All Questions
Tagged with motion or kinematics
4,321 questions
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Speed is equal to distance divided by time but is this correct?
In this study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9784821/, the distance the punch travelled from start to impact is 0.49 meters and the time taken from start of punch (that's it, they define ...
- 364
0
votes
1
answer
39
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Extrapolating time to infinity for a particle moving spirally outward
If I have a particle moving radially away from me in a straight line and I extrapolate time to infinity, I could see the particle in a particular direction (given enough time for the light to reach me)...
- 1,254
-2
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2
answers
426
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How to Measure the depth of a Hole by Dropping a Rock? [closed]
Let's say I have a rock and a stopwatch.
I am standing on the edge of a deep hole or canyon, and can see the bottom.
How would I go about measuring the depth of the hole?
- 101
2
votes
2
answers
53
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Does coordinate acceleration match proper acceleration when $v=0, s=0$?
Alice and Bob are riding in their rocket at arbitrary proper acceleration through an arbitrary region of spacetime.
Bob steps out of the space ship right next to Alice, such that at $t=t'=0$, $v=0$, ...
- 14.1k
0
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2
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31
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Do these two refer to the same reference frame? [duplicate]
What exactly is the difference between a reference frame and a coordinate system (with respect to classical mechanics only)?
Can we claim that these two coordinate systems is from same reference frame?...
- 141
1
vote
0
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48
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Calculation of displacement field from a strain field
I am trying to calculate the displacement field from a given strain field in 3D. It is quite a cumbersome calculation, as presented in Applied mechanics of solids by Bower;
\begin{equation}
u_i(x) ...
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0
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5
answers
97
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Motion formula gives correct answer but without formula gives wrong answer [duplicate]
Assume a body with initial velocity= 10 ms final velocity= 20 ms and acceleration= 2 ms , so the time to reach final velocity will be 5 seconds. If we try to find distance it will travel in 5 seconds ...
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-1
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1
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113
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Can distance traveled by a body be zero?
I had seen a teacher saying on YouTube that we must note that distance traveled can not be zero then I searched for the same on net and surely some sources say same e.g. the below link
https://byjus....
- 1,395
2
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3
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112
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Why is it suitable to use $s= \frac{1}{2}at^2$ in this situation?
Question: A car slows down uniformly on a straight road, and come to rest in 3 m . What is the ratio of the time it takes to travel each of these three metres?
So this may be quite a simple question ...
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0
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1
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42
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Spinning mass around Spring with gravity
I've seen similar posts, but none in which a mass rotates vertically while connected to a spring, with gravity acting on the mass. I want to know if the path of the mass can be described with ...
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0
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7
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104
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How does the result of derivative become different from average ratio calculation?
Lets give an example. Velocity, $v=ds/dt$. If we know the value of $s$ (displacement) and $t$ (time), we can instantly find the value of $v$. But then this $v$ will be the average velocity.
Now ...
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0
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2
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53
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How to find the resultant speed component, and finding the angle in which the trajectory had hit the ground?
When having a trajectory traveling over a projectile, both the vertical and horizontal velocity components must be obtained in order to calculate the resultant velocity.
The question is: Why the ...
0
votes
1
answer
84
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How to Express the Cross Section of a Three-Body Final State Scattering in Terms of Invariant Masses $s_{ij}$?
I'm working on calculating the cross section for a scattering process that results in three bodies in the final state. My goal is to express the cross section in terms of the invariant masses $s_{ij}$...
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0
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2
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78
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Why can't we have accelaration in the form of meters per minutes*seconds?
I have been pondering over a concept regarding the general formula for acceleration, which is widely accepted as $\frac{m}{s^2}$. This formula elegantly illustrates that a given mass or body is ...
0
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1
answer
75
views
Does spinning the umbrella slow down the fall more?
Ignoring its structural weakness, if you jump from some height and use an umbrella to slow down the fall, would making it spin while you're falling affect the speed in any way?
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1
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1
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84
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Why centripetal acceleration does not causes the rotating particle to reduce the radius of its circular path?
I think that the centripetal force must develop a corresponding centripetal velocity that keeps on increasing as time passes because, $v = u + at$
Centripetal velocity constantly increases in terms of ...
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1
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1
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141
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What is the point/meaning of a trajectory equation
I have just learned about the trajectory equation and it is defined as such in my textbook
An equation that relates the position vector of displacement(but not distance) of a particle along x and y ...
