All Questions
Tagged with motion or kinematics
4,321 questions
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Mandelstam variables
For a while now I have been struggling with a problem I am facing when considering the 2 to 2 process (Mandestam variables), and I would like to have an understanding of what is going on.
Considering ...
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What can we say about the dependence of resistive force on the velocity v of the bead? [closed]
Consider a fixed vertical circle. A large number of smooth, thin rods are fixed along the chords of the circle, all at different angles to the vertical. All the rods have their upper end at the ...
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Question on minimum distance between two projectiles, considering drag force [closed]
The following was a question posed in a recent test series:
What would the intended solution be to such a question? Are there any defining features that could be used to simplify the problem or is ...
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3
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What does the derivative of unit vector of velocity with respect to time represent?
let an object move with a constant accelration a. in my book,the following derivatve is said to be non-constant(variable).
$$\frac{d[\frac{v}{|v|}]}{dt}$$
what does this mean?
as far as i can think,it ...
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Gravitational field of a moving object
Here's a simple scenario:
Let's say, that there are 2 stationary planetoids of equal mass on the Earth's orbital motion path, placed at equal distances from Earth just like on the image below:
Will ...
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310
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18
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Why does kinetic energy increase quadratically, not linearly, with speed?
As Wikipedia says:
[...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$.
Why does this not increase linearly with speed? Why does it take so ...
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Vertical motion of an object under air drag and gravity [closed]
The air drag exerted on an object is proportional to its speed. Toss the object with initial speed $v_1$ upwards from the ground. If its landing speed is $v_2$, find the time of motion.
My solution.
...
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3
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Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field
When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
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2
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Difference in answer using relative motion and that without (Newtonian Mechanics)
The question:
Two bodies move in a straight line towards each other at initial velocities $v_1$ and $v_2$ and with constant accelerations $a_1$ and $a_2$ directed against the corresponding ...
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4
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How can I detect when a car makes a turn using velocity vectors and account for speed?
I am trying to detect when a car makes a turn by analyzing its velocity vectors over time. Each velocity vector is represented as:
$$\vec{v_t} = (X_v, Y_v)$$
Currently, I calculate the change in ...
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1
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Need help in understanding Tangential Acceleration [closed]
I am studying Circular motion and I am confused about tangential acceleration and tangential velocity. I am studying uniform circular motion and it says the tangential acceleration is $0$ in uniform ...
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Kinetic friction with no force on an object
We've learnt that friction is the opposition of motion and that friction appears the instant a force is applied on an object i.e when an object is at rest (with no force acting on it) then there is no ...
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3
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Question about the the velocity and acceleration in tensor notation
When computing the volicty of a particle moving along a curve parametrized by $Z^i(t)$ for each component i, the components of the velocity $V^i$ are given by $$V^i = (d/dt)Z^i$$ and the components fo ...
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Minimizing travel time of a car given some confusing constraints
I came across a fairly basic kinematics question in the first chapter of "An Introduction to Mechanics, 2nd Edition" by Kleppner & Kolenkow:
"A sportscar, Electro-Fiasco I, can ...
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5
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865
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Is there an agreed upon physics definition of the term 'speed'? For example, can it be negative?
The term speed is commonly defined as follows:
https://www.physicsclassroom.com/class/1DKin/Lesson-1/Scalars-and-Vectors
Speed, being a scalar quantity, is the rate at which an object covers ...
- 213k
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153
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Why is $v^2= u^2-2as$ if acceleration is negative?
Why is $v^2= u^2-2as$ if acceleration is negative? Wouldn't that bring the acceleration in the answer as positive?
Suppose $v=0, \ u=90 \ \text{m/s}$, $s = 0.6 \ \text{m}$. Then, using $v^2-u^2 = -2as$...
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How is the $v^2-u^2 = 2as$ modified as $v^2-u^2 = -2as$ [duplicate]
I don't understand how, when an object is retarding, its equation of motion $v^2-u^2 = 2as$ becomes $v^2-u^2 = -2as.$
- 61.8k
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Acceleration-distance graphs
I solved the above quite theoretically, differentiating with respect to time the equation of the given graph $$v=mx+v_0,$$ where $m=\frac{-v_0}{x_0}$ is negative and $v_0$ is positive. Thus, $$a=m^2x+...
