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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 ...

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What is the Gravitational force between 2 bodies, when their centres of mass coincide?

According to Newton's Universal Law of Gravitation, $F=G{\frac{Mm}{r^{2}}}$, where $M$ and $m$ are the masses of the two bodies, $F$ is the force of attraction between them, $r$ is the ...
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0answers
19 views

How to find ground reaction force for dynamic rigid body?

I have a model of trebuchet (a siege engine). I consider its motion when it has 2 degrees of freedom $\gamma, \varphi$ - this is when a projectile $m_{D}$ is propelled on the ground. I want to know ...
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28 views

Coulomb's law: Torsion balance experiment

I have read about Coulomb's torsion balance experiment for the first time from an online pdf article. I interpret it as follows: Black ball $-$ neutral Red ball $-$ positive charge Blue ...
5
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5answers
388 views

What is $R$ in the formula for escape velocity?

From the escape velocity formula $$v_e = \sqrt \frac {2GM}R.$$ Some sources say it is the distance between two objects with mass $M$ and $m$. Some examples I have read, only used radius of the $M$. ...
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1answer
58 views

How to calculate speed of buoyant object rising

I'm looking for a formula to calculate the speed of object in buoyancy. Is there any formula available for this purpose? For example, if I release one liter water bottle from under 10 meter distance ...
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1answer
35 views

Physical meaning of same pressure on the same plan (hydrostatic paradox) with different weight above them

In this picture the points on red have the same pressure because the weight of the fluid is the same above them. But according to pascal law the point on black must have the same pressure(both 3 ...
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1answer
58 views

Factor $1/2$ in work done by spring force [duplicate]

My book says Spring Force = $-kx$ where k is spring constant and x is displacement from equilibrium position. Then it says work done by spring force is $-kx^2/2$. But I know Work Done = Force $×$ ...
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2answers
50 views

Why the resultant spring constant different in the following two cases?

In these two cases in the first case my book The Physics Of Waves And Oscillations by NK Bajaj says: That the restoring force exerted ...
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2answers
35 views

Wind dynamics: preventing a banner structure from blowing over

Background I'm the co-chairman of a local 4k race. This year, we have a new truss structure (very similar to the one pictured below) with a banner that will be serving as our finish line. After some ...
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1answer
39 views

Dependency of kinetic friction

1.Why kinetic friction doesn't depend on speed of object? Also explain why static friction > kinetic friction > rolling friction? 2.when we keep a book on a table , the table is said to exert a ...
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0answers
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Force and kinetic energy [on hold]

Two bodies A and B lay motionless on a frictionless surface. Mass of A is smaller than the mass of B. There are two equal, constant forces acting on the bodies along the same straight distance d. ...
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3answers
2k views

Why is the work done by a rocket engine greater at higher speeds? [duplicate]

From this comment by orlp: If I strap a rocket booster to a rocket in space and fire it for one second, then the work provided is much higher when the rocket is flying fast compared to when the ...
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0answers
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Calculating the force without the mass [on hold]

How to calculate the force if you have just the time and speed? Example: •Calculate the force of the brakes of a car who has to stop in 5 seconds at the speed of 72km/h.
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4answers
145 views

Axis of rotation of the body [on hold]

A couple is applied to a rod such that the forces are at equal distance from the centre of mass of body. The body will rotate about an axis through its centre of mass. However, if the couple is ...
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0answers
44 views

Components of coriolis force [on hold]

$$ \color{black}{ \begin{array}{c|c|c} % START: Column Labels \begin{array}{c} \textbf{Object's} \\ \textbf{direction} \end{array} & \begin{array}{c} \textbf{Horizontal} \\ \textbf{...
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1answer
37 views

Where does the energy come from when a magnet moves a compass? [duplicate]

My very limited understanding of magnetism is that it is essentially stored energy. However what I'm confused on is about the following situation: If you have a compass and you move a magnet close to ...
2
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1answer
81 views

According to newton's laws, why do the two different masses of an Atwood machine move in opposite directions?

Consider an Atwood machine with two different masses $M$ and $m$ such that $M > m$. When trying to find the acceleration of that system, all solutions I've found go like this: There are 2 forces ...
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2answers
44 views

Non-zero torque for a part of rod in equilibrium?

