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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1answer
238 views

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 ...
5
votes
3answers
1k views

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 ...
1
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2answers
100 views

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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17answers
9k views

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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0answers
827 views

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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2answers
133 views

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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1answer
200 views

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 ...
-1
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1answer
111 views

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.
5
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2answers
143 views

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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2answers
56 views

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, ...
0
votes
1answer
117 views

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 ...
0
votes
2answers
565 views

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 ...
-2
votes
1answer
288 views

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 (...
4
votes
1answer
346 views

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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0answers
42 views

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 ...
2
votes
2answers
102 views

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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votes
6answers
2k views

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. ...
2
votes
4answers
418 views

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 ...
10
votes
2answers
5k views

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 ...
0
votes
1answer
632 views

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 ...
1
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1answer
50 views

Buoyant Force Issue

I don't understand why the buoyant force is equal to the weight of the displaced water for objects that are not "spheres of fluid." Why does the reasoning for fluid spheres hold for other objects?
-1
votes
1answer
48 views

2012 quo. no. 14 $F_{net} = ma$ [closed]

Please refer to #14 in this document Please help me solve this problem... I don't understand why a force (in the problem, T) even needs to be applied to keep the ball in equilibrium. There is no ...
1
vote
1answer
124 views

Disk and Ball on a smooth surface [closed]

A uniform disk of mass $\text{2m}$ and radius $\text{R}$ is placed freely on a smooth surface as shown in the figure. A particle of mass $\text{m}$ is connected to the circumference of the disc with a ...
0
votes
1answer
71 views

Problem on Inclined Forces [closed]

I am having trouble on one of my homework problems. The problem is What is the acceleration of the system if M1 is 5 kg and M2 is 4kg and the coefficient of friction between M1 and the table ...
0
votes
2answers
307 views

Possible solutions to the crown problem of Archimedes [closed]

My teacher was talking about the crown problem, possibly solved by Archimedes using skills about density, weight and other properties that he studied. In the original publication, by Vitruvius in a ...
2
votes
5answers
2k views

Relation between potential energy and forces

Can you also explain why can't we define potential energy corresponding to a non-conservative internal force? Non-conservative forces are those which don't depend on the initial and final states but ...
45
votes
5answers
7k views

Why is the Moon considered the major cause of tides, even though it is weaker than the Sun?

You have likely read in books that tides are mainly caused by the Moon. When the Moon is high in the sky, it pulls the water on the Earth upward and a high-tide happens. There is some similar effect ...
1
vote
3answers
2k views

Impulse and force in a karate chop, can we maximize force minimizing the time of impact?

I have heard that we can maximize the force by minimizing the time of impact in a punch. If that is true, the paradox is if we increase the time of contact with the same amount of force still we ...
3
votes
2answers
736 views

Validity of work-energy theorem in presence of non-conservative forces?

How can the work-energy theorem be valid in presence of non-conservative forces since conservation of energy is not there?
5
votes
3answers
994 views

What forces are at work in a loose ball bearing bicycle hub?

I've landed in a physics debate amongst bike mechanics. In a typical bicycle hub you have a simple bearing; the cups are set in the hub, the race (cone) threads onto the axel and there are just loose ...
2
votes
1answer
163 views

Elasticity of a body on which variable force is applied

Let us consider a rod of some cross sectional area $A$ and length $L$. At one end a longitudinal foce of 5x acts on the rod. At a distance of $\frac{L}{2}$ from that point longitudinal force of 5x ...
1
vote
3answers
153 views

How are the half life of particles mathematically related to the inverse square laws?

This video https://www.youtube.com/watch?v=K6i-qE8AigE&list=PL3B0924C6A0CB8B67 explains how forces are boson particles. It talks about the other non-force particles giving off and creating bosons, ...
0
votes
2answers
314 views

Why liquids in hydrostatic equilibrium stay at the same height? (open tubes)

This part of the book says that, because the two liquids have the same pressure at the same height (that's true), then if a liquid has a higher height, the liquid would have more pressure at a ...
1
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0answers
45 views

Will the usage of Exo-Skeleton Gear actually weaken the human body over time? [closed]

As we all know, Exo Skeletons as they exist now are just a series of Force multiplying apparatuses working together, also the human body changes to accommodate environment specific factors in order to ...
2
votes
3answers
96 views

Why do Signs Fall?

