Questions tagged [forces]

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 the [particle-physics] tag for decay channels due to forces and [newtonian-mechanics] or one of the other subtopics of [classical-mechanics] for the dynamics of classical systems.

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Its a physics exam question, I and my friend don't understand the theory and mechanics behind it [closed]

Two spheres each of mass m are connected by string of length 2l, are kept on a smooth horizontal surface. A vertical force F is applied at the middle of the string. What is the max value of F for ...
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1 answer
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What is the work done by friction on a body from the perspective of different observers using the formula $-μmgl$?

Consider two observers moving with respect to each other at a speed $v$ along a straight line. They observe a block of mass $m$ moving a distance $l$ on a rough surface. The change in KE of the block ...
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1 answer
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Concept of work [closed]

How was the concept of work and energy invented in physics? What is the actual idea behind work and energy? Why are distance and force specifically used to define work, why not time instead of ...
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The work done by tension and normal forces are conservative or non-conservative? Give reasons [duplicate]

The work done by tension and normal forces are conservative or non-conservative? Tension as well as normal forces does work but has no field. Simultaneously their work is not always path dependent. ...
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4 votes
7 answers
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Trying to understand Newton's Second Law [closed]

If I apply a force on an object at rest and it’s velocity is constant (after force is applied) wouldn’t that mean that the acceleration is 0? Then how would $F=Ma$ make sense? My thinking here is that ...
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Pulsed Fluid jets

While feeling my shower head, switched to "pulsed jet" mode, exert a higher force on my body as compared to a regular flow jet, I have wondered why a pulsed jet is stronger than a non-pulsed ...
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Linear pull vs pulling at an angle [duplicate]

Why it seems much easier to pull an object in the horizontal plane, by attaching the rope to a "non moveable" object and the object that we need to move, then lifting the rope in the middle. ...
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1 answer
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Pressure in stokes flow

In the stokes equation for an incompressible fluid, there is a pressure term that enforces the fluid to have $\nabla \cdot u=0$, where $u$ is the velocity field. The stokes equation reads: $$\eta \...
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How to create a friction-based cable exercise machine? [closed]

What would be the best mechanism to create a friction based cable machine? The point of this machine to only have resistance to movement not when the cable's stationary and without the momentum of ...
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1 vote
2 answers
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How much time after will two oppositely charged particles collide for both gravitational force and electrostatic force?

Suppose two point objects charged with opposite charges $q_1$ and $q_2$ at a distance $r$ in a vaccum. So, the net electrostatic force on both objects $= F_c = \frac {q_1q_2}{4π\epsilon_0r²}$ [$\...
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General treatment of surface tension non-relativistic classical theory

I'm reading lecture notes on fluid mechanics course, and I wrote that an algebraic definition of surface tension can be constructed from work per unit area to balance the forces along the surface. ...
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3 answers
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Which tube experiences a larger buoyant force?

I saw lots of debate about this question. Some are saying that this cannot be solved because the weight of the tubes is not given. Others say the red one experiences more buoyant force because for red:...
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1 answer
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How non-collinear forces balance each other?

In the system of parallel forces , all the forces are non-colinear. So how to they balance each other?. Here in this case a wooden plank is supported at its end by two supports. All the forces here ...
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4 answers
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Does this prove that the force and momentum formulas are wrong? [closed]

Imagine someone is pressing a cube with his thumb and index finger, and there is no motion in the system. Is the cube really under pressure? If the cube is under pressure, how we can justify that ...
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Would water flow in the following system? [closed]

Would water flow in the following system?
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Problem solving - Newton's Inverse Square Law of Gravitation [closed]

(a) How far from the center of Earth would the net gravitational force of Earth and the Moon on an object be zero? (b) Setting the magnitudes of the forces equal should result in two answers from the ...
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Why does Newton's second law involve mass?

Once one has learned of Electromagnetic force, they see that the amount of force experienced by particle given a field is proportional to the particles electric charge. Similar situation the ...
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1 answer
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How to obtain nodal forces from stress tensor?

