# 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.

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### Is the center of mass of an object just a convention?

I am currently studying moments. The concepts are fairly obvious, but there is one thing I don't understand: the concept of center of mass. Why do we consider that the weight of a uniform object is ...
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### Force of tension on both sides of one string- 2 questions

Here's something I want to ask you guys about: Many times downward N1 and N2 are ignored in exercises. Why? If forces of tension are balanced by each other, why won't objects just fall? Cheers ...
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### Moving a block up a ramp

Would this be a valid way to approach this? Find the force needed to push a block of mass 5kg to the top of a ramp whose length is 1m and makes a $30^\circ$ angle with the ground. W_{grav} = ...
92 views

### Do all thing move against gravity with -9.8 meter per second squared acceleration?

If I throw a ball to height h above the earth's surface and then shoot a bullet that reaches the same height but would there be same quantity of acceleration produced in both?
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### Using formula for work with distance of 0m [duplicate]

Consider this: Wind is pushing a huge rock towards me at with massive force at 2m/s. I push against the rock at equal force so the rock stays still. I am clearly "working" very hard, using a lot of ...
159 views

### Calculate damping constant / coefficient

I am trying to graphically simulate a series of springs in 2D. Now one of the forces I am stuck with calculating is the damping force. The given formula is $F = -k_d v$. I know that $v$ is the ...
353 views

### What is the meaning of the negative sign in $W = -\Delta U$?

What is the meaning of the negative sign in $W = -\Delta U$ ? As far as I understand, $W = -\Delta U = -(U_f - U_i) = U_i - U_f$. While $U_i$ is the initial potential energy (before applying the ...
461 views

### A conical pendulum. A textbook claims one can start the circular motion in an unintuitive way

A textbook claims that if you hang a mass from a string that's attached to a rod (so that the string is parallel with the vertical axis) and you spin the rod fast enough, you can put the mass into ...
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### Why oobleck does not obey Newtonian dynamics? [duplicate]

In the following post we can see that some guys are walking on Non-Newtonian fluids. As far as I know that, we can not predict the exact amount of strain if we predict some forces. therefore the curve ...
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### Who is moving and with who's relation?

What if we are in a cube of 3×3 m  which is further enclosed in a sphere of radius 50 m? And the sphere start to rotate on its own axis would we experience force? If not then what happens if there is ...
194 views

### Imposing symmetries on asymmetrical dynamic systems

Let us say we have a one dimensional system of masses connected by springs. All the masses are equal and the springs alternate with spring constants of $k$ and $6k$. The appropriate way to analyze ...
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### What is the relationship between the Young's modulus of a material and the elasticity of a free fall collision

I'm coding a 2D physics simulator based around the Newtonian physics principles with some alterations due to computation limits and I am at the stage of creating a collision event between a planetary ...
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### What happens when a high speed motor tries to drive a heavy car? High torque?

I'm trying to figure out what would happen if a really high speed motor - which has enough power to drive a car, but very high RPM & very low torque - tries to move a car. Does it get stuck ...
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### why is there an 'equal' and opposite reaction if the force depends on the momentum?

If you have a large mass and a small mass that collide, the large mass reacts according the smaller mass's momentum and vise versa. For it to be consider 'equal' doesn't that mean they have to feel ...
176 views

### What made Kepler think that orbits are not circular which came to be elliptical?

Kepler formulated his laws in a sort of time where human began to believe in heliocentric universe and telescope was not yet invented/ discovered. So what made Kepler think that orbits aren't ...
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### How velocity progresses over time with a non-constant acceleration? [closed]

A $0.25\text{ kg}$ sphere of radius equal to $0.07\text{ meters}$ is dropped from rest from the top of a building. Granted that it will not hit the ground before, when and after what distance ...
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### Kepler's laws: show the planet always stays in the same plane？

I know angular momentum $L=q \times p$ is conserved, where $p=L_{\dot q}$ is linear momentum. How to apply this to a planet orbiting the star, described by the position vector $q$ relative to the ...
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### What is causing the normal force in circular motion?

In the picture, at point 2 (the bottom of the ramp) the normal force of the object has a greater magnitude than weight. I understand that the normal force has to be greater than the weight since the ...
1k views

### Tricky conceptual question: ball sliding and rolling down incline [closed]

We all are familiar with the classic ball rolling down the incline exercise in rotational dynamics. Here is quite a tricky conceptual problem: You have an incline of fixed height, but the angle ...
92 views

### Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
239 views

### Air Drag in orbit

Artificial satellites don't orbit the earth forever. Eventually the Earth's atmosphere, thin as it may be up there, will bring them down. But did you know the linear speed of a satellite in a near ...
33 views

### Newtons 2nd law and longitudibal dynamics of bicycle

When a bicycle (of gross vehicle mass $m$) accelerates ($a$) forward, such that both the wheels are in pure rolling (no slipping), then: static friction ($f_{s1}$) acts on the front wheel backwards, ...
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### Writing collision equations with the help of coefficient of resistitution

Suppose we have a frictionless surface and a small particle of mass $m$ which collides with velocity of $V$ with stationary particle of $2m$ elastically. I know how to deal with this simple problem ...
156 views

### Air resistance force [closed]

How do I find the air resistance force and the maximum air resistance force when all I'm given is the mass, terminal velocity, and I know it's falling in quite air? I found a formula online but it ...
2k views

