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
3k views

Why is the mechanical advantage of a wedge = length of slope/ width?

Mechanical advantage is defined as Force Output/Force Input For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, the articles ...
1
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1answer
189 views

Can two bodies of different mass attached at ends of string passed over a frictionless pulley produce equal tension on both sides?

In my textbook there is given a case that to calculate acceleration and tension produced in string when string is attached at it's ends with two bodies of masses such that $m1>m2$ and the tension ...
0
votes
1answer
204 views

Why are hockey pucks so indestructible?

After watching a hockey puck be exposed to extreme heat as well as extreme cold, the puck seems to end up in pretty good shape. I can sort of understand the puck vs. hot ball of nickel since the area ...
0
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1answer
23 views

Motion of an electric charge within an electric field with two electric charges

Assume that air resistance and gravity are negligible and the only significant force acting in the scenario is the electric force. There are two electric charges, both with an equal and positive ...
1
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1answer
44 views

Black hole gravity vs parent star gravity

In the cases of black holes that form from supernova and collapse of a massive star, I understand that in most of these cases, the star loses significant amounts of mass from the explosion. ...
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0answers
24 views
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2answers
38 views

Force on a Massless String

Suppose we are just pulling a block with the help of a string which is massless. Now since the mass of the string is 0 the force exerted by us is transmitted without being diminished. So the equation ...
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2answers
61 views

Doubt on series springs

Here is a description of the motion of two springs in series. The premise is that the force on the two springs is the same. This is derived from the following reasoning: when I pull the mass with a ...
0
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1answer
125 views

Can two bodies move with equal acceleration if forces acting on both are unequal?

In my textbook there is a case given that is to find acceleration and tension produced in a string passed over a frictionless pulley and attached with bodies of different masses at its ends. Now below ...
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0answers
28 views

What is the maximum speed without skidding on a circular path? [closed]

What is the condition that the body going on the circular path will skid if its speed is increasing at a constant rate, say a? I need a free body diagram too.
2
votes
1answer
145 views

Newton's Third Law As Discussed in Den Hartog's Mechanics

A question, but some preliminaries in order to avoid answers involving concepts not yet introduced in the text I'm reading--Den Hartog's Mechanics. Near the very beginning of his book, Den Hartog ...
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0answers
20 views

Systems of Connected Particles [closed]

What are the all the forces acting on a wedge that is accelerating horizontally carrying a particle that is also accelerating down its slope?
5
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3answers
78 views

The motion-independent definition of force

I think we must be able to accomodate a definition of a force on some particle which is independent of the motion of the particle, for all kinds of forces, to surely verify the statement like 'force ...
2
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3answers
2k views

When is tension constant in a rope?

Suppose we have a massless rope with pulling forces applied at each end. In which scenarios is the tension in the rope constant throughout? For example if there is a knot in the rope the tension is ...
0
votes
1answer
52 views

Solenoidal forces

As far as I know a solenoidal vector field is such one that $$\vec\nabla\cdot \vec F=0.$$ However I saw a book on mechanics defining a solenoidal force as one for which the infinitesimal work ...
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2answers
49 views

How can one calculate the force and time of impact?

How does one calculate the force and time of impact of a body colliding into a stationery body please? Can one use Newton's 2nd law of motion?
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2answers
60 views

Tension and friction. Cool question

I had an exercise like the image, where block A is pulled by a force F, there is that rope(tension) attached to the block B and the wall, and there is friction between A and B, and A and the ground, ...
0
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0answers
54 views

Is it wrong to equate the net force to the force by the spring to find its maximum expansion?

In the picture displayed here , I have two blocks of masses m1 and m2. They are connected by a spring and a leftward force is applied on the block of mass m1.This will , ofcourse , result in ...
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0answers
14 views

Inertial force of fluids [duplicate]

Reynold's number is the ratio of inertial force to viscous force.I also know the definition of inertial force.but where does a fluid get this force from?what are the factors responsible for this ...
0
votes
1answer
231 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 ...
4
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0answers
329 views

What are the accelerations of blocks? [closed]

I've talked with 2 teachers about this situation: one teacher said he was completely sure that B have twice the acceleration of A, the other said he was completely sure they have same acceleration. ...
3
votes
1answer
91 views

High Level Understanding Q: What *is* a magnetic/electric field?

Note: I have seen this question -> (What is a magnetic field) and would still like some clarification. I have also seen https://www.youtube.com/watch?v=hFAOXdXZ5TM and ...
0
votes
1answer
9k views

Average Resistive force exerted by a wooden block on a bullet [closed]

A bullet of mass 0.04 kg moving with a speed of 90 m/s enters a wooden block and is stopped after a distance of 60cm. What is the average resistive force exerted by the block on the bullet? Ok, so ...
0
votes
1answer
38 views

Difference between sudden force and impulsive force? [duplicate]

What is the difference between a sudden force which continues to act on the body, and an impulsive force? What would be respective speeds of the body just after time= 0?
1
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2answers
51 views

Centripetal effect or curved space time

I think I understand both the centrepedal effect and Einsteins curved space time. However I am confused about which best describes the motion of a planet ( or other orbiting body ). Simply put, does ...
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6answers
53 views

Resultant forces

In my text book they said that: If no resultant force acts on an object, it will not accelerate; it will remain at rest or it will continue to move at constant speed If an object is at rest ...
9
votes
1answer
459 views

What are the proposed theoretical explanations for the EmDrive?

The EmDrive is a proposed propulsion mechanism for spacecraft in which some form of microwave device provides the propulsion. The consensus from the physics community, including many voices on this ...
0
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4answers
251 views

Forces Create Angular Acceleration And “Straight” Acceleration - But How Much Of Each?