I am working on a FEM code in which I need to obtain the force vector on each node of a triangular linear element from the stress tensor in 2D. I have the shape functions, and the stress is constant ...
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A proton and an electron are placed in a uniform electric field successively. Do these two particles experience the same force? [closed]

A proton is placed in a uniform electric field and then released. Then an electron is placed at this same point and released. Do these two particles experience the same force? The same acceleration? ...
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4 answers
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Why is angular momentum equal to mass times radius times velocity?

When momentum is mass times velocity, why is angular momentum mass times radius times velocity?
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Would it be correct to state that the damping force and the spring force are equal in the case of critical damping?

(Note: this question is for a spring mass system moving through air) Intuitively it makes sense to me that they would be equal to each other, but I have not found a clear answer referencing the forces....
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1 vote
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Liquid Oxygen and its paramagnetic properties

How do you calculate the magnetic attraction force on liquid oxygen due to a strong permanent magnet? And if calculating it by hand isn't an ideal solution, which software is the best for handling ...
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Why do we use moment of inertia about centre of mass to calculate rotational KE in rolling without slipping?

Say we have a cylinder rolling without slipping on a horizontal plane: Now, the instantaneous centre of rotation is P, so we can use $ v_A=\omega \ r_{AP}$ to find the linear velocity of the centre ...
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Newton's third law cancelling

I have recently been doing some work around Newtons third law. And I was thinking about a question revolving around the topic. It is a common question of how can we move at all if all forces are equal ...
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2 answers
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Why forces exerted by fluids, inside or outside, are always perpendicular?

I was learning about pressure due to fluids when I encountered the lines such as 'liquid layers exert perpendicular force on each other, fluid exert force on a body perpendicular to it in all ...
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Calculate the force acting on a dipole at an electric field [closed]

I have the following question: There are two electric charges at $(-a,0,0)$ and $(a,0,0)$ with the charge $Q$. A dipole with dipole moment $\vec{P}_{el}$ is placed at $(0,0,0)$ and is oriented in the ...
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1 answer
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How much does the sky weigh? [closed]

How much does the sky weigh? I don't know how much the sky weighs. Is the sky gravity? I tried researching, but I can't find scientific information that is proven.
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Calculating the moment/torque of a force applied over an area [closed]

This diagram shows a current carrying wire (from PQ) and a uniform magnetic field applied across the wire (from 85-90 cm) into the page, therefore the force is upward. How would one calculate the ...
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Conservation and potential with non-cartesian forces

I understand how to determine if a force is conservative from \begin{equation} \nabla\times \mathbf{F}=0 \implies \mathbf{F}\text{ is conservative} \end{equation} When $F$ is in cartesian coordinates. ...
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1 vote
1 answer
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Minkowski's equation of motion

I'm trying to prove $f^{\mu}U_{\mu}=0$ for four-force $f^{\mu}=c\frac{dP^{\mu}}{ds}$ and four-velocity $U_{\mu}$. I start by using the chain rule, $f^{\mu}=c\frac{dP^{\mu}}{dt}\frac{dt}{ds}=\gamma\...
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2 answers
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Problem with possibly infinite possible solutions [closed]

Problem figure: In the problem, the string is light, inextensible and initially, before the application of the external forces, the string is just taut with no tension and the blocks were at rest. ...
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Boussinesq Approximation Term in Momentum Equation

According to the Boussinesq equation: $\rho = \rho_o ( 1 - \beta_t ( t – t_o) - \beta_c ( c – c_o ) ) $ So, $\rho \cdot g$ should be equal to : $\rho g = g \rho_o ( 1 - \beta_t ( t – t_o) - \...
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The direction of force on a current carrying coil rotating in a magnetic field

If we have a current carrying coil that is rotating between two magnets where the south and north poles face each other, does the force on the coil change direction as the coil rotates. The force on a ...
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0 votes
1 answer
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A ball of mass 22g moves to the left at a speed of 35 m / s [closed]

A ball of mass 22g moves to the left at a speed of 35 m / s. How much work needs to be done on the ball to start moving to the right at a speed of 35 m / s. When considering ignore any energy losses
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Is the system of parallel springs always have a same extensions?