### How could a cord withstand a force greater than its breaking strength?

How could a 100 N object be lowered from a roof using a cord with a breaking strength of 80 N without breaking the cord?? My attempt to answer this question is that we could use a counter weight. But ...
2k views

### Why does it take a projectile as long to get to its apex as it does to hit the ground?

I was once asked the following question by a student I was tutoring; and I was stumped by it: When one throws a stone why does it take the same amount of time for a stone to rise to its peak and then ...
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### Normal force for car banking turn vs object sliding down slope

When describing an object sliding down a slope, we say that the normal force is less than the weight of the object, and that the vector weight minus the normal force equals the force with which the ...
38 views

### weightlessness and forces conceptional question

I am currently learning about forces and newton's laws of motion. I have a question in my book which I don't understand though... Here it is: (note: I dont want the answer I just want to understand ...
195 views

### When do we assume that a rope has different tensions in different places?

Working a problem with 2 pulleys and masses in class this week the professor at one point assumed that the tension on the two sides of a pulley would be different. Every other time we've done a ...
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### Can energy be extracted indefinitely from a mass dipole/mass negative mass pair in perpetual motion?

Some days ago I have read this short piece of article by Hammond which caused me to revisit the theoretical properties of negative mass. It is known that a pair consists of ordinary mass and negative ...
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### Conservation of energy, and Newtonian physics that does not fit

Here is a theoretical example where the energy into the system does not mach the energy output. There is no friction or air resistance. A sledge with a rocket engine attached to it is lying still on ...
191 views

### A simple pendulum

The idealized simple pendulum model (see the following figure) assumes that at every point of time the string to which the bob is attached exerts an equal and opposite force on the bob as does the ...
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### A twist on the leaning ladder problem

For the first part, I know will need to form moment equations and resolve horizontally and vertically. But how do I decide which position to take for the dog while I form moment equations?
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### Given the radius and angle of a frictionless banked curve, is it possible to find centripetal force?

A car is driving on a frictionless banked curve of radius 45 metres and 25 degrees. Is it possible to find centripetal force? If not possible, explain why.
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### Motion in the gravitational field along a trajectory [closed]

A point particle of mass $m$ is moving in the gravitational field along some trajectory which is described by the function $y=y(x)$, which is in a vertical plane and is continuous. Initial ...
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### On a banked turn, why isn't weight in x the centripetal force?

Why does the x component of the Normal force act as centripetal force in a banked turn and not the weight component in x? I know it may sound silly but please respond.
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### Two body problem with given start positions and velocities [duplicate]

I am trying to program a $n$-body problem simulation. To calculate the position and velocity after a time-step I want to split it in multiple 2 body problems. Now I am stuck, trying to find the ...
125 views

### Direction of friction vector when acceleration is zero

There is a box on a ramp, there is Wx that makes it fall, Tension that pulls it up the ramp (a rope) and Friction. The thing is, how can I determine the direction of the friction? For me, friction ...
221 views

### What happens to the velocity distribution during constructive interference?

Two pulses(one inverted & having velocity in the opposite direction) moving towards each other with same wavelength & amplitude after undergoing destructive interference do re-appear. Why? ...
170 views

### An object is placed on an inclined plane. Does it roll? [closed]

An object is placed on in inclined plane. There may or may not be friction, your choice. My question is, how do we figure out whether or not it rolls? For example a sphere rolls but a cube doesn't.
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### Pendulum forces in orbit

On Earth a pendulum is governed by a set of equations, relating the angle of the swing, the mass etc. However with a pendulum in orbit there is no fixed point (assume 2 masses attached via a string). ...
87 views

### Buoyancy force on a hung object [closed]

If an object is hung with a cord and it have been embedded in a fluid, then the buoyancy force will reduce the cord tension.What is the formula that governs this reduction ?.
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### Torsional spring and Euler angles

I have a question about the moments generated by torsional springs. Consider an inertial reference frame A and a body fixed reference frame B. The frames are connected by 3 rotational springs acting ...
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### Kinetics energy with different reference frame (a fighter plane shoots a bullet)?

Suppose a plane flies at 1km/s and shoots a 2kg projectile at 1km/s, so to the Earth the projectile flies at 2km/s with 2*2*2/2 = 4MJ. The same gun, when fixed on Earth, shoots the same 2kg ...
333 views

### Mass spring system, elongation of the spring [closed]

Is it possible to calculate the elongation of a spring with only the length of the spring, a spring constant and the mass that is attached to the spring?
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### What's wrong with this calculation of the center of mass of a triangle?

Find the center of mass $(x_G,y_G)$ of a homogeneous triangle of mass $m$. Divide it into infinitesimal rectangles of width $dy$, length $x$, mass $dm$ and area $dA$. We have $d A = x dy$ ...
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### Why in analysis of coupled oscillator, restoring force for uncoupled condition is taken in account?

If the pendulums were free & either one were displaced a small distance $x$, the restoring force would be $m{\omega_0}^2 x$. But in the present situation the coupling spring is stretched a ...
348 views

### Weight of an object at different angles [closed]

I'm trying to either find a calculator online or help with an equation to work out how much weight I'm lifting when I pick up my dirt bike off the floor [edit: when it's lying on it's side on the ...
The typical first application of Lagrange's equation is showing that it implies Newton's law for a particle whose Lagrangian is $L=\frac{1}{2}mv^2-V(x)$. Plugging this Lagrangian into Lagrange's ...