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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4
votes
0answers
34 views

How can a bowling ball curve in both directions?

There is a popular video on facebook that I just don't understand. A man spins a bowling ball very fast then slightly taps it down the lane. Somehow it does half of a figure eight, curving around two ...
-3
votes
1answer
52 views

Do you say it right? [on hold]

If someone asks you your WEIGHT what would you answer in SI Units. My weight is x 'kilogram' My weight is x 'Newton'. As we know that weight is a force due to local acceleration and still most ...
1
vote
1answer
21 views

Does a capacitor experience a Newtonian reaction when being charged?

Say I have a capacitor that is being charged with a battery. There are two wires, one on the positive and one on negative terminal of the battery which go to a capacitor. During the charging, a ...
2
votes
2answers
31 views

Glass tube diameter to hold water when turned upside down

If I have a glass tube that is closed at one end and has length l, how can I find the range of diameters that the tube must be so that the water does not fall out of the tube when the tube is turned ...
-3
votes
0answers
23 views

Calculating fields of two magnets [on hold]

I want to use two NEODYMIUM IRON BORON permanent magnets to create a repulsion between them. In which one PM is attached to the robot (which has three wheels and its weight is 5KG) and the another PM ...
10
votes
2answers
591 views

Why does electric force depend on the medium?

Comparing the equations for the gravitational and electric force $$\vec{F}_g=-\frac{Gm_1m_2}{r^2}$$ and $$\vec{F}_e=\frac{Kq_1q_2}{r^2}$$ I noticed the only major difference between them is that ...
0
votes
0answers
46 views

Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
1
vote
3answers
172 views

Where Potential increase gets it's energy from?

Imagine there are two particles: A,B; of which, we observe A to be stationary, while B is moving towards A at velocity v. A,B has same mass; and they are charged both positive. B has a potential wrt ...
0
votes
1answer
41 views

Path of a swinging object on a rope [on hold]

With my lanyard in hand (weighted by my keys), a gentle swinging motion will put the keys in pendulum motion, swinging back and forth. Pendulum motion is relatively easy to model since it is ...
-2
votes
0answers
28 views

Downforce formula [on hold]

I need a formula force calcuating the down force generated by a NASCAR. I have done research and found some answers on google but i don't know what the formulas mean. So i was wondering if any body ...
2
votes
3answers
61 views

If I push my hands against each other, why does the stronger one move the weaker one if the forces should be equal and opposite [duplicate]

If I were pushing my hands against each other, the stronger arm will move the weaker arm, but if all forces have an equal and opposite reaction, why does the weaker one move?
2
votes
1answer
52 views

Would the Moon be able to take water from Earth?

I know that if you add mass to the moon, it would get closer to the Earth. We all know that the moon causes the tides because it's gravity pulls the water. So, my question is: If the moon gained more ...
1
vote
0answers
41 views

How does the gradient operator pick up a minus sign when the reference frame is switched from one particle to another? [on hold]

A potential between two particles, $i$ and $j$, is given as a function only of the separation distance, $$V_{ij} = V_{ij}(|r_i − r_j|)$$ It should follow that the force by $j$ on $i$ is equal and ...
4
votes
3answers
110 views

Which force to resolve?

In the above image the particle is effectively moving 'out of the page' in circular motion. We want to solve for $\alpha$, the slope is smooth, and the particle is moving neither up nor down the ...
1
vote
1answer
49 views

What makes cart with a moving object in it gain speed (no friction anywhere)?

I would like to understand what makes the cart below the moving object move. There is no friction between any of the objects. The cart is moving therefore there is force applied to it. The only force ...
0
votes
1answer
15 views

Resultant force and constant velocity

Let's say for example, Jack is pushing on a box with force $F$, and John is pushing from the opposite side with force $F$ as well. We say that there is no resultant force, and the box remains stable ...
0
votes
1answer
24 views

Massless rope in a pulley pulled by a person

A massless rope passes through a pulley. On each end of the pulley there is a different mass (object). A person grips one of the masses and thus the system comes to equilibrium. How would you ...
1
vote
1answer
29 views

Does the shape of a containter affect the apparent mass of liquid inside it when measured by a scale? [duplicate]

For both containers it is true that: $p_{bottom}=p_{atm}+\rho gh$ and $F_{bottom}=a*p_{bottom} \iff F_{bottom}=a*p_{atm} + a\rho gh$ I do not know how a scale functions, but I guess that the only ...
1
vote
4answers
70 views

Negative friction force, positive normal force

I realize that formulas don't always tell the whole story, but there seems to be some information missing from the equation: $F_f=\mu F_N$ Imagine we say up and right is positive. Then if an object ...
0
votes
2answers
36 views

Objects and forces: air resistance

A force always works between two objects. When we are talking about air resistance acting on a skydiver for example, would air be considered the second objects besides the skydiver?
0
votes
3answers
48 views

Conditions for the tension to vary in the rope

What are the conditions for the tension to vary in the rope. I have read below conditions 1. rope has to have some mass 2. rope is accelerating I get the 1st ...
-1
votes
0answers
27 views

Force required to swing gate open/close

I need to know how to calculate the force required to swing the gate open / close. If it is moving straight, we can use f=ma, but how to calculate for swinging motion? When I open or close the gate, I ...
0
votes
1answer
34 views

Doubts About Force and Inertia!