In a normal system of parallel springs, We say that their extension of the each spring is same, so the equivalent spring constant k is the sum of all k of spring. But how can this make sense if one ...
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1 answer
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How to find the magnitude of the maximum transverse acceleration of a given point on a string? [closed]

A thin string 2.50 m in length is stretched with a tension of 90.0 N between two supports. When the string vibrates in its first overtone, a point at an antinode of the standing wave on the string has ...
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Ball attached to string snaps in decelerating car

A ball hanging from the ceiling in a decelerating car will make an angle. What happens if the string snaps while the car is decelerating? As gravity is the only force acting on the ball after the ...
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2 answers
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Is the Planck force a truly "Planck unit"?

The Planck force appears to be defined as the ratio of the Planck energy to the Planck distance, $ F_P = E_P/l_P $ that can be rewritten as $$ F_P = \frac{ E_P }{ l_P} = \frac{ c^4 }{ G }. $$ Isn't it ...
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Fundamental-ness of fundamental forces

Example : Consider a black hole and it's event horizon of radius R surrounding it . Suppose in the direction of a diameter of the black hole ( or event horizon) , there are two charged particles. ...
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Calculate the change in velocity from a spinning ball at impact

When a ball hits a surface, if there is no spin, it bounces with a simple reflection of the velocity prior to the impact. But when the ball has spin, the friction between the spinning ball and the ...
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-1 votes
1 answer
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Energy and force relation

So in simple machine we apple less force with more displacement to exert same energy as the load need so if energy is related to tiredness i.e. more energy you lose more tired you feel but by applying ...
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1 answer
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Splitting gravity along $x$, $y$, and $z$ axes

For my diploma project, I am building a posture correcting wearable, being able also to recognize some activities such as walking/running, climbing stairs, etc., and for this, I am using some ...
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2 answers
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Does the change in velocity of a body due to a space-depending force depend on the initial velocity of the body?

Let's say, for simplicity, that we have a line, and over a segment $AB$ of this line is being exerted a constant force $F$. A body $P$ travels from $A$ to $B$. My question is: does the change in ...
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3 answers
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What forces act on an element taken in a body which is subjected to no external forces?

Consider a block (rigid) which is lying on a table. If we take a differential element in the block and try to draw its Free-body diagram, will there be any forces other than gravitational force acting ...
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4 votes
4 answers
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With how many Newtons of force is the universe expanding?

The universe is expanding at an accelerating rate. They key word here is "accelerating". Meaning that there is an equivalent "force" (in Newtons) that would cause that same ...
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What's the amplitude of the energy loosing oscillator as a function of time?

The problem comes from 'introduction to classical mechanics' by David Morin. It is as follows: A chain with mass density $\sigma$ kg/m hangs from a spring with spring constant $k$. In the equilibrium ...
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1 vote
3 answers
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Are Newton's laws just definitions?

I have read a bunch of articles online regarding my question but none have helped. Newton's Laws: In an inertial reference frame, an object's momentum doesn't change unless the object is acted upon ...
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1 vote
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Force to Inflate a ball underwater [closed]

How much force is required to fully inflate (with air) a beach ball that is 6 feet in diameter at depths of 200 feet underwater?
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1 vote
2 answers
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What is the mathematical expression for the Higgs boson coupling constant?

I have been searching around and cannot get an expression for the Higg's coupling constant. By 'coupling constant', I mean for the strong force $$\alpha_S=\frac{{g_S}^2}{4 \pi \hbar c}\approx 0.1\tag{...
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Friction when a car is moving in a circle

When a car is moving in a circle, I want to know how the friction of the car could be drawn. I have found the following picture. But I know that the friction force is always in opposite direction of ...
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