
2k views

Might a planet perform figure-8 orbits around two stars?

Might a planet perform figure-8 orbits around two stars? I'm thinking that if the two stars were equal mass (and not orbiting each other) then a planet that were to go right between them would ...
1
vote
3answers
127 views

Estimate quarter mile time

I need to estimate a drag race quarter mile time given the car's weight, bhp and preferably the drive (FWD, RWD, 4WD). I know $v(t) = ds/dt$ and $a(t) = dv/dt = d^2s/dt^2$, but how can I get the ...
1
vote
3answers
1k views

Why airplanes fly: the final truth

The questions about the reasons the aircraft fly are frequent among scientist, since the high school until now, even if I work on the other side of fluid mysterious world (the Low Reynolds numbers ...
1
vote
2answers
364 views

The two-body problem: What is force between them?

Two bodies with similar/different mass orbiting around a common barycenter. What is force between them, where $F_{12}$ is the force on mass 1 due to its interactions with mass 2 and $F_{21}$ is the ...
2
votes
1answer
580 views

When does centripetal force cause constant circular motion?

As far as I know, if an object has a speed $s$ and a force is applied to it which generates an acceleration of $s^2/r$, then the object will start moving in a circle of radius $r$. Also, as far as I ...
2
votes
1answer
258 views

Snooker/billiards cueing

I understand the 2 body dynamics very well, but I can't see how the professionals apply their chalked cue and hit the way they do. As a few for instances: How much does the chalk come into play in ...
2
votes
1answer
554 views

Circular Motion Equation Derivation

I am given a series of three equations, which someone has used to determine the Tension force in a rope swing: $$mgh=1/2mv^2$$ $$T-mg=\frac{mv^2}{r}$$ $$T=3mg=1764N$$ I am asked to exaplain the steps ...
1
vote
1answer
326 views

What is the typical orbital life of an artificial satellite?

The orbit of satellites around Earth eventually decays, or so I read. This is typically caused either by atmospheric drag, or by tides. I would assume most satellites have a limited service life in ...
6
votes
3answers
576 views

Why didn't Newton just propose the 2nd Law and leave it at that?

Why didn't Newton just propose the 2nd Law ($F=\dot{p}$) and leave it at that? The 2nd Law implicitly contains the first, doesn't it? If so, it seems he wasn't following his own Rule #1 of Book 3 of ...
2
votes
3answers
961 views
1
vote
1answer
131 views

Gravitation and equilibrium (…and similar problems) [closed]

One problem that I'm having trouble with (as opposed to the other): The Messenger is a probe that orbits Mercury $700 \rm km$ from the surface. What is the tangential velocity it should be ...
0
votes
1answer
137 views

Storing light energy as potential kinetic to drive an electric generator [closed]

I would like to lift a 10 ton mass (crate of rocks) to a height of about 80 feet using a small 24 volt electric motor powered by a 16 square foot photovoltaic panel. Then I would like to collect the ...
2
votes
1answer
561 views

Analogy between magnetic bottle and Van Allen's radiation belt

A magnetic bottle is an arrangement that permits to confine charged particles. Here you can find a review for charged particle rotating in a magnetic field and at the bottom of the page a description ...
0
votes
2answers
4k views

Circular motion period equation

The equation, $$ a_c=\frac{4\pi^2r}{T^2} $$ Can be expressed as: $$ F_c=\frac{m4\pi^2r}{T^2} $$ I am confused as to how to arrive at this second equation, and the relationship between these two ...
3
votes
2answers
516 views

At what g is terminal velocity not terminal?

How weak would gravity need to be in order for a human to reliably survive the terminal velocity of falling through air? (Context: watching scifi on a space station with a variety of artificial ...
1
vote
2answers
175 views

Unexpected potential energy increase during Tic-Tac drop

I dropped a Tic-Tac: (no worries, it happened before), and I noticed as it bounced on the floor that it would first jump 20 cm high, and at the next bounce for instance 50 cm high. Shouldn't it ...
5
votes
1answer
330 views

What in Newtons three laws of motion original to himself and not a paraphrasing of his predecssors

The three laws are: First law: The velocity of a body remains constant unless the body is acted upon by an external force. Second law: The acceleration a of a body is parallel[disambiguation needed ...
1
vote
1answer
494 views

Relation between 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 ...
2
votes
2answers
3k views

Determine the acceleration and angular acceleration of a disc

The question is: A 90kg disc is floating in a frictionless vacuum. A 150N force is applied to the outer rim of the disc. The disc has a radius of 0.25m and a radius of gyration of 0.16m. What ...
2
votes
2answers
1k views

Why is the center-of-mass of 2 bodies at the focus of their elliptical orbits?

Why is the center-of-mass of 2 bodies (which interact only via Newtonian gravity) located at a focus of each of the elliptical orbits? I know that when there are no external forces, the center of ...
4
votes
2answers
491 views

How much thrust would be needed to turn a hobbyist weather balloon into a deep space probe?

I was reading the article Weather Balloon Space Probes that says you can put your own balloon probe at 65,000 ft temporarily. Is it even remotely possible to raise the probe high enough using ...
4
votes
5answers
763 views

Does Newtonian mechanics predict the bending of the course of light by objects with mass?

$F=Gm_1m_2/d^2$ $F=ma$ $a_g=Gm_{other}/d^2$ In Newtonian mechanics, the acceleration of object A toward object B is not dependent on the mass of object A but on the mass of object B and the ...
2
votes
1answer
538 views

How does Lunar Orbit Injection (LOI) work?

Just what the title states. I read that LOI was used by the Apollo program (and possibly others) to achieve escape velocity. How does it work? Is it merely a matter of centrifugal/centripetal force?
7
votes
5answers
3k views

How long must escape velocity be maintained?

Escape velocity from Earth's surface is 11.2 Kilometres/second How long would one need to maintain this escape velocity to actually escape Earth's gravitational pull? Must this 11.2 km/s velocity ...
1
vote
0answers
161 views

Hooke's Law and the shape of coils

I've learned in school that the force in a coil is $F=kx$, linear on how much the coil is stretched. Two questions: Is it always linear for every shape of a coil? Does it remain linear if we ...
2
votes
3answers
3k views

Proving angular momentum is conserved for a particle moving in a central force field $\vec F =\phi(r) \vec r$

A problem I am trying to work out is as follows: A particle moves in a force field given by $\vec F =\phi(r) \vec r$. Prove that the angular momentum of the particle about the origin is constant. ...
2
votes
1answer
368 views

What is the Lie algebra of the Galilean group and what is the structure of it?

I read Freeman Dyson's article Missed Opportunities, in which he talked about the mathematical attractiveness of the Lorenz group compared to the Galilean group. I am reading Florian Scheck's book on ...
3
votes
3answers
3k views

Does friction decrease as objects move faster against each other?

I was told that the faster two objects move against each other, the less the friction between them would be… compared to if they were moving slower. In physics class, we always use the coefficient of ...
0
votes
2answers
203 views

Aerodynamic drag on a cannonball?

I'm trying to build a ballistics simulation where I shoot a cannonball. I want to allow for drag and am trying to work out the math to do so. I can work the drag out using $F = C_d\times S\times ...
1
vote
1answer
91 views

How do we describe the relationship of balloon size and related lift?

We know that hydrogen and helium are lighter that air. Therefore it is certain that they would create a lifting force when enclosed in a balloon. How do we describe the relationship of balloon size ...