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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Higher order derivatives - Equation of motion

One possible starting point to create a physical theory is the Lagrangian $L$. There we assume that the variation of the action $\delta S = \delta \int_{-\infty}^\infty dt \ L = 0$. In classical ...
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2answers
46 views

Force calculation with a fulcrum not working out [closed]

I hope this "applied" question can be asked here (and forgive my naivety in physics for the simple question). I've built the following murphy bunk bed: It rotates around the circles (the fulcrum) ...
0
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2answers
59 views

How to use an accelerometer to correctly quantify the magnitude of vibrations

Consider the following setup, an accelerometer is placed inside a helicopter, measuring "g" values along 3 axes (x,y,z) every 10 ms (100 times a second), during a helicopter flight. If one, wants to ...
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1answer
112 views

Tension when two connected blocks are pulled in opposite directions [duplicate]

Suppose there exist two blocks A and B connected by a massless, inextensible cord. Both A and B have equal masses and are acted upon by equal forces in opposite directions. So, is the tension in the ...
0
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1answer
40 views

Spacecraft momentum question [closed]

Assume you're sitting in your spacecraft. The mass of you and the spacecraft is 2000 kg. You're traveling at 200km/h through the vacuum of space. You have a thruster pointing in the direction you're ...
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0answers
106 views

Tension on a string pulled by unequal forces

Suppose two cases where masses are attached to massless, inextensible strings. In the first case a body which has a weight of 20 Newtons(downwards) is attached to a string which is acted upon ...
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1answer
57 views

How is gravitational lensing possible? [duplicate]

How is it possible that a force that affects mass (gravity) can affect massless particles like photons?
2
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1answer
216 views

Why do whips crack?

Whips have been discussed in a previous question last year. I wish to ask a further question on the subject. (I can not comment or reply to the previous question since I am a new member here and my ...
1
vote
1answer
51 views

Tension in an Atwoods machine conceptual?

Assuming $T_1$ is the force that acts on box $1$ and $T_2$ is the force that acts on box $2$. Exactly what causes the Tension? Why does $T_1 = T_2$? The problem is we are told to memorize that ...
2
votes
3answers
174 views

How do electrons actually move in a circuit?

Last year, we were taught about electricity, about how electrons in a closed circuit. But as our teacher had not taught us about electric fields yet, she gave us a simplified model of motion of ...
3
votes
2answers
106 views

What does an applied force on an already accelerating object do?

I'm a big beginner having only taken Grade 11 high-school physics. Imagine this situation: an object is accelerating north, and while it's accelerating, it's 'hit' by a northward force. To me it ...
0
votes
1answer
71 views

Will we feel the gravity of a star 10 light years away for the next 10 years if, somehow, it vanishes today from its position? [duplicate]

I was watching a relativity video, and although I am not sure, I felt that it was trying to tell that the effect of gravitation of a body is instantaneous, in the sense that a sudden change in the ...
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3answers
64 views

Proof that a force applied to the center of mass is the same as force applied off-center

There is a similar question that gives a bit of an explanation, but little mathematical proof here: force applied not on the center of mass I would like mathematical proof that shows that the ...
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votes
1answer
53 views

On conservative forces

We say if we calculate the work done by a force in going from 1 to 2 following a path say A is equal to -1 times the work done by the same force in getting from 2 to 1 following a path say B then work ...
1
vote
1answer
162 views

Block and Pulley Problem with Friction [closed]

1.) What is the acceleration of the hanging mass? (Indicate the direction with the sign of your answer.) 2.) Determine the tension in the cord. (Indicate the direction with the sign of your ...
0
votes
1answer
53 views

Curve of a rod bent by force on both sides

Suppose we have a flexible rod (i.e. it can be bent without breaking apart) and we excert a force on both sides, like this: If the force $F$ is not exactly horizontal, the rod will be bent and form ...
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2answers
338 views

What will happen if we put balloon in water tank in space

Imagine this. You have some object (let say barrel) and fill it with water. The water remains rather calm so it doesnt' spills out. Then we take a balloon filled with air and push it in that tank. ...
1
vote
4answers
261 views

Why is gas mileage typically better when traveling on the highway than on country roads or in the city?

