All Questions
21,462 questions
29
votes
9
answers
2k
views
Effect of drag on projectile flight time - simple solution?
I saw a question like this in an AS-level physics paper (consisting of 40 questions given to ~17-year-olds, with a 75-minute time limit):
Two identical balls, x and y, are thrown up from the earth's ...
- 299
0
votes
2
answers
97
views
How to draw the Coriolis force in 2D?
I'm studying Geophysical fluid dynamics, especially the Coriolis force.
Now, in my book, this force$^{1}$ is defined as:
$$ \vec{F_c} = -fv \hat{x} + fu \hat{y} $$
where ($u,v$) are the components of ...
- 3
-1
votes
1
answer
113
views
Why doesn't Newton's Third Law prevent work from being done?
I apply a force on an object. The object applies an equal and opposite force on me. I realize the forces are on two distinct bodies and do not cancel each other out. Accordingly, the work done by me ...
- 202
0
votes
1
answer
25
views
Is it necessary that centre of gravity always coincident with geometrical Centroid for 4 point particle?
see the figure:
The cross quadrilateral (also known as a butterfly quadrilateral) has a centroid that appears outside when drawn using GeoGebra. However, when equal masses are placed at points A, B, ...
- 327
1
vote
0
answers
41
views
Possibility of rolling of a sphere up a very rough incline
Is it possible that a ball kept on a rough inclined plane rolls purely without slipping (immediately or after some time) ,when it is struck in a manner that it acquires only linear velocity along the ...
- 491
7
votes
5
answers
2k
views
Is speed conserved in bouncing from a rigid surface?
In this figure (p.21, fig.3.5)
a ball with velocity $v_i$ bounces elastically on a surface with an
incident angle $\theta$ with respect to the normal. Due to the
conservation of kinetic energy the ...
- 335
5
votes
1
answer
154
views
"Pressure" due to gravitational compression in a uniform sphere
I was trying to solve the following problem from the book Problems in General Physics by I.E. Irodov:
1.216: A uniform sphere has a mass M and radius R. Find the pressure p inside the sphere, caused ...
0
votes
1
answer
89
views
Animating the path of a moving object placed at the top of a circular surface and moving into free fall
I was trying to do an animation of an object sliding on a circular surface.
It starts at the top, moves to the right, loses contact, then proceeds to fall freely.
I want to know if there is a way to ...
- 101
0
votes
5
answers
104
views
Two people on ice floor
If person A is pushing person B, then A experiences a force coming from B by Newton's third law. This means that B is doing working on A. However, according to my intuition, A feels tired while B ...
-3
votes
1
answer
58
views
Deriving the Lagrangian In a general case
The title might lead to a different interpretation than what I what to ask. I will write what I have so far in the hope of solving this possible misunderstanding.
Assume that we have a function $\vec{...
- 770
0
votes
1
answer
48
views
Showing hinge constraint conserves system energy
Suppose we have two objects floating in space connected via an ideal hinge(IE frictionless).
Suppose they have initial conditions on their positions, orientations and current velocities.
How can it be ...
- 982
3
votes
1
answer
50
views
Understanding fictitious forces [closed]
My question is a little difficult to understand so I am using 2 images,
In the 1st image we can see that an block is kept at rest with respect to an inertial frame and we could say that net forces ...
- 33
2
votes
1
answer
194
views
Work-energy theorem for time-varying mass system
What I have studied in books is that "Work done by all the forces acting on a body is equal to the change in kinetic energy of the system" as the Work-Energy Theorem says.
But for the ...
2
votes
4
answers
144
views
Lagrangian - does it rely on Newtonian mechanics?
The thing that I can’t understand about Lagrangian mechanics is that to arrive at $T$ and $V$ you need to consider the work done, and that uses $\text{force}
\times \text{distance}$ which uses $f=ma$ ...
2
votes
1
answer
88
views
Fluid pressure and wall stiffness
I come from a medical background, but this is what I understand about the origin of fluid pressure. Please correct me, if I am wrong about this.
Fluids especially liquids, have pressure virtue of the ...
- 56
2
votes
1
answer
140
views
Does the angle between total acceleration and centripetal acceleration change in circular motion?
In a circular motion, if we have a particle moving with changing magnitude in velocity, does the angle between radial acceleration and total acceleration change?
0
votes
3
answers
68
views
Excursion in Chasles' theorem
The picture above is from
David Morin's book Introduction To Classical Mechanics page 371
I couldn't comprehend what he meant by motion like
Would I be able to find velocity of any point if I know ...