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-1
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2
answers
80
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Problem with resources, Walter Lewin's third lecture
I've watched Walter's third lecture in 8.01 and I have a small problem with the last part, where he says that $$\vec r_t=x_t\cdot \hat x\ +\ y_t\cdot \hat y\ +\ z_t\cdot \hat z \\ \vec v_t=\frac{d\vec ...
1
vote
0
answers
57
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The correct dimensional formula for distance travelled in $n$th second? [closed]
I have read other similar questions on this site (including The dimensional formula of distance travelled in $n$th second with the same name), but it does not specifically answer what I was looking ...
2
votes
1
answer
60
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Velocity Needed For Water To Overcome Adhesion Force To A Rounded Steel Inclined Plane
Context: I work at a fast food restaurant with a 3-module sink. The sides are slightly angled down to allow the water to trickle down into the compartments. I found that water clings to the side of ...
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1
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0
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73
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Semi-Inclusive Deep Inelastic Scattering (SIDIS) kinematics
I'm having some trouble understanding the kinematics in SIDIS.
For example take the reaction $l+N\to l'+h+X$, where $l$ is a lepton, $N$ is the target Nucleon and $h$ is a hadron.
The kinematic ...
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-1
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1
answer
60
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Strain energy stored in a bungee cord pulled at its midpoint [closed]
A bungee cord that behaves elastically has an unstressed length $L=.76$ m and a stiffness $k=140$ N/m. The cord is attached to two pegs, distance $b=.38$ m apart, and pulled at its midpoint by a force ...
0
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0
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60
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Relation bitween Mandelstam Variables in three-body final state
What is the relation between Mandelstam variables in the three body final state?
There are 5 independent Mandelstam variables. What is the relationship between them?
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1
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1
answer
65
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What happens to $\frac{d}{dt}\left(\hat{v}\right)$ at the highest point a projectile reaches when launched vertically upwards?
Acceleration is given by $\dot{\vec{v}} = \frac{d}{dt}\left( v \hat{v}\right) = \dot{v} \hat{v} + v \dot{\hat{v}}$.
What happens to $\dot{\hat{v}}$ when the direction of velocity flips by $180^o$?
E....
0
votes
2
answers
225
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Why is the displacement -time graph of an object thrown upwards a downward parabola?
So, this is the displacement-time graph of an object thrown upwards with an initial velocity $u$. I understand the first part as the equation is $s = -ut + \frac{at^2}{2}$ which is simply the ...
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0
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2
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259
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Are there only 2 types of motion -- Translational & Rotational?
When searching up the different types of motion, results show circular motion, translational motion, oscillatory motion, rotational motion, periodic motion, etc. But just to clear things up in my head,...
1
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3
answers
101
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Are the concepts of motion such as mass, momentum, impulse, work, energy, force etc. fictitious/abstract concepts or are they real "things"?
I am a first-year undergrad studying maths and physics and whenever my professor introduces these concepts and the derivations of their associated laws i.e. conservation of momentum, work-energy ...
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1
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2
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94
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What is the locus of the velocity vectors of a boat navigating in the sea under the presence of some force?
I am a mathematician and know nothing about physics, although I am trying to solve a problem related to physics. If someone could help or provide some suggestions, I would be grateful.
I have a speedy ...
- 159
0
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2
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49
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Equations of motion for constant acceleration
I read that the equations of motion for a constant acceleration can be represented in a scalar form as well as a vector form, but what's the need to do them in vector form what extra can we do by ...
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1
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1
answer
152
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Lorentz-invariant phase space integral
Consider the following Lorentz invariant integral associated to a $2\to 2$ scattering:
\begin{equation*}
I = \int \frac{d^3\mathbf{p_3}}{(2\pi)^3 2E_3} \int \frac{d^3\mathbf{p_4}}{(2\pi)^3 2E_4} \...
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1
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1
answer
80
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How does relative motion work for an extended object?
I have this conceptual doubt which might be flawed very badly but I don't understand this particular thing. For example, if one end of a stick is moving with velocity $v_1$ and the other with $v_2$, ...
- 123
1
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2
answers
94
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Displacement and position vectors
I know that displacement vector means a change in the position vector of a body and also that change in displacement vector and change in position vector are not the same thing, but if we talk about a ...
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2
votes
1
answer
115
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Doubt regarding Velocity-Time graph with Constant Accleration [closed]
I think the answer is (A) initially. However, what about option (C)? It also shows a graph with constant acceleration and a negative slope. And in option (E), the acceleration is 0. Can we consider ...
