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 ...
7
votes
3answers
5k views
How does the 'water jet pack' work?
So I was cruising around at YouTube and saw this sweet video, and as I was watching started to wonder: "How is this possible?".
For a little bit of background, in case you decide to not watch the ...
0
votes
1answer
91 views
Energy needed to lift and bring down an object
A mass of 0.5 Kg needs to be moved from point A to another point (B) which is 1 meters above point A. The time for this movement should be 0.2 seconds, then the mass is kept at position B for another ...
0
votes
0answers
17 views
Force being applied to an object [closed]
I am working on a project and I do not have a clue about Physics. I have a 3400lb,1542kg object traveling at 210mph. When it is stopped by another object that is not in motion, what is the force of ...
2
votes
3answers
586 views
Example in the book: A simple accelerometer
A simple accelerometer
You tape one end of a piece of string to the ceiling light of your car and hang a key with mass m to the other end (Figure 5.7). A protractor taped to the light allows you ...
7
votes
3answers
145 views
Where does the extra equation come from to determine the forces from an object on a table?
I have a question about basic statics but somehow I cannot manage to find the answer on my own (btw, this is not a homework. It's been so many years since school for me...).
The problem is very ...
0
votes
1answer
29 views
Inclined plane question
An object, mass $m$ is placed on an incline, angle $\theta$. System is at equilibrium. coefficients of static and kinetic frictions are $\mu_s$ and $\mu_k$ respectively. Then:
1) What is the Total ...
3
votes
2answers
471 views
Ski Jumper's vertical velocity after 246.5m record?
What would be the vertical velocity of this ski jumper (ski flyer), after he first touches down, after he breaks the record with a 246.5m jump? What g force would he experience as he slows down?
...
10
votes
5answers
534 views
Why do we still need to think of gravity as a force?
Firstly I think shades of this question have appeared elsewhere (like here, or here). Hopefully mine is a slightly different take on it. If I'm just being thick please correct me.
We always hear ...
1
vote
0answers
37 views
Why the screwdriver roll?
I am trying my level best to give this screwdriver a vertical push only, but it is going in a circular path. I thought of uneven friction due to non-uniform normal reaction...what do you think? I have ...
0
votes
1answer
148 views
Force due to combination of free space and dielectric
I will make a generalized form of my question.
There are two point charges $q$, $x$ distance apart.
And there is a dielectric slab of thickness $t$ and of dielectric constant $K$.
Should the force ...
2
votes
1answer
18 views
Magnetic Force on a Loop and number of turns
Suppose we have a rectangular current-carrying loop with current $i$, then we know that the magnetic force on each side can be found as:
$$F=iL\times B$$
Where $L$ is the vector in the direction of ...
-2
votes
1answer
40 views
A double-sided lever and multiple forces [closed]
Assume a double-sided lever where the left arm has a length of a and the right arm has a length of b + c. Please refer to this ...
0
votes
0answers
28 views
electrostatic repulsion [closed]
Consider a homogeneous ring of radius $R$ made of a thin wire of cross section $A$ with $R^2≫A$. A charge $Q_1=10\mu C$, uniformly distributed over the ring, broke it apart due to electrostatic ...
0
votes
1answer
25 views
Kinetic energy when $F(t)$ graph is given
The very basic problem here is that the point where this graph ends is ambiguous. I mean, what is the corresponding $y$-value for the point whose $x$-valu is $4.5s$? Then I think we should find the ...
0
votes
1answer
160 views
Deceleration of Vehicle off pavement
How would I calculate the deceleration of a vehicle (ATV), wheels locked, on dirt? How long would it take to halt? How fast is it decelerating?
I used this calculator, but it seems incorrect for a ...
2
votes
1answer
68 views
Convert a 200mm linear stroke into 90 degrees motion
Can anyone help me Convert a 200 mm linear stroke into 90 degrees motion with as much mechanical advantage as possible or into two 90 degrees motions with as much mechanical advantage as possible?
...
0
votes
1answer
115 views
Opposing forces on an air cylinder
If an air cylinder is pushing two platens apart with a force of 100lbs, do the platens need to push back at 100lbs or 50lbs each to keep the cylinder from moving? Assume no friction and both platens ...