-3
votes
1
answer
87
views
Graphical relation between kinetic energy and mass
If we plot the graph of kinetic energy and mass through the formula KE = 1/2(mv^2), this would give a straight line but when we use KE = p^2/2m , where p is momentum, and then we plot the graph ...
-10
votes
1
answer
126
views
Has anyone tried to work gravity formulas based on energies instead of mass? [closed]
If Adam Reiss, 2011 Nobel Prize winner says negative mass must exist in our universe and published this in his Nobel winning paper, then why is mainstream science not on board?
He not only shows that ...
2
votes
1
answer
125
views
Possible errors in my textbook about Cavendish experiment?
We all know the Cavendish experiment and but my textbook "Concepts of Physics" by HC Verma on page 204 has given something extra which I dont get.
Let me write what it said
Let mass of ...
- 360
0
votes
1
answer
44
views
Stability of 2 objects in uniform motion due to friction
When two objects are in relative motion, be it in relative translational motion or one rolling on another surface, sliding friction converges them to uniform motion thereby eliminating relative motion....
- 85
1
vote
0
answers
15
views
Time-scale of energy transfer between vibration modes?
Consider N (roughly 3 to 10) particles interacting by Lennard-Jones potential having given total energy E and simulated in vacuum. Initially they form some cluster and they vibrate roughly at the ...
- 905
1
vote
1
answer
45
views
Does the speed of the roll become infinitely large near the end of this motion of the fire hose problem described below? [closed]
There is a problem about the rolling motion of a fire hose which is explained in the images below. Since the speed gets infinitely large at the end, there is a problem in the mathematical model used ...
- 19
0
votes
2
answers
63
views
Is the centripetal acceleration of a particle greater at the lowest point or at the highest point?
As shown in the figure above, the center D of the blue circle revolves around the red circle once, and the particle G also revolves around the blue circle once. The path of particle G is the following ...
- 2,165
0
votes
0
answers
78
views
The acceleration due to gravity - differential equation [duplicate]
The law of universal gravitation states:
$$\vec{F}=-\frac{GMm}{r^2}\hat{r}$$
where we have the familiar $m$ for the small mass and $M$ for the big mass, $r$ being the distance between the center of ...
1
vote
0
answers
69
views
Why does accelerating an object require more energy at higher speeds if velocity is relative? [duplicate]
Consider a 1 kg mass in the following two scenarios:
The mass accelerates from 0 m/s to 1 m/s.
The mass accelerates from 1 m/s to 2 m/s.
The kinetic energy required for (1) is $ \frac{1}{2} \times 1^...
- 11
-4
votes
1
answer
83
views
Newton's Third Law in space [closed]
Newton's Third Law states that forces occur in pairs of equal magnitude acting in opposite directions on opposing bodies. When we push against a wall, the wall pushes back with a force of equal ...
0
votes
0
answers
41
views
How do you solve Euler's Equation of Motion for time-varying Moments?
I'm trying to simulate a 3DOF inverted pendulum (See my other post for details). My inverted pendulum will have moments imparted onto it for short durations at a time from cold gas thrusters sitting ...
- 45
12
votes
2
answers
2k
views
What is that commentator talking about saying that "the static/kinetic coefficient model is actually pretty lousy"? Do we have any better ideas?
In his answer to the question Can the coefficient of static friction be less than that of kinetic friction? Chad Orzel says:
As an aside, the static/kinetic coefficient model is actually pretty lousy....
- 137
-2
votes
1
answer
46
views
Why isn't angular momentum conserved if I take torque about the point on a frictional surface? [closed]
Lets say I have a box which is moving on a rough horizontal surface. Now if I take a point $P$ on the surface then the net torque on the box would be zero about $P$ since the force of friction acts in ...
- 45
-1
votes
1
answer
73
views
How much force is needed to keep a 1000kg satellite at LEO in a geostationary position? [closed]
There are many advantages to keeping communication satellites at LEO, but in order to maintain communications 24/7, you either need a swarm of satellites or multiple ground stations.
Assuming it is ...
- 17
-1
votes
1
answer
66
views
How to handle collisions with coalesced balls? [closed]
Suppose there's a rail where balls can slide frictionless in a clockwise direction (positive speed) and counterclockwise direction (negative speed).
Computing the speeds after collision of ball B1 at -...
-3
votes
1
answer
44
views
Force calculation exercise [closed]
I'm a student working on a problem, and I'm struggling with part (d), which asks: 'What is the maximum angle?' I know the answer should be 40 degrees, but my solution gives 46.67. I'd really ...