The gas mileage of my vehicle tends to improve the more I have been driving on the interstate on that tank of gas - if I go through a tank of gas without at any point driving on the interstate, I will ...
2
votes
3answers
238 views

Is friction a product of Newton's third law?

Newton's third law is defined as $F_{12} = -F_{21}$ Is friction a product of this law? For example, if I take my hand and slide it across the floor in the $+x$ direction... My hand exerts a force ...
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1answer
68 views

Derive force from the pair-wise potential equation [closed]

How can we calculate the force exerted on particle $i$ by particle $j$ given a general potential function $V(d)$? Let's discuss this genenal question with a concrete example below. To simulate the ...
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3answers
259 views

Why is using Newton's First Law failing me?

A factory worker pushes a 29.7kg crate a distance of 5.0m along a level floor at constant velocity by pushing downward at an angle of 32$^\circ$ below the horizontal. The coefficient of kinetic ...
0
votes
2answers
79 views

force of hail falling straight

There is a hail storm and it's falling straight down (0 wind factor) will the hail meet a moving car with greater force than a car standing still?
5
votes
1answer
82 views

How can a reel of thread move in opposite direction?

There is a nice puzzle about reel of thread. I wonder why the solution works. The puzzle: You take a reel with threads on it. Inner radius r, outer radius R. You put it on a table. If you pull ...
0
votes
2answers
83 views

Is friction always constant?

Can the norm of the friction force change with time? Notice I said the norm which is in Newtons, can it change with time? Sorry if the question seems a bit confusing but I've done my best to explain. ...
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vote
2answers
84 views

How do we convert between the maximum value of the adhesive force (in kilograms or in Newton) of a magnet and its magnetic field strength (in tesla)?

On the following website they indicate how powerful is a magnet by giving the theoretical maximum value of its adhesive force in kilograms or in Newton (its adhesive force at a distance of zero). ...
1
vote
1answer
32 views

Clarification what exactly this question wants regarding force [closed]

I would like to ask you if the question asked What is the minimum force parallel to the plane, which can be prevent the block from slipping down the plane? I just did the calculation and and ...
0
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3answers
63 views

Solving for Normal Force

I'm working through The Nature of Code, which is an awesome book, lots of fun. I've come across Exercise 3.13 and I'm not sure how to solve it. I'm assuming that the force of gravity and the force of ...
2
votes
1answer
27 views

am i finding the force correctly?

I am trying to see if I am doing a problem correctly. Problem Suppose you carry a 50kg sack of potatoes up two flights of stairs, a total height of 10m. How much work did you do? If it took you ...
0
votes
1answer
42 views

How do internal forces affect motion?

As per newton's first law, only an external force can bring any change in the acceleration of a body, internal forces cannot. So, when we apply brakes to an accelerating car, aren't those ...
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votes
0answers
54 views

Why am I experiencing some type of odd motion?

So I noticed for a few years ago while I'm riding on the bus and as we stop at a corner i tend to just look at the road while I'm listening to music, I noticed that as the bus driver had stopped i ...
11
votes
14answers
3k views

Is Newton's third law always correct?

Newton's third law states that every force has an equal and opposite reaction. But this doesn't seem like the case in the following scenario: For example, a person punches a wall and the wall breaks. ...
2
votes
1answer
83 views

Relative strength of a dome

Is there a rough way to determine how the height of a dome affects the load that dome could support? For instance, assuming the bases of two domes are 24" in diameter, and one dome is 2" high while ...
3
votes
4answers
175 views

Definition of force, kinetic energy and momentum

I've edited the post. Q1 and Q4 are the important ones but I didn't delete Q2 and Q3 since some older answers would not make sense anymore. To begin with, the formula of the kinetic energy $T$ is ...
0
votes
1answer
52 views

Help me understand constant speed on a slope

An object is pulled up a slope at constant speed. I'm trying to find the Tension on the rope. $$m = 65kg \Rightarrow W=-637$$ $$\mbox{constant speed} \Rightarrow a = 0$$ $$\mbox{angle of slope} = ...
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3answers
41 views

In this particular problem: Is the mass of the system the mass of the person?