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0
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4
answers
213
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Why acceleration is not always parallel to velocity but velocity is always parallel to displacement? [closed]
Velocity is derivative of displacement :
$$\vec v=\frac{\mathrm {d\vec r}}{\mathrm dt}$$
And acceleration is derivative of velocity.
$$\vec a=\frac{\mathrm {d\vec v}}{\mathrm dt}$$
Given that their ...
- 325
1
vote
2
answers
52
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Setting $u$ = escape velocity when calculating the maximum height of a thrown object
So, if I throw an object at some velocity $v$ at an angle θ, the maximum height reached by the object is $\frac{v^2\sin^2{\theta}}{2g}$ but, I know this isnt true. clearly in a weird way, the height ...
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0
votes
3
answers
169
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Why does the equation of a wave contain the term $\omega t$ instead of $vt$ in the wave equation $y=A\sin (kx-\omega t)$?
Why does the equation of a wave contain the term $\omega t$ instead of $vt$ in the wave equation
$$y=A\sin (kx-\omega t).$$
I think of the constant $k$ which for higher values increases the frequency $...
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0
votes
0
answers
24
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Energy in projectile motion
When approaching a projectile motion problem using the conservation of mechanical energy, why do we use the speed of the object as a whole and not only the vertical component?
The horizontal motion of ...
0
votes
2
answers
80
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Vectors in inertial and non-inertial frames
Trying to understand how vectors change in inertial and non-inertial frames
Am I right in saying vectors are defined by their invariance under coordinate transformations? My main question is are ...
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0
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2
answers
84
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Solving a PDE using $x-vt$ as a variable
So I was reading this Landau and Lifshitz paper:
https://doi.org/10.1016/B978-0-08-036364-6.50008-9
The article can also be found without a paywall by just searching its title, "On the Theory of ...
9
votes
2
answers
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Which way does a stone move when hit by a wheel/tire?
I don't think this exact question has been asked before in the physics section. I am mostly interested in understanding it conceptually rather than calculation. I have asked the same question in the ...
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1
answer
88
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Why don't they use golf ball dimples on bullets or cannon balls? [duplicate]
Dimples help the golf ball to fly far. But do you know why they don't use them on bullets or cannon balls?
Some kinds of cannon ball have similar size as a golf ball.
1
vote
0
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138
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In gyroscopic effect of a quadcopter, why does precession cause torque, not vice versa?
I don't know if the header corresponds to my actual quest but i will explain.
In quadcopter dynamic equations of Newton-Euler formation that I have encountered in all academic publications, torque ...
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-1
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1
answer
44
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Components of velocity in projectile motion [closed]
I came across this question in my physics textbook (Gr12) and I was hoping someone could explain the solution to me
A ball is thrown horizontally off a building at $8.2\,\text{m}/\text{s}$. At a ...
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0
votes
1
answer
95
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Is it possible to have a uniform speed but variable velocity in one-dimension motion?
Is it possible to have a uniform speed but variable velocity in one-dimension motion? I saw a lecture where teacher said that it is possible if particle changes its direction of motion 180$^\circ$.
...
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1
vote
1
answer
71
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High school kinematics problem [closed]
From a town, cars start at regular intervals of 30 seconds and run towards, another town with a constant speed of 60km/h. At some point of time, all the cars simultaneously have to reduce their speeds ...
0
votes
1
answer
57
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Argument for distance in terms of acceleration [duplicate]
This, I know might perfectly be a very stupid question. But trying to make sense of it in terms of a very simple explanation. For distance $d=vt$. Velocity might be another function of time $v=at$. ...
0
votes
4
answers
77
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Percentage change in K.E for a given change in momentum
I couldn't get through this 'easy question' that was in my morning exam, it goes
Q. If linear momentum of body is increased by 50%, then K.E of that body increases by....%
**My solution **
K.E = $E=\...
- 387
0
votes
1
answer
89
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In $a = dv/dt$, is $a$ the net acceleration? [closed]
While going through the calculus approach to accelerate, we have,
$$a = dv/dt, $$
I think, here, v and a should be in the same axis,
is my process correct?
in a planar motion in two dimensions, it ...
- 1
0
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2
answers
89
views
How to calculate the final position of a particle under variable accelaration and its instantenous velocity?
I'm a first-semester physics student who was recently on a train. On a screen, it said the instantaneous velocity of the train was 176 km / h. We had 4 min left until our destination. I wanted to ...
- 127
1
vote
2
answers
142
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Average velocity showing different results
I was solving a question, in which, a particle has travelled a distance $s$, with initial velocity $0$ and constant acceleration.
So the equation of motion becomes,
$$ v = a t \tag{1} $$
and
$$ v = \...
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