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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Direction of acceleration at highest point

When a ball is thrown vertically upwards, what will be the direction of acceleration at the highest point(where velocity is zero)? Upwards, downwards or arbitrary?
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1answer
13 views

Interaction pairs- how they can cause movement

Back to basics with this question but I really want to make sure I understand this concept. Newton's third law states that 'every action has an opposite and equal reaction', which we can see through ...
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1answer
22 views

When an object hangs from a Rigid rod is the force of the weight located in the center of the sign?

From the rope that supports the sign (assuming the mass is distributed evenly). If the length of the sign is, $L$ can I model it so that the weight is concentrated at $\frac{L}{2}$ Therefore, the ...
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4answers
842 views

Is force a contravariant vector or a covariant vector (or either)?

I don't understand whether something physical, like velocity for example, has a single correct classification as either a contravariant vector or a covariant vector. I have seen texts indicate that ...
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0answers
35 views

Thermodynamic derivation of condition for equilibrium of triple line

Edit:(4/1/2016) Okay, I get how the required equation arises from force balance. All forces are acting on the same length, so the length cancels out of the equation and what we've got is essentially ...
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0answers
39 views

Finding the acceleration of a block using Newton's Laws [closed]

I am stuck with a Newton's Law revision question. I can do them okay when all the objects and forces are in a straight line, but this involves a pulley system, where one object is at 90 degrees to ...
2
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1answer
46 views

Changing the length of a spring [closed]

Imagine we have a spring that is hanging from the roof with $k = 200$ and a stone with $ W=10N $ is pulling it down. Then due to $$ F=kx $$ we have $x=.05m=5cm$ Now we halve the length of the spring. ...
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0answers
14 views

The amount of force needed to bend and break a magnesium cylinder? [closed]

I want to determine how much force in Newtons will be need to bend a solid cylinder of magnesium. The cylinder is (x) cm in diameter, and it is (l) cm long. The density of normal magnesium alloy is ...
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5answers
1k views

What force causes the ball to move up?

Let's consider this super-simple example. The ball (mass $m$) is moving from position 1 to position 2 at constant horizontal velocity $v$ until the ball reaches the red arrow (in position 1, it has ...
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0answers
25 views

How forces divide in pulley series? [closed]

I'm trying to solve a question , It's about a lat pull fitness equipment. Here you can see what's the equipment : When someone start pulling down, How do forces divide between two pulleys ? I mean ...
2
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2answers
80 views

how does one divide stress in such a bridge? [closed]

I want to build a spaghetti bridge like this: I have two spaghetti types: T-type (designed to tolerate tension) and C-type (designed to tolerate compression). A mass $m$ is hanging from the point ...
1
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2answers
53 views

How is the equation for force by charge or by mass discovered?

It's a newbie question. How is the formula for force between two charges or gravitational force between two particles derived. Is it just intuition or is there any method used to derive these ...
2
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0answers
31 views

Applied forces on a bridge [closed]

What are the forces that acted on the 6 types of bridges? Beam, Truss, Cantilever, Arch, Suspension, and Cable-Stay? What formulas do you use to get the forces? I'm curious since there is ...
1
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0answers
29 views

Unfamiliar force of friction in materials [closed]

I have never faced with questions that friction effects more than two time until last week that one of my friends gave me this question : We have two surfaces : Sur1: with coefficient of static ...
3
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2answers
68 views

Understanding Density and the Buoyant Force

A beaker of water resting on a scale registers a weight of 0.61 N. Lowering a steel cube completely into the water (without making any contact with the beaker) causes the reading on the scale to ...
1
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0answers
25 views

How can a net force of 0 still lead to movement and how is movement possible with interaction pairs? [duplicate]

So I always thought of movement as interaction pairs. For example, I thought that a rocket moves by applying a force of hot exhaust gases, which then apply a reaction force back on the rocket ...
5
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3answers
595 views

Is there any tension in a massless spring that connects two free falling bodies in different horizontal planes?

