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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Field line Direction and exerted force

Magnetic field lines of a magnetic field have different directions. What information about the force exerted on a charge will give us the direction of field lines?
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Force on a magnetic dipole due to a magnetic field

Imagine a solenoid which has current $i$ and is producing a magnetic field $B$ which equals $$B=\mu N i$$ Now, imagine we put a small cylindrical magnet at the end of the solenoid. Then because at ...
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4answers
70 views

Why aren't things massless when they have balanced forces acting on them?

Since $0$ divided by anything is $0$, why isn't everything with a net force of $0$ massless? Since $F = ma$ rearranges to $m = F/a$, when $F = 0$, $m$ should equal $0$, shouldn't it? This obviously ...
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1answer
92 views

Newton's Third Law As Discussed in Den Hartog's Mechanics

A question, but some preliminaries in order to avoid answers involving concepts not yet introduced in the text I'm reading--Den Hartog's Mechanics. Near the very beginning of his book, Den Hartog ...
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1answer
51 views

Conservation of momentum always? [closed]

Consider two atoms A and B, with A at rest and B in motion towards A. As soon as B is in the atomic field of A, will it stop with its energy going into B or will it just move up to a postion where ...
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2answers
79 views

Confusion with $F=-\nabla V$, $F$ conservative

I am rather confused by the relationship $F=-\nabla V$. If a pen drops from a height it loses potential energy so $\nabla V$ is negative. From the above equation this means that the gravitational ...
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1answer
82 views

Newton's third law at the quantum level? [closed]

let's look at force at the atomic level to understand the newtons third law of motion. I'll use Helium atoms as an example. Now imagine we start with one atom HE2 stationary, and throw another atom ...
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34 views

Forces acting on a jet pilot [closed]

I found the forces at A and C with no problem, when it came to the forces at B I found the normal force of the seat on the pilot but the forces in the tangential direction got me. The solutions ...
2
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1answer
55 views

Why Vehicle's Engine back wheel driven? [closed]

Why most of the vehicles Engine Driving the Back wheels instead of Front Wheel. Including Cycle,two wheeler, bus, Car, Heavy Vehicles, I am guessing some science is there behind this, I dont know what ...
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3answers
56 views

Measuring force of a punch

I'm trying to build a device that can mesure the force of a punch. ​ My initial plan was to build a platform with 4 springs (one at each corner) and an accelerometer in the middle. But, if the ...
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2answers
38 views

Why can't a force between two particles exert a torque?

Let's say I have two particles which exert a mysterious force between them. Say they lie on the x-axis. Newton's 3rd law tells us that the force on the two particles due to the other must be opposite ...
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4answers
242 views

How many legs (minimum) would a chair need in 4 spatial dimensions for you not to fall?

I was reading another post in physics.SE about chairs when this question arose. My guess is we would need more than in 3 dimensions as in 2 dimensions you would just need 2 (I think). I've been trying ...
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1answer
55 views

Seesaw Physics - Shipping Container House Problem

I'm currently building a house using shipping containers. One of the containers is in a cantilever position, sticking out from the base concrete structure like this: ...
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2answers
84 views

When I move while holding a book, why is work done zero?

Now this question has many answers all over the internet, but this site gives me the power to pose my doubts in front of you all. Let's get straight to it: Suppose I move on a road while holding a ...
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1answer
18 views

determine force from a hammer to pull out a nail

Hi the force from the hammer is 5,4 * F according to my book .. How did they calculate that ? Should not it be 27 * F thanks
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11answers
22k views

Why are four-legged chairs so common?

Four-legged chairs are by far the most common form of chair. However, only three legs are necessary to maintain stability whilst sitting on the chair. If the chair were to tilt, then with both a ...
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1answer
98 views

Is it possible to pull a car at a constant speed?

Suppose we use a trailer to pull a car, which has a damaged motor. The car moves at a constant speed, assume that air drag is negligible and the wheel does not slide on the road, it only rotates. ...
2
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2answers
154 views

Newtons third law with two charged particles

Imagine we have two charged particles, $q$ and $Q$. $q$ is at rest at a point and $Q$ is moving with a velocity. Now $q$ is exerting an electrostatic force on $Q$ and $Q$ makes a magnetic field but ...
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0answers
19 views

Magnitude of resistant and buoyant force exerted by water on tank

A tank has mass $1.7\times10^8\ \text{kg}$ and its engines generate a forward thrust of $7.4\times10^5\ \text{N}$. Determine resistive force exerted by water. Determine magnitude of upward buoyant ...
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1answer
43 views

Why is the potential energy minimal when the repulsion and attraction force between molecules is 0?

According to this potentialcurve and the other curve(?) the potential energy is minimal when the intermolecular forces equal zero. Why? How should I interprete negative potential energy in this ...
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1answer
60 views

Which system's mechanical energy is conserved?

As the figure shows, $m$ starts falling down from its current position at the original speed of zero. And $M$ is a curved side trapezoid. All friction can be ignored. |# <- This hash stands for ...
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4answers
36 views

Confusion regarding the forces in a system of particles

I think the internal forces in a system of particles is zero. But is it possible for the sum of internal forces to be non zero in any case?
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1answer
58 views

Two mass spring system

The equations of motion of the spring mass system with, m = 1 $ \ddot{y_1} = -k_1y_1 + k_1(y_2-y_1)$ $ \ddot{y_2} = -k(y_2-y_1) - ky_2$ My question is with the second term in the first equation. ...
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1answer
37 views

How much mass should be removed from balloon

If a hot air balloon has a mass of 310 kg and it is motionless due to an upward buoyant force, how much weight should be removed to obtain an acceleration of 0.15m/s^2 upward. I am not sure how to ...
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2answers
40 views

Why don't barbells tip over when a 45 is placed on one side?

