# Tagged Questions

This tag is for the classical concept of forces, i.e. the quantities causing an acceleration of a body. It expands to the strong/electroweak force only insofar as they act comparable to ‘classical’ forces. Use [tag:particle-physics] for decay channels due to forces and [tag:newtonian-mechanics] or ...

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### How do you find the tension in the real world? (Given a rope in a pulley system)

I'm well aware of the formula to calculate tension, however, given a real world situation where you have a closed pulley system. How do you measure the force (i.e., tension) required to pull on the ...
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### Problem of uncoupling a train

As a kid I have seen several movies, cartoon etc. in which usually one guy just uncouple (unplugs (?), dunno) the rest of a running train and then runs off with the locomotive at full speed and ...
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### Net force of the following? [closed]

The following objects are attached to one another and have difference force directions: Where is the direction of force? And What is the net force? I'm trying to calculate it using their angles, ...
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### Another condition of calculating work

Let's imagine that there is a box placed at the corner of a table, and I push it so that my applied force makes an angle of 30° from the table's surface. The box would move and, due to the effect ...
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### Why doesn't an object that collides with one that is at rest just do a 180?

Newton's third law says "for every action, there's an equal and opposite reaction." So why is it, say, that when a pool/billiards ball hits the wall of the table, the ball doesn't just turn around?
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### Why is the gravitational force $10^{38}$ times smaller than the strong nuclear force?

Also, why is the weak interaction force $10^7$ times smaller than the strong nuclear force?
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### Two boys pull a rope in the two edges with the force 50 N each. Will the rope rip if it can handle only a pull of 80 N? [closed]

I think we should make the sum the two forces 50+50=100 N and say it can't handle? Can you explain me using the 3rd Newton Law?
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### About Cell and its electric feild?

1.When we connect wire in a battery there is a electric field so current starts flowing? 2.Do electric field spreads everywhere except in wire? 3.Electric field starts from positive charge to ...
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### What happens when a force is not applied on the centre of the mass? [duplicate]

The answer to this question force applied not on the center of mass states that for a force applied not directly on the center of mass will have the same linear acceleration as one applied on the ...
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### Conservation of momentum when rain pours into a wagon

Suppose a wagon is moving at constant velocity on a friction-less surface, and rain begins to fill the wagon. The net force on the wagon is zero, so momentum is conserved; as the mass of the wagon ...
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### Tension of 2 massless springs joined together

A cable is formed by joining two massless springs with different spring constants. Spring A has constant k1. Spring B has constant k2. If mass M1 hangs from the cable, is the tension greater on spring ...
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### Understanding tension principles in a 2 pulley system [closed]

Trying to understand tensions in a 2 pulley rope system, where M1>M2. Is it true that T1>T2>T3?
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### Modeling external forces in Lagrangian dynamics

For example, consider a system with a block on a flat, frictionless surface. On one side is a spring connecting the block to a wall. On the other side, a person's hand is pushing the block towards the ...
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### Why don't we take force proportional to velocity? [duplicate]

When a Force is applied on a body at rest, it produces Acceleration which is equal to change in Velocity. But due to the Force, we see that the Velocity is increasing consequently. So why don't we ...
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### What forces cause the centripetal acceleration in circular motion on a merry-go-round?

Suppose you stand on a merry-go-round spinning at $f$ revolutions per second and you are $R$ meters from the center. What forces act on you? If you were tied to a rope like in Fig 2 you would follow ...
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### Torque and Pulleys [closed]

I have the solution to the problem below, however I approached the question differently than my professor and I do not understand why my answer is different. Can someone help explain where I'm going ...
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### Why is the relationship between velocity and radius curved, in circular motion?

We are supposed to graph velocity squared against period. My instructor specifically said: The gradient of this graph is acceleration and We should observe a trend of decreasing orbital velocities ...
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### How is the load handled between a car and it's wheel?

I know, based on research, that the load of a car is transmitted to the wheels by properly torquing the lug nuts. I'd like to verify this through science. Alas, it's been a decade since I last ...
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### What is the intuition behind “Net Work is Zero”?

I tried searching the answer to this all over the internet, but still cannot grasp this concept. So, when a book is being lifted, let's say $25 meters$ with a mass of $4kg$, with constant speed. I ...
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### Ratio of the magnitude of the normal force to the magnitude of the gravitational force? [closed]

I'm working through some practice problems in preparation for my physics final and ran into one that I'm not sure how to do. A mass is released from rest from the edge of a large hemispherical, ...
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### Force on a solid cylinder that is rolling on an accelerating block

Given: $m,R,I=mR^2/2, F,M$ and no traction between $B_2$ and the ground find $a_1, a_2$ (the accelerations of the CMs of $B_1$ and $B_2$ respectively).$B_1$ rolls on $B_2$ without sliding due to $T$.
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### What is the cause for the validity of Newton's third law?

What, specifically, causes newton's third law? For instance, if I push on a wall, why is it that I experience a force in the opposite direction? I seem to vaguely understand that is has something ...
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### Why does the water rise upwards when the bottle fall down with accleretion $>>g$?