2
votes
2answers
65 views
Intuition contradicting answer for calculating pressure
I have a cylindrical container say of some base area $A$. The atmospheric pressure is $P_0$. The cylinder is moved at an acceleration $a$ horizontally right. I need to find which base would have to ...
0
votes
2answers
51 views
Momentum, Impulse and Newton's Second Law of Motion
Newton formulated his Second Law as such:
$$\sum{\vec{F}} = \frac{\delta \vec{p}}{\delta t}$$
and of course, $\vec{p} = m \vec{v}$.
Why is it that if the net force $\sum \vec{F}$ is constant (which ...
5
votes
2answers
78 views
How can a car's engine move the car?
Newton's First Law of Motion states that an object at rest or uniform motion tends to stay in that state of motion unless an unbalanced, external force acts on it.
Say if I were in a car and I push ...
0
votes
1answer
226 views
Physics of Banked Curves at an angle [closed]
When calculating the normal force of an object on a ramp inclined at an angle,
the force of gravity is broken into components: $f_{gx}$ and $f_{gy}$, where $f_{gx} = f_g \sin (\theta)$ and $f_{gy} = ...
0
votes
2answers
355 views
From knowing just the change in kinetic energy, can we find the friction force and engine power?
I understand this topic well enough to get all the task done because they aren't very creative. But for my exam I think I should have this clear.
During the acceleration the force from the engine is ...
1
vote
1answer
113 views
Force and Torque Question on an isolated system
If there's a rigid rod in space, and you give some external force perpendicular to the rod at one of the ends for a short time, what happens?
Specifically:
What dependence does the moment of inertia ...
-1
votes
1answer
37 views
If An Object Explodes With A Force, What Force Are Fragments Given?
So let's say for example I have an object with 5kg of mass.
It explodes with a force of 500N.
The object fragments into four fragments: a 0.5kg, a 1kg, a 1.5kg and a 2kg object.
What force does ...
7
votes
4answers
2k views
What is the cause of the normal force?
I've been wondering, what causes the normal force to exist?
In class the teacher never actually explains it, he just says "It has to be there because something has to counter gravity." While I ...
0
votes
1answer
41 views
Another Inclined plane question
I did the FBD, and I found too many variables which are not eliminating...Moreover, I believe this question is based on kinetic and static friction. But, $\mu$ here is ambiguously defined...How Do I ...
-1
votes
1answer
53 views
Comparing Static Frictions
In this figure, which of the static frictional forces will be more?
My aim isn't to solve this particular problem but to learn how is static friction distributed . Since each of the rough-surfaces ...
0
votes
2answers
58 views
Massless string Paradox
If we introduce the notion of a massless string to denote the fact that net force on a massless string will always be $0$, since it is massless . How can these massless strings ever accelerate when ...
6
votes
1answer
630 views
How does placing objects in liquids affect the mass?
I was dazing off in my physics class when I came up with this question and I was wondering about it all day. I could not provide myself with an adequate solution, so here I am asking the forum about ...
0
votes
3answers
168 views
How do forces work
Is there a mechanistic-type explanation for how forces work? For example, two electrons repel each other. How does that happen? Other than saying that there are force fields that exert forces, how ...
1
vote
1answer
50 views
How large of a solar sail would be needed to travel to mars in under a year?
I'm attempting to approach this using the identity
$$F/A = I/c$$
I can solve for Area easily enough
$$A = F(c/I)$$
and I know the distance $d$ is
$$d=1/2(at^2)$$
But I'm having difficulty trying to ...
2
votes
1answer
32 views
Falling through the ground [duplicate]
I do not know much about physics but I know that according to Newtons third law of motion when we walk we are pushing the ground down but the ground is pushing us up. What force is making the ground ...
0
votes
1answer
204 views
What is the relation between fan blade and air flow CFM?
If I have a motor use in 2 cases, the 1st case I use standard blade and 20% longer blade in the 2nd case.
People told me that longer blade will create higher CFM. However, I am not totally sure. ...
4
votes
3answers
963 views
“Find the net force the southern hemisphere of a uniformly charged sphere exerts on the northern hemisphere”
This is Griffiths, Introduction to Electrodynamics, 2.43, if you have the book.