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How to find 4-acceleration scalar product in terms of $ds$ spacetime interval?
We know 4-velocity $$U^i =dx^i/ds$$ where $$ds=\sqrt{dx^idx_i}$$ so we have 4-acceleration $$A^i=dU^i/ds$$
Then we have $$A^iA_i=\dfrac{dU^i}{ds}\dfrac{dU_i}{ds}$$
How should I proceed to find this ...
- 3,265
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5
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280
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Why doesn’t a cart accelerate when I push it with a constant force?
If I push a cart with a constant force, it moves at a constant velocity, so there must be no net force. The applied force must be canceled out by kinetic friction and air resistance, but the magnitude ...
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Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant but acceleration is constant?
Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant, but rate of change of velocity is constant?
Like speed is only the magnitude, so ...
- 213k
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2
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364
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Calculate launch angle of object moving away from view
I'm writing image processing software and my goal here is to take an image of a projectile moving away from the camera and determine the launch angle. What I already know is:
The actual size of the ...
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3
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Projectile, air resistance and wind
So for my school project I am working on a projectile simulator and air resistance.
So I have looked at this.
Equations for an object moving linearly but with air resistance taken into account?
...
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863
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Kinetic energy produced in an explosion
If there is a train moving at 2 m/s with a cannon attached to it loaded with a ball, and then the ball is launched from the train, how would one find the kinetic energy produced by the explosion if ...
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Equilibrium partitioning between two domains with different mobility
Imagine a random walk in a system consisting of two adjacent phases. In one of the phases the walker has a high mobility, and in the other low mobility.
If I'm not mistaken, the walker will in this ...
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70
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Use of $dv/ds$ in defining acceleration [duplicate]
We can write acceleration as either
$dv/dt$ or $v dv/ds$.
And surprisingly the work-energy theorem arrives from the second definition.
I feel it would be fundamentally understanding towards work ...
- 213k
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1
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Simplification of the Differential Cross Section in Peskin and Schroeder
I am reading p. 107 in Peskin and Schroeder's QFT, and I am stucked on one of the steps they took while calculation $2\rightarrow 2$ cross section. For $A+B\rightarrow 1+2$ differential cross section ...
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606
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How to determine the minimum "Arrival Distance" given a maximum velocity, acceleration and jerk along with an initial velocity and acceleration?
Problem
Given the following:
$A$ - maximum acceleration.
$J$ - constant jerk (the rate of change of acceleration).
$v$ - initial velocity.
$a$ - initial acceleration (where, in practice, $a ∈ [-A, A]$...
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Best way to calculate velocity, acceleration and jerk with different temporal resolutions
I have body motion tracking data I am using for my thesis. I am trying to find relationships between the kinematics of the body of speakers, and the acoustic measures of their speech (e.g. speech ...
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263
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How would one compute the path of an particle's motion from forces defined in different frames of reference?
I'm trying to write a computer program to render and play-back the path of a particle existing in 2D space given all forces acting on said particle. This is relatively easy to do if all forces are ...
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Can something be at rest if it has a non-zero acceleration?
I think I have a decent grasp on the physics - I understand that something can be accelerating while stationary. That's the basis of my question. I just wanted to clarify some of the language used.
We ...
- 41k
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327
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Need help interpreting displacement-time graphs
In this image is a displacement-time graph of the movement of an object. In the video (Khan Academy), the explanation is that between $0\,\text{s}$ and $5\,\text{s}$, the displacement of the object is ...
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Minimum energy of projectile to trigger a nuclear reaction and energy of ejectiles
I am studying the following type of nuclear reactions:
$$\text{projectile + target} \to \text{ejectile 1 + ejectile 2}.$$
I make the assumption that the target is static. This reaction needs energy to ...
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Acceleration-time graph to travel 1 meter in 1 second and eventually reach 0 velocity and 0 acceleration
How do I go about getting an equation of acceleration in terms of time such that an object travels $1$ meter in $1$ second, given that:
At $t = 0.5$, the acceleration is $0$ and the velocity is ...
