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

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Tension in a string in free fall

A body is attached to another with a string and both are in free fall. How does the tension in the string being zero make sense conceptually?
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5answers
70 views

How does the sea level reach a fixed height?

Consider a flat body of water on the Earth. On all tiny elements of water in that body, the buoyant force is equal to the force of gravity due to Earth. Now if I introduce the moon to this body, (or ...
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4answers
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Principle of friction force

When two equal and opposite forces act on a body at rest or in motion we say it is rest or in its state of motion. But when a body kept on a table starts moving uniformly due to a force applied, it ...
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2answers
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What force is acting on a car?

We say acceleration is produced in a body when a force acts on it in some direction.When a car moves with acceleration and I'm an observer on ground.What force should I say is acting on the car?
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1answer
33 views

Why did this table tennis ball rise to the sky?

The nozzle makes the water flow through the upper part of the table tennis ball. If the angle and velocity of the water jet are well controlled, the table tennis ball will rise to the sky. The string ...
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1answer
39 views

Variation of Tension in a rope [on hold]

In the 1st picture we consider the tension in the rope to be the same on both the sides. However in the second picture we take it to be different. Why? If we have to consider a general case then why ...
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3answers
70 views

What happens to $P = F × v$ for a car moving on a frictionless surface and in vacuum?

I'm considering a scenario in which a car with an engine capable of producing maximum power of 200 hp is moving on a frictionless surface and in vacuum. Since no work is lost due to friction or air ...
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2answers
52 views

Acceleration of two bodies on an incline and the normal between them [on hold]

Question: What is the acceleration of each body, if they slip along the incline? What is the normal between them? Assume the incline to be frictionless and neglect air resistance. My teacher solved ...
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1answer
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Buoyant force when object is between two liquids

Suppose we have a ball floating in liquid A. Then we pour a liquid B on top of the ball (Assuming that the liquid is poured such that the ball doesn't oscillate) . The ball rises up. Why? According ...
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0answers
31 views

How can i calculate the upwards force applied by a water jet on a suspended sphere [on hold]

First of all, i would like to possibly clear a few things up: yes, i do know the weight of the ball, but i would like to be able to calculate the upwards force of the water jet on the ball. (hence, i ...
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4answers
52 views

Normal Force on an object on the earth’s surface

If a body is on the earth’s surface at equilibrium, the forces acting on it are gravitational (by the earth’s centre) and normal (by the surface). These balance each other and allow the body to ...
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0answers
20 views

How much more damage is caused after hitting a brick wall at 100mph over 50mph? [duplicate]

How much more damage is caused after hitting a wall at 100mph over 50mph? It is clear that there is just twice as much force generated after hitting a wall at 100mph, since the deacceleration is twice ...
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0answers
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Relative velocity and pseudo forces

If I am in a spaceship moving in deep space....... which is accelerating.... There is nothing around to compare my motion with.... How can I say even if I'm moving or not....if I say I experience a ...
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3answers
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Why doesn't a force perpendicular to the direction of motion change the speed?

It changes direction but not speed and this is proved in experiments. But is there any more "deep" reason as that space has isotropy and energy must be conserved per example?
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1answer
39 views

How much pressure does the water ring exert on the spacecraft when gravity is generated by rotation? [on hold]

We all know that the rotating spacecraft will generate artificial gravity. If there is a water ring along the wall of the spacecraft, the width of the water ring is b, the depth of the water ring is H,...
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2answers
51 views

Confused about forces acting in this simple statics problem

I'm trying to solve this statics problem to find the internal tension that results, in each member: It shows 3 idealised weightless rigid members hinged in a vertical plane, in an isoceles triangle. ...
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0answers
27 views

Manipulation with drag force [closed]

I have a problem to solve concerning drag force and its relation with velocity. The problem is following: A car of mass m is propelled forward starting from rest by a constant force +F. Use b for the ...
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1answer
48 views

What would you call shelves failing after being bumped by a forklift?