When a medium-sized bottle filled with water quarterly falls from a height with acceleration $g$, the water remains calm. But when it falls with acceleration $>>g$, the water abruptly rises up ...
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### Ball flying towards me or me flying towards ball

Suppose a ball is flying towards me at a speed of 10m/s and that, on impact, I feel "x" amount of pain. If, instead, it was me flying towards the ball at the same speed, with all other conditions ...
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### Frictional force require to balance leaning sticks

Here is the question (from Morin's Introduction to Classical Mechanics book): One stick leans on another as shown in Fig. 2.21. A right angle is formed where they meet, and the right stick makes ...
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### Pendulum's motion

Consider a pendulum in it's balance point hanging from ceiling. It can swing in all the directions in the space. The pendulum can only swing in a sphere(the string can't bend). Now, is it possible to ...
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### Intuition and difference between centrifugal force & Coriolis force?

My book says that when a frame rotates uniformly, pseudo/fictitious force must be taken to count. This is centrifugal force. Also, while Googling, I found another pseudo force Coriolis force. ...
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When an object hangs from the ceiling, through a rope, the tension force acts upwards, against the force of gravity. However, when a boy pulls a wagon, the tension force acts in the direction he is ...
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### Inclined plane, circular motion and the friction

Suppose we have a cylinder on an inclined plane of mass $m$ and radius $R$ moving without sliding (so that $\varepsilon = a/R$). Why is the friction $F$ causing the circular motion sometimes lower ...
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### What is the basic reason behind buoyancy?

Yesterday my friends and I were solving this easy-looking question: A metal cube is placed in an empty vessel. When water is filled in the vessel so that the cube is completely immersed in the ...
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### Why do these two derivations of the formula for impulse contradict?

I was trying to derive $I = F\Delta T$ from $p = mv$. First I converted $v = at$: \begin{align} p &= mv \\ p &= m \times at \\ p &= ma \times t \\ p &= Ft \\ \Delta p &= F \...
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### Doesn't a box holding a vacuum weigh the same as a box full of air?

This was recently brought up, and I haven't been able to conclude a solid answer. Let's say we have two identical boxes (A and B...
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### The force acting on a plate of a parallel capacitor

How can you prove (using high-school-knowledge) that the force which acts on one plate of a parallel capacitor is equal $F = \frac{E \cdot Q}{2}$ Where $E = \frac{U}{d}$ is the magnitude of the ...
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### How to check if a system is in SHM in two spring systems?

I must determine if the system (a) is in SHM. I must arrive to the conclusion that there is a linear restoring force such that $a=-w^2x$. The solution's manual affirms that according to Newton's ...
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### Question about central force,and acceleration of the tangent velocity due to a radial velocity and angular momentum conservation

I am a bit confused, and I'll appreciate some help. Let's say that a particle is moving under the influence of a central force. Let's say that its initial velocity, has both: tangent component and ...
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### How Earth's Gravity is more powerful than its centrifugal force?

How Earth's Gravity more powerful than centrifugal force? The earth spins all the time but we are not holding onto something to avoid drifting off in space cause of the centrifugal force.
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### Does String Theory Predict more than Four Forces?

String theory literature tells us that ST predicts the four forces: weak, strong, EM, and gravity. What it fails to tell us is if that's all the forces it predicts. Might there be a fifth force that ...
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### Why isn't there a net force when two rods touch each other?

This is a problem from Beer and Johnston's Mechanics of Materials (Amazon link). There's a problem in which there are two rods of different material, area, and length. The rods are fixed to walls, ...
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### Energy loss through gravity and the law of conservation of energy

Since every object exerts a force of gravity on all objects around it, how can it lose so much energy at all times without ever stopping? If an object always loses energy from gravity, how does it ...
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### Prevent a box from tipping over: height of CG?

I'm on a problem that can be simplified in the following way: A box is placed on a horizontal plane, and is pinned to the ground on one side only such that it can tip over that side. Given a ...
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### Would “The Flash” be able to fly? [closed]

I'm addicted to the new TV program The Flash. In the last few episodes, the maximum speed required to "beat the bad guys" has been increasing. The most recent episode required him to run at Mach 1.3 (...
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### Waves and Newton's Third Law

I'm a really newbie in Physics trying to understand a bit about waves. Firstly, i'm using the Wikipedia's definition of wave , that is, as energy traveling through a medium/space without ...
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### Problems when a disc is rotating at extreme speeds (theory)?

I was wondering the problems that would occur (aside from mechanical friction), when a disc rotates at high angular velocity. Is centripetal force an issue if high torque is applied on a disc (massive ...
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### The principles of statics without force

I'm a student of civil engineering and now my course is covering the basics of statics, such as the equations of equilibrium, etc. Trying to get a better basis on the subject, I started to search on ...
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### Newton's third law and punching a glass or a feather

According to Newton's third law, action force equals reaction force in terms of magnitude. When I punch a glass, the glass punches me back. If I exert a greater force on the glass, it will break. ...
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### Why does a spring fixed to a wall have PE and not KE?

As many books,including mine (Principles of Physics by Resnick and Halliday) introduce, I also will present my example like this: Let there be a spring of negligible mass attached on one side ...
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### Calculating the force required to lift a weight with a screw

I am trying to learn physics by myself as I do not have a good teacher at school. I've been reading Feynman Lectures on Physics and I can't figure out how he found out this number. Here is an excerpt ...
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### Torque and Car parked on slope [closed]

I have a homework question in which a car of mass $M\ kg$ is parked on a hill inclined at $25^o$ The car is facing up the hill and I am told that the wheels are $3\ m$ apart and the centre of mass is ...