The problem states Find the net force that the southern hemisphere of a uniformly charged sphere exerts on the ...
-1
votes
1answer
47 views
A theoretical problem on Mechanics [closed]
Two particles with masses $m_1$ and $m_2$ are moving in 3D space with some Cartesian coordinate system. There are known the laws of motion of these particles, i.e. the position vectors $\vec{r_1}(t)$ ...
1
vote
1answer
48 views
Forces on a particle moving in a vertical circle
In the diagrma, a particle (A, mass 0.6kg) is moving in a vertical circle. The question is: When it gets to the lowest point, what is the tension in the light rod that is between the center of the ...
-2
votes
2answers
96 views
Repulsion does not exist; Gravity assist slingshot as a repulsive force [closed]
unification theory might say that there is only one force in universe that is called gravity(attraction).
So at atomic level for same charges that repel eachother(electrons etc.), if thought of as a ...
1
vote
4answers
2k views
Upward force on a object at rest
Is there an upward force on a object at rest? If yes, where does it come from?
3
votes
4answers
2k views
Calculating impact force for a falling object?
Good evening, I'm trying to calculate what kind of impact force a falling object would have once it hit something. This is my attempt so far:
Because $x= \frac{1}{2} at^2$, $t=\sqrt{2x/a}$
$v=at$, ...
4
votes
3answers
2k views
Why are bicycle pedal threads' handedness left on the left and right on the right?
I understand the reason that bicycle pedals are oppositely threaded on either side. What I don't understand is why it works because I'm missing something.
Take the right pedal for example. It's ...
0
votes
1answer
56 views
Why body starts moving when force is applied? [duplicate]
The recent question by m.buettner regarding self-inductance and its resistance to EMF Faraday's law - does the induced current's magnetic field affect the change in flux?, recalled me the ...
-1
votes
0answers
36 views
Does throwing a football harder/faster mean someone has more strength? [closed]
I have played football with another individual and noticed that they are able to propel this ball faster and harder than me, despite me being able to out lift them in virtually almost every major ...
1
vote
0answers
16 views
Acceleration by spherical particles (micron-scale) by an external force
I am looking for an expression for the velocity of a micron sized (1 - 10 micron diameter) sized particles under accelerating forces.
I have aerosols in mind.
This is what I have in mind
The ...
1
vote
0answers
49 views
Does the slinky base stay perfectly level during the initial free fall [duplicate]
In this related question:
Slinky base does not immediately fall due to gravity
It is observed that the base does not fall immediately.
Obviously the center of mass is in free fall, and the tension ...
0
votes
1answer
49 views
Measuring vibration and converting to force (N)
The test is:
To have a rotating machine, bolted into a factory floor.
To measure the vibration on 3 axis (output of accelerometers can be acceleration or velocity in $\mathrm{m/s}$ or ...
0
votes
1answer
90 views
Shear Flow corresponding to Eccentric Shear Force of a Closed-section Beam (Structural Analysis - Mechanics)
Been stumped with this question for way too long... its a beam with a thin-walled rectangular cross-section, and a shear force is acting at a distance from the shear center. I know my decomposition of ...
2
votes
1answer
50 views
Air pressure relative to a force on a bag?
Assume an airtight bag occupied by air such that the pressure inside the bag is equal to the atmospheric pressure. Assume the surface tension of the bag is negligible.
What is the change in air ...
1
vote
2answers
54 views
Clarification regarding Newton's Third Law of Motion and why movement is possible [duplicate]
Newton's third law states that to every action, there is an equal and opposite reaction.
If that's the case, then how do things move at all? Shouldn't all applied forces be canceled by the equal and ...
6
votes
2answers
586 views
Can a force in an explicitly time dependent classical system be conservative?
If I consider equations of motion derived from the pinciple of least action for an explicilty time dependend Lagrangian
$$\delta S[L[q(\text{t}),q'(\text{t}),{\bf t}]]=0,$$
under what ...
1
vote
1answer
70 views
Does the strong (nuclear) force ever contribute to decay?
Does the strong (nuclear) force ever contribute to decay ?
Or is the weak nuclear force the only decaying force ?