Suppose a vertical rod of $L$ length has force $F$ acting towards right, on top and bottom positions. A force $2F$ acts towards left on the centre of rod. The body is equilibrium. Let's take the lower ...
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1answer
27 views

Free body diagram of a liquid molecule [on hold]

Atmospheric pressure is the weight (Force) of the air per unit area. What will be the free body diagram of a water molecule be on the top of a liquid taking atmospheric pressure and vapour pressure ...
0
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2answers
44 views

Objects in space [on hold]

If an object is set in space, will it move away from its location? Say a space station. Without any kind of thrusters, would it stay where it is, or always be moving off location?
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2answers
50 views

Dominoes falling on each other

If i exert a force $\vec{F_1}$ on a domino it would fall onto the second hitting it with a force $\vec{F_2}$, my question is : Would $\vec{||F_2||}$ be equal to $||\vec{F_1}|| + m.a$ or would $\vec{...
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2answers
52 views

What happens if we apply different forces in opposite directions on both ends of a spring?

I'm confused about this... If I have a spring and I apply force F1 towards the right on the right end and F2 towards the left on the left end, what will happen? There are no blocks, just a light ...
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9answers
5k views

Why does work depend on distance?

So the formula for work is$$ \left[\text{work}\right] ~=~ \left[\text{force}\right] \, \times \, \left[\text{distance}\right] \,. $$ I'm trying to get an understanding of how this represents energy. ...
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0answers
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Impulse or Force of a stream [closed]

Let's take a water stream which has $0.5\ \rm m^2$ of area and a liquid such as water moves through this area with a velocity of $1\ \rm m/s$ so what would be the impulse or the force of the water ...
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3answers
73 views

Is there any naturally occurring downward force that exists on Earth other than gravity? [on hold]

For a project, I was wondering whether or not it is possible to increase the net downwards force acting on an object so that you are able to manipulate its weight.
2
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1answer
45 views

Are two charges attracting each other constantly accelerating?

Using Coulomb's Law: $\frac{k_eq_1q_2}{r^2}$, say we have $2$ charges of $1\ \rm C$ each, separated by a distance of $1\ \rm m$. The force would be $8,987,551,787.3681767\ \rm N$, considering $k_e = ...
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3answers
31 views

Why is the internal pressure against the nozzle body not included in calculating the anchor force?

Why is the internal pressure against the nozzle body not included in calculating the anchor force? The attached picture shows all of the forces acting on the body. But I would assume the pressure on ...
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2answers
89 views

How did Newton know that there is force between two mass? [duplicate]

Newton's Law of Gravitation states: $$F=\frac{GM_1M_2}{r^2}$$ How did he recognize that there is a force between two masses?
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2answers
56 views

Physical meaning of variation of force of pressure with altitude in fluid

We usually prove that pressure is a function altitute Z. Imagine a cube in a fluid, then the force of pressure on the bottom surface is higher than the force of pressure on the top surface. But we don'...
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1answer
35 views

How a particle move with a constant velocity from rest? [closed]

How can a particle move with a constant velocity from rest? I know that the net force on a particle that moves with a constant velocity is zero, so how will it move from rest with a constant velocity ...
1
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2answers
57 views

Moving a charge with constant velocity

How can we make a positive test charge move with a constant velocity from infinity if the source charge is positive? I know that when a particle moves with a constant velocity velocity the net force ...
0
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0answers
24 views

A box is pushed on a rough surface [closed]

The question reads that someone is pushing the object at a constant velocity before letting go. It then asks to describe the motion after the pushing stops. I put that the box moves at the same speed ...
2
votes
2answers
116 views

Why is torsional shear for a circular cross-section maximum at the biggest radius

Equation: Tao = (T*C)/J i know the equation but it just seems counter-intuitive that the maximum shear stress is at the biggest radius for 3 reasons that I have(thought of). 1- imagine/assume that ...
2
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1answer
24 views

If magnetic induction vector will not be perpendicular to charge velocity, there will be work?