A standard barbell is 45 pounds, as is the heaviest weight available in most gyms. When a weight is placed on the side of a barbell, some of the barbell is to the "outside" of the weight, like so, so ...
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3answers
70 views

If I walk forward and stop was there work done?

If I'm on a flat surface and I start walking and go to a constant velocity, then I slow myself back down to a stop, was there work done? I would think the answer is no because $work = force * ...
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0answers
23 views

Relationship between magnetic force acted upon a diamagnetic substance and the magnetic field applied to it

I have a sample of bismuth that I have applied a measured B-field to through the use of a solenoid electromagnet. I've been trying to find a formula relating the B-field to the force that the bismuth ...
3
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1answer
43 views

How are orbits made stable

I understand the concept of object staying in some orbit due to centrifugal force and gravity. However I do not understand how is orbit of a body like satellite or planet has perfect balance between ...
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2answers
98 views

Why does Conservation of Momentum fails because of friction? [closed]

I did this experiment in my lab. We had two cars with wheel connected by a string. One car has a spring that can be triggered by a switch at the top of the car. (Frictionless surface and light string$ ...
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2answers
66 views

What causes the balloon to pop when we push with needle onto it's surface?

I am a bit puzzled because I can see two possible reasons, first one is more common and the other one makes sense too, so here they go: 1) balloon pops because of the fact that after pressure is ...
3
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1answer
388 views

Lifting a wet object off a table

When there is a film of water in between an object and the tabletop it rests on, it is difficult to pull the object directly upward. However, when you slide the object, it comes off easily. What is ...
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0answers
31 views

Tension on wire holding open door, using moments about a hinge? [closed]

Using moments about the hinge, what is the tension in the wire holding the door open? The wire is horizontal. The door is 5m. See diagram: The door is at tan inv (3/4) : 36.9 deg to the ...
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1answer
23 views

Force from a large conducting plate [closed]

How can I find the distance to a test-charge, hoovering below a conducting plate? Newtons laws applies. $$ $$ According to this information, I conclude that the force is equal zero. It is not ...
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2answers
51 views

Direction of static friction in inclined rolling motion

I can't seem to understand in which direction static friction faces for inclined plane motion with rolling motion. This considers rolling motion without slipping, how do i find the direction of the ...
0
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2answers
52 views

Inertial forces and centre of mass

Is inertial force always attached to the centre of mass of the object? Why? What rules cause this to happen? See the example below of the leaned bike in a corner. The force $m\frac{v^2}{r}$ ...
2
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1answer
67 views

Missile-like trajectory calculation [closed]

First of all I want to let you know that I'm not a Physicist, I am a Video Game Developer. I can simulate physical and mathematical equations and can also use some built in physics. For example I ...
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2answers
48 views

Distinguishing real forces and fictitious/pseudo forces in Newtonian mechanics

In understanding the law of inertia I had to consider the motion of bodies screened from the so called "real forces". What characterises these real forces? What makes us call them real? Or what is ...
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0answers
28 views

Force required to move a stationary object [closed]

What force would be required to move a vehicle 20 feet. The vehicle weighs 5000lbs the brakes are engaged on all 4 wheels during this event.
2
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1answer
49 views

Is there any way to justify or derive the form of the Lorentz force from relativity theory?

Lorentz force is in this form: $$\vec{F}=q[\vec{E}+\vec{u}\times\vec{B}]$$ As we know, it is Lorentz-invariant. Is there any way to justify or derive its form from relativity theory?
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1answer
59 views

The nature of Newtonian laws of motion

The first law of inertia deals with the motion of "ISOLATED BODIES".. What are these isolated bodies? How do we know that a body is free from all forces? and eventually What do we mean by forces ...
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2answers
58 views

Why can we assume, when dealing with tension, that the mass of a rope is $0$ but still assume that there are forces on it?

I started studying tension and I can't understand the following concept: If I have two objects $A,B$ collegated by a rope, where $A$ applies a certain force $\vec{F}$ on it, I would have that the ...
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0answers
31 views

How can light be used to move an object [closed]

If light can push an object, what would have to be done with it to push a 1lb. square object across a polished surface?
1
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1answer
47 views

Relationship between applied and normal force?

After watching and reading many explanations on friction, normal force and newton's laws, I am more confused than I was before... I have a simple question: Why is the normal force of an object that ...
1
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1answer
68 views

In perfect vacuum (no external force), if I apply a small amount of force to a body, will it continue to accelerate forever?

According to the equation F = ma, the greater the force applied to a body, the more is it's acceleration. But in a place where there is no gravity or any other kind of external force, If I apply a ...
0
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0answers
21 views

Does nature prefer second order differential equations? [duplicate]

We all know Newton's second law: $m \ddot{x} = F(x)$ or equivalently Euler-Lagrange or Hamilton's equations. In quantum mechanics the Schrödinger equation is also a second order differential equation. ...
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1answer
52 views

Gravitational Potential Energy misunderstandings [closed]

I'm really confused by the derivation of Gravitational Potiential Energy. I took a screenshot of the wikipedia entry below. My major confusion lies in: 1. The use of the position vector r in the ...
2
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0answers
66 views

Gravitational field due to inner shell on the outer shell [closed]

There're two uniform hollow shells of radius $R$ and $2R$ each. The one with radius $R$ is inside the larger shell touching the larger shell's inner surface and its center. What's the net ...
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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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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 ...