From the video in this question, you can see a bunch of stable shelves that are bumped by a forklift. This causes a domino effect, but unlike a regular domino falling over, there is clearly a buckling ...
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1answer
20 views

Lorentz force within a flux tube

I know the formula for the Lorenz force exerted on a point charge $q$ moving with velocity $\vec{v}$ is given by $\vec{F} = q\vec{v} \times \vec{B}$. Now consider the flux tube with cross section $S$ ...
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0answers
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What happens if you hit street furniture with a car? [closed]

would you be able to drive on or get stranded? I played GTA 5 and it takes a long time before the car is total loss after it has hit a lot of street furniture.
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1answer
39 views

Convert inertia formula to excel calculator

I've been looking at this question: "Weight" of moving object in a car collision but to be honest I can't get my head around how to work it out myself (I'm not a physics student!). What ...
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0answers
29 views

What would happen if all fundamental force of every particle is increased by 1%? [closed]

I've read that the everything in existence is made out of fundamental particles and the properties of molecules and everything that is made from molecules are based of the interactions between it's ...
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0answers
21 views

Finding force exerted on a turbine blade by water flow

I am trying to find the maximum theoretical rotational power of a turbine from the following quantities: $\omega$, $r$, $\gamma$, $I$, and $t$. This is in an experimental setting, not an assignment,...
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2answers
55 views

Can we define potential for all conservative forces?

I know that defining potential for non-conservative forces is not possible and we can define potential and potential energy for conservative forces only. But can we define it for all conservative ...
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1answer
78 views

Why do people think that rockets can thrust in the vacuum of space? [duplicate]

A force is required to change the momentum of the rocket exhaust which consists mainly gas moving out of the rocket chamber. People think that it is the rocket that pushes the gas out. If this were ...
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0answers
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Why does P = $\rho$gh seem to contradict equal accelerations of fluids in a closed U tube?

This is based on a problem. The closed U tube is as shown : I want to figure out time period of small oscillations if the liquid interface is slightly disturbed. My take : considering an ...
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2answers
32 views

Spring force potential energy and work done

Is the work done by external constant force = to potential energy stored in the spring. i.e. $Fx=\tfrac{1}{2}Kx^2$ But we know $F=kx$ but then $Fx = Kx^2$
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0answers
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Finding force from torque equation

I have read an article on electrostatics textbook that, $$\vec {F}= \nabla {\vec {\tau} }$$ Such as,the toraue equation on a magnetic dipole is $$ \vec\tau={\frac{{\mu}_0 m^2}{2\pi z^3} }\hat{z} $$ ...
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0answers
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How do I draw a diagram of the forces that create the “barndoor effect” (unbalanced torque) in rock climbing?

I have been asked to use a diagram that illustrates when a flag in rock climbing is necessary. I have no idea how to draw the forces involved in torque.
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2answers
17 views

Aerodynamic Force Decomposition

We know that aerodynamic drag is proportional to the square of the velocity of the incoming flow: $$D=kV^2.$$ If I decompose velocity into arbitrary orthogonal $x$-$y$ directions:$$V_x=V\cos\theta\\...
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2answers
31 views

Real Pulley and Newton's Third Law

In a real pulley with two masses hanging from either side, the pulley rotates due to a non-zero torque, which I understand is caused by friction on the rope. I understand that if each mass was ...
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1answer
26 views

maximal acceleration of a wheel-driven vehicle

I was thinking about the maximal acceleration of a bicycle, I found a similar question. What remains unclear is that I found two coefficients of friction, one for rolling and one for static friction. ...
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4answers
63 views

Work when there is more than 1 force

I know that for an object with an applied force, the work done is $$W = Fd \cos \theta.$$ I was wondering what would happen when there is another force (e.g. friction)? Is it better to say that the ...
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1answer
38 views

Force during collision would be very high, would it cause a very big damage? [closed]