The work is $A=FS$ The force is $F=q[E+v\times B]$ The $v \times B$ is a new vector, $|v||B|\sin\space \alpha$ Let's consider the next case: Where red dot is a particle, moving due to $v$. We do ...
2
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2answers
112 views

Susskind & Hrabovsky: For any system $F_i=-\partial_{i}V$?

In the following $\left\{x\right\}$ means a configuration point in $3N\text{-dimensional}$ configuration space. Each $x_i$ represents one coordinate of one particle of the system of $N$ particles. ...
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0answers
40 views

When does a car engine do more work? From still to 50kmh or from 50kmh to 100 kmh [closed]

A car accelerates from rest to 50 km/hr and then from 50 km/hr to 100 km/hr. Assume there is no air drag. In which case does the engine of the car do more work?
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1answer
30 views

Acceleration value if coulomb's force equals to 0?

If i have a point in an electric field where the coulmb's force is equal to 0 does this mean that the acceleration and the velocity of the charge q in the mentioned point are also equal to 0? In this ...
1
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1answer
90 views

Is it possible to create weighing machine with water indicator

I want to create a weighing machine that works with water. After researching on Google I got this. $1$ $\text{cm}^3$ of water weights $1$ g. So, with that equation I'm planned to create this below ...
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2answers
69 views

Stress/strain within an object experiencing a single applied force

If I push an object in space, will any strain/stress happen within the object, though there is only 1 force rather than a pair of opposite forces on the object? Can be any (even if trivial) stress/...
0
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1answer
36 views

Could space repel mass?

I'm not an advanced physics person, so any explanations need to be reasonably low-level... I was looking at oil/water bubbles (hydrophobic vs hydrophylic molecules) and it got me thinking about the ...
0
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1answer
29 views

Spring Constant of Two-Sided Fixed Beam [closed]

Let's suppose I have a two-sided fixed beam: ...and I want to find the equivalent spring constant... can I do the following: I know that the maximum deflection (at the center is): $$\delta =\frac{...
1
vote
2answers
36 views

Force, work and the apparent disappearance of Mechanical Energy [duplicate]

A man exerts force on a wall of bricks. The man must have consumed the energy he possessed (mechanical energy?) to exert the force. The man sweats and tires himself out but the wall does not move. ...
0
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3answers
64 views

Actual mass and Apparent mass due to Force

Suppose a block is placed on a surface (with a non-negligible frictional constant) and a person exerts a constant force $F_1$ on it parallel to the surface. Whether the force is able to cause ...
0
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1answer
89 views

How did scientists before Coulomb ensured this fundamental property of magnets? [closed]

Firstly, please note that I am talking about the period BEFORE electricity and magnetism were unified. So I am NOT seeking for answers based on Ampere atomic current model of magnets. I have read the ...
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2answers
39 views

From Where Did The Table Get Energy? [duplicate]

When a block in resting on a table (the table is on Earth) the table stops the block from going more down, from where does it get the energy to apply a force opposite to gravity?
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2answers
88 views

Relationship between acceleration due to gravity and mass [closed]

See http://www.feynmanlectures.caltech.edu/I_07.html: "This statement can be expressed mathematically by the equation [...] If to this we add the fact that an object responds to a force by ...
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1answer
29 views

Forces From Opposite Sides On A Block

Suppose we have an indestructible box in space , and we apply equal forces on two opposite side of box , the box wont move but then where will the energy go?(Conservation of energy)
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3answers
50 views

Force without acceleration?

Suppose we have a metal block tied to a rope at a certain height and below it is a magnet,after some time we bring another magnet ,the rope doesn't break but was there more force applied on the metal ...
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1answer
56 views

Work done by moving a body moving on a circular path [closed]

A body moving in circular path of radius $8\sqrt{2}m$ is acted upon by force: $-y\hat i +x\hat j$. Find work done by its complete revolution. So I was trying this question and I could solve it in ...
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0answers
27 views

NEWTONS 3 LAW OF MOTION VOILATED [duplicate]

*how can we push some object according to newtons 3 law it states that every action have an equal and opposite reaction but what happens to object when i push it and it moves how newtons 3 law ...