My question in this post is, why do signs with large angles fall? For example, fold a piece of paper in half, set the angle between the two halves, and place it on the floor; it will stand or collapse ...
1
vote
1answer
273 views

How does one figure out how fast water is moving through a water intake on a dam?

Say the dam is Hoover dam for example. The intake is where the water flows in to turn the turbines that generate electricity. I want to know if there is an equation that describes the speed of the ...
0
votes
2answers
144 views

A model that unifies the strong, EM, weak and gravity forces?

Does there exist such a model that explains the force clusters (their origin, relations between them): the strong, EM, weak and gravity forces?
2
votes
2answers
854 views

Why does iron sink in molten iron instead of floating?

Why does iron sink in molten iron whereas ice floats on water? Both are solid states of their own form, so why is one floating and the other sinking?
0
votes
2answers
71 views

Work in electric potential

I've read that if we want to move a charge in an electric field then we need a work of an external force to move it from a low potential energy to a high one , but then I read on another source that ...
0
votes
2answers
135 views

Is the Fundamental Theorem of Calculus really applicable to the definition of work?

When the force $F$ on an object is not constant, then the work it performs is defined as $$W = \int_{x_0}^{x} F(X)dX.$$ Now, the Fundamental Theorem of Calculus states that $$\text{If}\,\,\, f(x) ...
2
votes
4answers
968 views

Newton's third law.. please explain here

According to Newton's third law, the force acting on object is equal and opposite to the other object that is applying the force. If I push a table with 5N force then table is doing the same. But the ...
1
vote
2answers
531 views

Is jumping the result of normal force or action-reaction?

Just a clarification question based on an example I read about. Can normal force do work on an object? The answer is yes, with an example being a person jumping. The normal force causes work to ...
5
votes
3answers
1k views

Has a body angular momentum and torque only in a circular path?

In different contexts, my book(Principles of Physics by Resnick, Halliday ,Walker) , they wrote For torque, the path need no longer be a circle and we must write the torque as a vector $\vec{\tau}...
4
votes
5answers
6k views

Force required to drive car

From what I know of Newtonian Mechanics, if an object is moving at a constant velocity, the net force acting on that object is equal to zero. If there is friction, then the applied force required to ...
0
votes
1answer
104 views

Determine reactance force of four load cells arranged in two dimensions

I have constructed a "force plate" to reconstruct the location (x,y) of a steady state contact point force f. The system consists of four fixed compression load cells L1, L2, L3, and L4 and a thick ...
0
votes
2answers
98 views

Mathematical misunderstanding of Work-Potential Energy Theorem?

This is a relatively basic question, but I don't understand why it is the case. This is from my dynamics book and is mainly a mathematical misunderstanding. $$ \ dU = F\cos\theta ds $$ Which means ...
1
vote
1answer
130 views

Metallic coin over wooden block in glass of water

So there is some water inside a container; the height of water inside the container is $l$. I placed a wooden block on the water and it's floating to some height $x$, on top of the block is a metallic ...
4
votes
1answer
503 views

What is the effect of water 'climbing' over a cup via a wet string? [duplicate]

I have noticed (with tea bags, etc) that if you get the whole string wet, and you have one end inside the cup and the other end below the level of the liquid (outside), the water drains down the ...
1
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0answers
138 views

Suspended mass in motion free-body diagram [closed]

A 20kg mass is held by two ropes which span 90 from each other. The mass is being accelerated at 1m/s^2 to the right. Draw a free body diagram for the mass and find the numerical values for each force ...
1
vote
1answer
214 views

How much pressure do wheels exert on the ground?

I would like to know how much pressure 4 "rigid" wheels (as opposed to tyres) would exert on the ground; I've been on the case for hours now and the best I've come across to calculate this was the ...