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1
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Particle momentum in collision expressing in Mandelstam variable
Consider the $s$-channel process. I use the metric convection $(+,-,-,-)$. The constraints are: Conservation of four momentum: $p_{1}^{\mu}+p_{2}^{\mu}=p^{\mu}$ and on mass shell condition $p_{i}^{2}=...
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Shape of Trace of Chalk on a Blackboard (Kinematics problem) [closed]
A white piece of chalk is thrown onto a black horizontal board moving at constant velocity. Initially, the chalk's velocity was perpendicular to the board's direction of motion. What is the shape of ...
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Prove that relative velocity, momentum, and energy, are related by $E_1E_2v_{rel}=\sqrt{(p_1p_2)^2-m_1^2m_2^2}$
In Chapter 8 of F.Mandl's book Quantum Field Theory, during the derivation of the differential cross-section, the following relation is used:
$$E_1E_2v_{rel}=\sqrt{(p_1p_2)^2-m_1^2m_2^2} \,\, ,$$
...
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Uniform Circular Motion w/ Tension and Friction
So I had a problem today which I couldn't make any sense of. I don't have access to it at the moment but this is a pretty accurate approximation.
Basically, a mass (m) is swinging horizontally on ...
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Non-uniform deceleration model
I encounterd a brake model for an ERTMS system (E=Europe) with the following characteristics.
A point starts a decelerating proces at $t=0$ when $v=c$ but first there is a reaction time $T$ during ...
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355
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Direction of displacement
Displacement is defined as the vector obtained by joining the final position to the initial position (head towards the final position). Well,i know this is silly but what are these final and initial ...
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Why does a graph of radius vs velocity of an object undergoing circular motion have a quadratic slope? [closed]
I'm doing a project with uniform circular motion and I cannot for the life of me understand the conceptual side of the graphs. On a graph of velocity vs radius of a bob undergoing uniform circular ...
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Dark matter thermally averaged cross section
I'm trying to rederive the results of this classic paper:
https://doi.org/10.1016/0550-3213(91)90438-4
to find the thermally averaged cross-section. I am struggling with a change of variables and ...
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3
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Explaining the equations of motion in kinematics [closed]
Hi I Have these equations and I don't know and understand what each of them means.
Can someone help me?
$$\tag 1 v=v_0+at$$
$$\tag 2 x=v_0t+\frac{at^{2}}{2}$$
$$\tag 3 v^{2}=v_0^{2}+2ax$$
What does ...
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Inertia in a different medium than air or vacuum
I have a problem understanding inertia in a medium more viscose than vacuum or air.
Let's consider the classical bus experiment.
The bus (a closed system) is accelerated or decelerated and a person ...
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2
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88
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Problem with logic regarding projectile motion problems when only Range and Angle are given
Im struggling with understanding a problem with my logic in regards to solving problems relating to finding out an initial velocity when given a range $d$ and angle of elevation $\theta$. The main ...
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65
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In the kinematic equations, how is that possible while deriving an equation? [closed]
We have this kinematic equation:
$$x_f = x_i + v_it + \frac{1}{2} at^2.$$
Now, I do not have any problem with this equation, but where I have a problem with is the way we derived this equation.
We ...
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Why is the tangent of the rear wheel path of a bicycle parallel to the frame?
In "bicycle problems" (made famous for example by the book "Which Way Did the Bicycle Go?") the relevant point is the following: If $r(t)$ and $f(t)$ are the points of contact of ...
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Does pressure in a closed container increase or decrease with increase in acceleration of the container?
Let there be some air contained in a vessel whose walls are elastic. The vessel is closed and we impart some velocity to it. Please note that the gas inside the container is stationary w.r.t. the ...
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21
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What happens when a car starts moving? The last moment the car is at rest versus the first moment the car moves
Imagine a car that's at rest and then it starts moving. Consider these two moments:
The last moment the car is at rest.
The first moment the car moves.
The question is: what happens between these 2 ...
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Different Directions in a general curvilinear motion in a plane (Polar Coordinates)
In a polar coordinate system, We define 4 directions:
Radial Direction: Joining the origin with particle's position (represented by r)
Normal Direction: Perpendicular to the curve at a point (...
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