Let me set up the following problem for a rectangle floating in space: We know its dimensions. We know its mass. There's a force pushing it for a known amount of time - we know the angle & ...
0
votes
1answer
106 views

Magnetic interaction of wire and rectangular loop

In this video, Prof. Lewin shows an infinitely long wire and a rectangular loop at a distance $r_1$ from each other, each carrying a current. He then calculates the magnetic field resulting from the ...
53
votes
4answers
3k views

GR and my journey to the centre of the Earth

[General Relativity] basically says that the reason you are sticking to the floor right now is that the shortest distance between today and tomorrow is through the center of the Earth. ...
0
votes
1answer
55 views

Is force exerted by Earth different for different mass?

We know Earth pulls every object by the same acceleration $g$ (say). force exerted by earth $F=m\cdot g$ (with $m$ the mass of the body), so, if $g$ is constant then $F$ is directly proportional to ...
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votes
1answer
33 views

Question about Thrust; am I correct?

Basically, here's what I understand about Thrust: Thrust is a force. You get it by doing $v\times\frac{dM}{dT}$. Pretty basic, because that's the formula you're given. However, because I'm trying to ...
0
votes
2answers
33 views

What would happen to a motor without a split-ring commutator?

I realise that a similar question has already been asked (Why does the coil in this apparatus reverse its direction of oscillation?), however after reading the answers, I am still unclear on certain ...
1
vote
1answer
20 views

Normal force and weight

If two books are placed on top of each other on a table, why would it be incorrect to say that the weight on the upper book acts on the lower book? I thought that the weight of the upper book would ...
2
votes
2answers
1k views

Average Force vs Net Force

The F in $$Impulse = F*t$$ is said to be the average force. For a ball dropped vertically onto a horizontal surface, the average force, F, on the ball from the floor is: $$F = \frac{\Delta{p}}{t}$$ ...
0
votes
2answers
27 views

Trouble understanding non-conservative force and work

I am having some trouble defining whether a force is conservative or not. In the example that we are working on a mass on a pulley system is used to cause a slender bar to rotate from rest to a ...
3
votes
6answers
148 views

When we write that $F = -\nabla V$ , what would happen if we ommit the (-) minus sign

I have had this question for a long time. In classical mechanics, if we choose $\mathbf F = -\mathbf \nabla \, V,$ with the minus sign, we can proof the work - kinetic energy theorem. What are the ...
1
vote
2answers
154 views

If I double the amount of oxygen molecules, do I double the paramagnetic force?

Oxygen is well known to be paramagnetic. If I take one molecule, $O_2$, and measure its paramagnetic force due to externally applied magnetic field, and then add another molecule near the first ...
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0answers
10 views

How to calculate pull force of a solenoid with permanent magnet plunger (NdFeB)?

The solenoid is air core. If we use permanent magnet like NdFeB as a plunger, how to calculate the pull/push force of the solenoid with plunger?
4
votes
1answer
411 views

Derivation of force law in special relativity

I've seen force defined in special relativity as the rate of change of 4-momentum $$ {\bf{F}} = \frac{d {\bf{p}}}{dt} $$ Can anyone comment on the following derivation of that relation? Take one ...
1
vote
2answers
31 views

How can you tell if the work done by a force is negative?

This is kind of confusing to me. I'm guessing that it's specific to the problem. Is the work done by friction always negative? Is the work done by gravity always negative? Spring as well? It seems ...
0
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0answers
28 views

What amount of force could be created by a person “swimming” in air?

Had a question on a physics test, a person is at rest on a frictionless surface and can not throw anything, can they move? I said yes, by "swimming" against the air and got docked because "it ...
1
vote
1answer
30 views

Tensile strength of a chain of electromagnets

I was having a discussion about the tensile strengths of various materials. Could something like a chain of electromagnets be made to have a tensile strength proportional to the power applied to it? ...
0
votes
1answer
208 views

We cannot solve this inclined plane problem, right?

We drag a sledge along a snow-covered hillside with constant speed. Distance is 150m. The time it takes to reach the top is 300 secs. The sledge is 12kg. And the coefficient of friction $\mu$ = 0.04. ...
1
vote
3answers
180 views

The speed of air rising through a heated tube

I would like to get an explanations of an observed physical phenomena. When a metal tube is placed vertically and heated and the air inside rises, the speed of the air moving through the tube ...
1
vote
2answers
56 views

How is a mass, suspended vertically by two springs in parallel, kept stable? [closed]

Consider a mass suspended vertically from above by two springs in parallel with different spring constants. Wouldn't the tension be different in each spring? How is this system kept in equilibrium?
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0answers
48 views

Determining the forces required to maintain a static center of mass position; one with velocity and one with acceleration [closed]

I'm having a bit of trouble wrapping my head around this conceptually. The magnitudes and directions of the forces on two of the particles are indicated. What are the magnitude and direction of the ...
1
vote
2answers
349 views

Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newton's third law and momentum conservation. Here is what I have tried. Lets take a ball mass of $m_1$ (index 1 is the ...
2
votes
1answer
137 views

induction of van der Waals forces

Is there a way to maximize van der Waals forces between two materials, by electrifying one material, thus creating dipoles/instantaneous dipoles and thus creating stronger van der Waals forces? has ...
0
votes
1answer
45 views

Force of baseball bat given force of ball and recoil distance

Say I swing a baseball bat and hit a ball. The ball is moving at 60 miles per hour and impacts the baseball bat squarely at that speed. The ball has moved twenty feet before impacting the bat. The ...