But then what does inertia mean at all!? Cant we calculate how much it resists the applied force? I mean considering an imaginary plane with no friction but gravity as of Earth and an enormous mass of ...
0
votes
0answers
36 views

Constant Velocity and Forces [closed]

I understand that if an object is maintaining constant velocity, then the net force is zero. With that said, the force due to friction equals the applied force, right? What if you were to diagram ...
0
votes
3answers
31 views

Effect of internal force on the weight of an object

A man is holding a closed cage on the palm of his hand with a bird in it. When the bird flies with an upward acceleration inside the cage, it feels heavier. But the force due to the bird in the cage ...
1
vote
1answer
35 views

Might one fall out of a basket swing?

My nieces like being pushed high in a basket swing. My sister-in-law worries they will fall out. Assuming I don't push them above horizontal, that I don't catch the basket and stop it mid-swing, and ...
-2
votes
1answer
71 views

Boeing 737 Homework Problem [closed]

I have done the above problem, but have come out with a rather large surface area. Could someone point out my mistake(s)? Given/Assumptions: I assume $\sum F_y=0$ because it's level and straight. ...
1
vote
0answers
23 views

What forces act on a caravan being towed by a car? [closed]

What forces act on a caravan that is being towed by a car? How does this compare to a simple car travelling at a constant speed?
0
votes
3answers
49 views

Tension in rods (basics)

I have a problem understanding these basics. What is the tension in the ground rod due to the forces exerted by the slanted rods? Please feel free to correct me at any point. Rods are idealized ...
0
votes
2answers
30 views

Magnitude of Tension: Circular Motion [closed]

Please consider the following: A tennis ball connected to a string is spun around in a vertical, circular path at a uniform speed. The ball has a mass m = 0.165 kg and moves at v = 4.76 m/s. The ...
1
vote
0answers
21 views

Calculus formulas for buoyant force?

I am launching a high-altitude balloon as a part of a physics project I am working on. I know that the amount of helium I need corresponds to about 40 newtons of lift for the launch, which is all I ...
0
votes
4answers
74 views

When writing a differential equation, when do you take $+\text{d}x$ and when do you take $-\text{d}x$?

When writing a differential equation I'm confused as to when to write $+\text{d}x$ a and when to write $-\text{d}x$ a where $x$ represents some quantity. For example, I wanted to derive the equation ...
0
votes
1answer
26 views

The equation for average impact force over distance traveled/penetrated equals work done/change in kinetic energy [closed]

So the equation Favg * d = Work or change in kinetic energy, is this true? If a car crashes into a tree by 1 meter with 10000 joules, is the impact force on the car 10000 Newtons? If a bullet ...
0
votes
1answer
20 views

Why, here, the torque with respect to bob is zero?

here, as you see, is a diagram of a pendulum with moving pivot along x-y surface. This picture was obtained from a journal in which this equation was written: $$F_x l \cos\theta = F_y l \sin\theta ...
1
vote
0answers
31 views

Centripetal force at the pole is different from the equator

why is the centripetal acceleration in the poles and equator if different? I know that it's related to Equatorial budge. But what I don't get it is that the centripetal force is zero at the poles. ...
0
votes
1answer
41 views

Why the force acting on a particle is the negative gradient of a scalar potential? [closed]

For conservative forces we can proof that it is a gradient of a scalar potential, but why we use the negative sign? In every book I searched, it said that it is like an agreement between physicists, ...
0
votes
1answer
35 views

Wind resistance [closed]

You have a metal plate/sign (max weight $5\, \text{kg}$) $1200\, \text{mm}$ long and $400\, \text{mm}$ high pivot/hinge at its base. A windspeed of $90 - 100\, \text{km/h}$ is applied to one face of ...
1
vote
2answers
44 views

Question about Kinetic Energy and Force acting on a body

Below is the graph of a body that rests on a friction-less flat surface. On this body force F is applied and it's value is being depicted in the graph below. We can see that the body moves from point ...
2
votes
1answer
45 views

two spiring balances

My 9th grade textbook says when we set a apparatus by the following procedure "tie the free end of two spring balances X and Y together and name this intersection A and then fix the rigid end of ...
2
votes
0answers
23 views

Could a hydrophobic surface increase a liquid's resistance to compression/displacement?

Imagine a quantity of an aqueous (yet slightly viscous) solution is resting on a hydrophobic surface with a contact angle around 100°. A downward force is then applied as a (repellant) surface is ...
1
vote
2answers
66 views

Why do the masses in an Atwood's machine move?

The masses you see on the following picture are $m_1=8$kg and $m_2=12$kg. Also the coefficient of friction between $m_2$ and the floor is $0.25$. What i'm concerned with is that although $m_2 ...
1
vote
0answers
12 views

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?
1
vote
0answers
13 views

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 ...
3
votes
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 ...
2
votes
1answer
91 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 ...
0
votes
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 ...
3
votes
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 ...
1
vote
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 ...
1
vote
0answers
32 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
votes
1answer
54 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 ...