0
votes
3
answers
120
views
Difference between effect of a force and an impulse
I came through a saying that
"A regular force (force acting on the body throughout the consideration) or torque corresponding to that force will produce an acceleration/angular acceleration ...
- 11
1
vote
3
answers
63
views
What force does a braking caravan exercise?
I'm not a physicist, and I hope this isn't a naive question!
Let's assume a car towing a caravan has powerful anti-lock brakes. Let's also assume the caravan has a braking system, as required in law, ...
1
vote
1
answer
89
views
Coriolis force question about the velocity vector decomposition
I am continuing this question to this one as a new one in order to not post to many questions under one title.
On the wiki page about Coriolis force there is a picture to help demonstrate the concept:
...
- 904
4
votes
2
answers
980
views
Normal force doing work, so conservation of energy not applicable but then getting wrong answer
Before coming to my actual question, let me write some assumptions that I believe we both agree on:
Normal force can do work (for example in an elevator)
Normal force is always perpendicular to the ...
- 360
0
votes
1
answer
50
views
Tension in chain/rope over wedge
Edit:
How is it possible to show that the tension in a rope passing over an edge/corner is constant?
There is a great variety of problems in engineering mechanics involving chains/ropes passing over ...
- 126
2
votes
1
answer
103
views
Coriolis force example confusion
I have a question about the Coriolis force
. On the wiki article, there is a carousel scenario described.
The figure illustrates a ball tossed from 12:00 o'clock toward the center of a counter-...
- 904
0
votes
1
answer
42
views
Does the Earth’s Geoelectric field affect its orbit around the Sun?
https://en.wikipedia.org/wiki/Atmospheric_electricity
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geoelectric-field
Is the interaction between the electric field of the Sun and ...
- 11
1
vote
0
answers
51
views
Verifying Hooke's law through video analysis in a dynamic setup
For educational purposes, I am attempting to experimentally verify Hooke's Law using a dynamic setup analyzed through video footage. In this experiment, a body of mass $m$ is accelerated by a spring. ...
- 1,820
3
votes
5
answers
138
views
Why is the potential of a pendulum $mgh$?
In all pendulum examples I've (assuming motion on the xy plane and no small angle approximation) textbooks say $\frac{1}{2} m (\dot{x}^2 + \dot{y}^2)+ m g y = constant$.
However, why is the potential ...
- 131
11
votes
8
answers
2k
views
What is the definition of Force?
I've come across so many abstract definitions of force—like "an interaction between two bodies" or "something that changes the state of motion or shape of a body." But what exactly ...
- 111
1
vote
1
answer
49
views
Accelerating body with decreasing mass [closed]
Hello,
This is a high-school level question so the answer is obviously B by using F = ma with a constant force and decreasing mass.
However, if one considers the decreasing mass and F = dp/dt, things ...
- 25
1
vote
6
answers
397
views
Static equivalence of forces and moment
Can someone please explain how the bottom two are equal, how does the bottom F result in a couple with the top left F.
Can't you just in that case say that the two upward forces on their own are also ...
- 11
0
votes
3
answers
164
views
What is the fastest possible speed of walking?
Consider a human with 2 thin legs each with mass $m$ and length $L$, and the rest of the body has mass $M$. I want to know what is the fastest speed it may walk, without leaving the ground.
If we ...
- 251
1
vote
3
answers
70
views
Do conservative force fields excert zero torque over rigid bodies? (The force acts on every part of the body)
I read Andrew H. answer in Torque produced by conservative forces vs Torque produced by non-conservative forces but couldn't understant why the last integral is zero. Answers justifying (or ...
- 13
2
votes
1
answer
107
views
Rotational motion of motorcycle on wall of death?
I assume you're familiar with the set-up of the 'wall of death'. (Basically, a motorcycle drives in circles in a horizontal plane on the inside curved surface of a non-smooth cylinder whose axis of ...
3
votes
2
answers
115
views
Role of Normal Force in Non-Uniform Vertical Circular Motion
Question
There are 2 instances of vertical non-circular motion that I don't quite understand.
Case 1
Description
In this situation, a marble of mass $m$ is moving on the inside of a vertical circular ...
- 33
0
votes
3
answers
85
views
What is the tension of a string with forces on both sides and how does it relates with net force?
If two objects A and B are pulling on different side of the string with forces respectively $F_1$ and $F_2$. Now, what will be the tension of the string in both of the following cases:
The string is ...
- 3