Two bodies A and B of same mass $m$ are attached with a massless spring and are hanging from a ceiling with a massless rope. They are in same vertical plane but not in same horizontal plane. Now the ...
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3answers
66 views

Violation of Newton's third law

consider the following situation shown in the diagram below.A huge wall of mass M is moving to the left due to a constant force of 100N. Now suppose a man of mass m applies a force of 20N to the ...
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1answer
66 views

Max Acceleration on an incline? (2010 F=ma #8) [closed]

(From 2010 F=ma, #8) A car attempts to accelerate up a hill at an angle θ to the horizontal. The coefficient of static friction between the tires and the hill is µ > tan θ. What is the maximum ...
3
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0answers
56 views

How is Temperature and Pressure related to when a tire rolls on the ground?

Actual observation: Here in Canada it is known that even when 'dry' snow is on the ground, and when a car drives over it that small amount of dry snow instantly becomes ice (NOT GOOD). Anyways as an ...
1
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1answer
39 views

Force (torque) to break a bike handlebar? [closed]

Few weeks ago a neighbor manage to hit my bike with his car while the bike was parked next to a wall, check the picture. One side of the handlebar was at the wall and the door of his truck hit ...
2
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1answer
44 views

Is the integral of $dK$ equal the work done?

$$\frac{dK}{dt} = \frac{d}{dt} (1/2 mv^2) = mv \frac{dv}{dt} = F\frac{dx}{dt}$$ $$\implies dK = F. dr$$ Also, work is defined as $W = \int F. dr$. So does this imply integral $dK = W$?
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2answers
42 views

Does it take a larger force to stop a faster object?

Does it take a larger force to stop a car that is moving at a velocity 2*v than if it is moving at a velocity v? I'm confused as the force required to decelerate a car depends on the mass and the ...
2
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1answer
53 views

Pascal's law and pressure gradient

Pascal's law states that pressure applied on an ideal liquid is equally distributed. Then why is there a pressure gradient in a liquid body? Please let me know what is wrong in what I stated. What ...
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1answer
30 views

can a single force rotate an object. not a torque

Can a single force (not a torque) rotate an object? How can the bar below fall given the force $\mathbf F$?
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1answer
27 views

How far will the key slide? [closed]

A person tosses his car keys on a shelf with an initial velocity of $2\:\mathrm{m/s}$. How far will the keys slide if the coefficient of kinetic friction between the surfaces is $0.3$? How would you ...
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3answers
57 views

When walking, why the foot which get the reaction doesn't accelerate?

To walk we apply a force and the earth gives us a reaction. But the foot which get the force doesn't accelerate.
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3answers
74 views

Why can't we define a potential energy for a non-conservative force? [closed]

We could define potential energies for non-conservative forces too and then we could conserve it with kinetic and potential energy as we know it. But no one does that. Why is this? Please explain. Any ...
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2answers
77 views

Does a man run a same distance with different velocities spend the similar energy?

To simplify the question we assume the same man run on a straight and flat road with constant speed. Personally I don't believe the man would spend a similar energy. But how to prove it in physics? I ...
2
votes
3answers
34 views

What is the gravitational pull if one has as much mass above them as below them? [duplicate]

I understand the previous responses to other answering if you were at the center of a planet, would you be weightless? Yes you would due to the forces of gravity pulling at you from all sides. ...
0
votes
1answer
107 views

Can Newton's 3rd Law be considered as a direct consequence of the coulomb's law of electric interactions? [closed]

Let me explain my thought. Lets consider Coulomb's definition of electric force between two charges as the fundamental law. Under this consideration, forces between charges already follow What ...
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2answers
24 views

Confusion regarding resolution of forces

I'm looking at a basic free body diagram of a car travelling on a banked(inclined) road with inclination theta. It's mass is 'm'. Here the diagram shows weight (mg), Normal reaction(N), and ...
0
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1answer
74 views

What is the speed of magnetism?