I am doing this problem: The upward normal force exerted by the floor is 620 N on an elevator passenger who weighs 650 N. What is the magnitude of the acceleration? This is how I solved ...
2
votes
1answer
55 views

Pulse Reflection

I wanted to ask why a pulse that reaches to a free end will reflect off and return with the same direction of displacement that it had before reflection. I am looking for explanation with forces.
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votes
1answer
87 views

Why $\vec F=m\vec a$ instead of $\vec F=m\vec v$? [duplicate]

$\vec F=m\vec a$ ,for moving object with 10 $km/s$ in a constant manner ,where acceleration is zero. ie No force on object ? http://www.physicsforums.com/showthread.php?t=622711
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votes
4answers
80 views

The work done by running in a rectangle

This may be quite off-topic but please help me. Is there any work done when I run in a rectangle? I thought that the answer should be no. But my teacher says that we should calculate each side ...
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votes
5answers
1k views

Force as change in momentum vs. change in velocity

Is there ever a situation where the distinction between $F = m \frac{dv}{dt}$ and $F = \frac{dp}{dt}$ is important? I can't think of a situation where one is true and not the other (assuming only ...
0
votes
2answers
102 views

Conservative Forces & Conservation of Energy?

I'm trying to relate them, I'm trying to find the key relation that would show how the conservative forces serve conservation of energy. How would they relate? Also, how are non-conservative forces ...
0
votes
2answers
161 views

Is the Lorentz force conservative? [duplicate]

Is the Lorentz Force acting on a wire, that has current $I$ in a magnetic field $B$ conservative? Or non-conservative? I understand that all the fundamental forces are conservative, am I correct?
3
votes
3answers
107 views

Time reversal symmetry in the presence of friction

I was reading a paper on time reversal symmetry, and came across an example of a pendulum swinging in the presence of friction: When we consider the more realistic physical situation of a swinging ...
0
votes
1answer
73 views

The force on an infinite line of charge perpendicular to a on a rod of charge

Essentially the question is to calculate the force exerted by a charged rod perpendicular to an infinite line of charge: $\vec{F}_{\text{rod}\rightarrow \text{line}} =\dots$ My question is it okay to ...
0
votes
1answer
636 views

Relationship between amplitude and frequency of a wave

I wanted to ask what is the relationship between amplitude and frequency of a wave. Some say there isn't , some say that there is , but from their answers the relationship is still unclear.
0
votes
1answer
533 views

Acceleration of masses hanging from a system of two pulleys

"Masses $M_1$ and $M_2$ are connected to a system of strings and pulleys as shown. The strings are massless and inextensible, and the pulleys are massless and frictionless. Find the acceleration of ...
0
votes
1answer
55 views

Question about pendulum

I came up with this problem by myself: How much force do I need to make a pendulum revolve? Now I imagined that the force $\vec{F}$ must be enough to make the pendulum swing until half of the ...
0
votes
1answer
73 views

Question on Newton's law

I have heard my friends referring to quantity ma as the "force of acceleration" whereas my teacher told us it can't be referred as so. Is it correct to refer that quantity a force? If not, how can we ...
1
vote
0answers
396 views

Sum of energy in a free rotation with Algodoo sofware

I try to understand why Algodoo software (freeware) give an efficiency greater than unity. I tested several scenes and at each time I can look the software give energy, I don't say it's all the time ...
0
votes
0answers
56 views

Creep of materials at atomic/molecular level under stresses

Do the viscoelastic materials creep at the same rate under three types of fundamental stresses, viz.- TENSION, COMPRESSION and SHEAR??? My intuition tells me that the answer is no. But, I can't get ...
1
vote
1answer
54 views

Help for orbits of planets

Suppose that an asteroid) that moves at a velocity $v$ passes near to a planet: now I know that the gravity force of the planet will curve the trajectory of the asteroid so I tried to make a draw of ...