So suppose a body of mass 10kg travelling at 5m/s crashes into a wall, the time of deceleration would be very minute, say 0.01 second, then the magnitude of deceleration would be $$\frac {0-5}{0.01} ...
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3answers
391 views

Regarding Goldstein's claim that $\mathbf{F} = \dot{\mathbf{p}}$

From Goldstein: ... The mechanics of the particle is contained in Newton's second law of motion, which states that there exist frames of reference in which the motion of the particle is described ...
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1answer
88 views

Lorentz force in superposition of two magnetic fields

When an electron with charge $q$ travels with velocity $v$ perpendicular to a magnetic field generated between two permanent magnets with field strength $B$ and no electric field, it experiences a ...
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1answer
30 views

Why do we have more than one texture?

Say I rest my hand on a wooden desk. My hand does not go through the desk because my hand is made up of atoms and as is the desk. The atoms in my hand repel the atoms of the desk when I rest my hand ...
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0answers
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Can the pressure term in the general thrust equation be negative?

In the general thrust equation, it looks like the pressure term can be negative if the ambient pressure is greater than the nozzle exit pressure: $$F=\dot m\cdot V_\mathrm e+\left(p_\mathrm e-p_\...
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2answers
76 views

How would you explain pressure to a school kid?

suppose there is a squarish block (height 2 m) 1*1 on a table and different forces are acting on it from top perpendicular to the surface on top .Suppose it is like one force is of 3N in the middle ...
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1answer
35 views

Question regarding stress, force, and area [closed]

I came across this question recently. I understand that stress = force/area. I understand that the total force is 8kN. So what I tried to do was substitute the values for Area given in the question ...
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2answers
70 views

Potential Energy equation is wrong as $mg$ force acting upwards (by us) and gravitational force ($-mg$) get cancelled and no movement is possible [duplicate]

In physics, the potential energy of an object is mgh. We say that the potential energy of an object is equal to the work done on it to make it reach that height. So the work done = mg h. Mg is the ...
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0answers
138 views

What Is The Connection Between The Planck Force And Black-holes? [duplicate]

This question deals with a unique case where the gravitational force at the event-horizon of a Black-hole can be expressed by The Planck Force acting at the boundary of a Schwarzschild envelope. If ...
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1answer
47 views

What is true about thrust?

Our book says the force acting on an object perpendicular to the surface is called thrust If two forces are acting on an object perpendicular to the surface both of them will be called thrust or the ...
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1answer
30 views

How do I know whether members are in tension or compression when using Method of Sections?

So we started doing structural analysis in my engineering class lately, and are doing trusses. However, I'm not quite sure how method of sections works conceptually. I'm getting the right numbers, but ...
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1answer
53 views

What is $mass \cdot jerk$, or yank?

So if Momentum is $m \cdot v$, Force is $m \cdot a$, and Jerk is $\frac{\Delta a}{\Delta t}$ what is $m \cdot j$? I've read that the name for this is yank, but I'm curious as to what it is ...
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2answers
43 views

Gravitational Fields

I've been trying to understand a bit more about how gravitational fields work. I am trying to understand what would happen in the following hypothetical situation: astronauts are on the moon, and ...
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4answers
115 views

What is the direction of gravitational constant?

Our book says: $$\vec F=\dfrac{GMm}{r^2}$$ If Force is a vector quantity, $G$ must also be vector quantity so what is the direction of $G$. I am a school kid please explain simply and kindly
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0answers
28 views

Dielectrics between charges

Why does inserting a dielectric of dielectric constant $k_e$ have an effect of increasing the distance from $r$ to $r+t(\sqrt{k} -1)$ in Coulomb's law of electrostatics (where $t$ is the thickness of ...
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0answers
24 views

Would you feel inertial forces if you were inside a precessing gyroscope?

If a gyroscope is placed orthogonality on an physical axis which is paralel to a gravitational field if you're in a reference frame of the gyroscope do you have to modify Newton's law?