I'm not a physicist (just have a few basic notions) and this is a question out of curiosity, so as I'll probably word it the simplest I can, please take that into account when answering. tl;dr Let's ...
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2answers
41 views

Horizontal net force question [closed]

A 1580kg car travels at 15m/s, what would the magnitude of the horizontal net force required to bring the car to a halt in 50m?
5
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4answers
39k views

What is the relationship between Force and Kinetic Energy?

I am an Middle-School (Grade 8) student, who is self-learning classical mechanics. I saw this equation from Classical Mechanics: $\vec F=m \vec a$, the following equation is pretty straight forward ...
12
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2answers
4k views

If atoms never “physically” touch each others, then how does matter-antimatter annihilation happen?

It is known that matter and antimatter annihilate each other when they "touch" each other. And as far as I know, the concept of "touching" as our brain gets it is not true on the atomic level since ...
20
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1answer
772 views

What determines the speed of waves in water?

While I was walking my dog this morning, I passed over a canal filled with boats, barges, and kayaks all of different masses and moving at different speeds. I noticed that all of these vessels left ...
4
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3answers
394 views

What does it mean to say work is path-independent when pushing an object in different directions?

If I apply a straight upward(perpendicular to ground) force against gravity of $5\ \mathrm{N}$ and lift an object "A" 10 meters, then the work done is: $$ W = F \times S = 5\ \mathrm{N} \times 10\ ...
1
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2answers
40 views

Equilibrium on a fixed wedge

While solving a question I came acrross this doubt.For a block in equilibrium on an inclined wedge, the summation of forces should be equal to zero.I am confused because I got two different results ...
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0answers
18 views

Point charge inside a electrically neutral cavity in conductor placed eccentrically, and effect of external electric field if switched on

bear with me, but i would like a definite answer, now, starting off the external charge density on the outer surface of sphere WILL be uniform by unique solution of Laplace equation and letting the ...
0
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1answer
43 views

Why there is an extra componet of force in this Equilibrium state?

I have a question about the forces on a body at equilibrium. Look to this image: here i draw a man standing with a pen on earth. And I think that I draw all possible forces on it. They are as ...
1
vote
1answer
88 views

Are pull ups as performed by Oliver Queen in the TV series The Arrow possible?

Referring to the pull ups performed by Oliver Queen in the TV series The Arrow. My hunch is that such pull ups are impossible because it violates the law of physics: as Oliver tries to pull himself ...
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1answer
130 views

Is this picture of relativity correct? [closed]

Can forces be said to exist in a real sense in general relativity?
0
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2answers
39 views

In a vacuum, given two identical objects, if one is stationary, what would happen if the two objects collide?

Given these two identical objects, if one is stationary, and the centre of mass of the other object collides head on with the centre of mass of the object that is stationary, i.e it does not come into ...
0
votes
1answer
47 views

How are unbalanced forces even possible, given Newton's 3rd law? [duplicate]

The notion of an unbalanced force seems to contradict Newton's third law, entirely. For instance, apparently, if you push a rock, then an unequal force is being applied in the opposite direction with ...
0
votes
3answers
293 views

Is there a normal downward force here?

Now through my understanding, there is a weight force that points downward on block A, also another weight force that points downward on block B. Between block A and block B, there is two normal ...
0
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0answers
11 views

Stick stands in the corner then starts to fall, when will it detach from the wall? [duplicate]

A thin homogeneous stick stands on the smooth(no friction) floor, leaning against a smooth wall,stands absolutely vertically. (Imagine a corner).Then it starts to fall(with zero initial velocity).What ...
7
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6answers
3k views

Gravitation is not force?

Einstein said that gravity can be looked at as curvature in space- time and not as a force that is acting between bodies. (Actually what Einstein said was that gravity was curvature in space-time and ...
1
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0answers
49 views

Pulley system on a double inclined plane [closed]

(Lets say, say static friction is $\mu_s$, and kinetic friction is $\mu_k$ for both of them) What is the detailed definition of static friction according to this picture? When the system starts to ...