The description of the movement of bodies by their position, velocity, acceleration (and possibly higher time derivatives, such as, jerk) without concern for the underlying dynamics/forces/causes.

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3answers
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Negative vectors (e.g. velocity)

If you said someone had a velocity of $-12\,{\rm mph}$ and they were traveling north? Wouldn't it mean that they were traveling $12\,{\rm mph}$ south? This is a quote from here: if something [...
25
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5answers
6k views

How does a mobile phone vibrate without any external force?

How does a mobile phone vibrate without any external force? By Newton's law, any body can't move without any external force
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3answers
6k views

What is displacement? Position relative to a reference point or change of position

What is the "official" or most useful definition of displacement in the context of kinematics? There are two common ones: Displacement is the length and direction of a line from a fixed reference ...
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votes
1answer
51 views

Can velocity be negative? [closed]

In free fall I use the formula V=g*t and g is negative(-9.8m/s^2). It gives me negative.
0
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1answer
44 views

Derivation of centripetal acceleration

While reading HC Verma chapter 7 circular motion I came across a derivation which I couldnt understand. I have marked my doubt with red. I don't understand from where +dw/dt [- i sine +j cos0] came ...
0
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1answer
57 views

If two cars have the same acceleration at time $t$, are the velocities of the cars the same at time $t$?

So when I look at the question logically, I reason that if I had two cars: Range Rover and BMW, at time t, I could pump the gas and make them accelerate at the same rate at 0.5 m/s^2 but I could be ...
3
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2answers
93 views

Watching Airplanes Fly Toward You

Recently, I was enjoying the stars on a cool summer night and saw an airplane flying toward me from the distance. I observed its path as it started out as a small dot in the distance until it flew ...
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0answers
21 views

Two particles of different velocities travel through a region of time-dependant acceleration. At what time do they meet afterwards? [closed]

Two projectiles: $P_{1}$ and $P_{2}$ have velocities $v_{1}$ and $v_{2}$, both propagting in the x direction and starting at $x=0$. They propagate with constant velocity over a distance $L$ and reach ...
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2answers
55 views

Calculating acceleration via differentiation of velocity [closed]

I am just starting with calculus and kinematics. I saw this particular question: The velocity of a particle at a distance $x$ is given by $v^2 = 4\cdot (x \sin (x) + \cos (x))$. Find the ...
0
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0answers
22 views

kinematic constraint of spacecraft

I am now reading a paper about trying to use convex optimization to solve the attitude control of spacecraft. However, I do not have background on the physical part: Let 1. $\omega(t) = [\omega_1(...
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1answer
39 views

Calculating relative velocity in three dimensional space

Given two points $\mathcal{A}$ and $\mathcal{B}$ in $\mathbb{R^3}$ whose position and velocity vectors are, respectively: $$\mathbf{r_A}=\begin{pmatrix}r_{A_{x}}\\r_{A_{y}}\\r_{A_{z}}\end{pmatrix}$$ $$...
-3
votes
2answers
78 views

Use equations to create a realistic problem [closed]

Given the following equations: $100$ m = $0$ m + ($50 \cos\theta$ m/s)$t_1$ $0$ m = $0$ m + ($50 \sin\theta$ m/s)$t_1$ - $\frac{1}{2}(9.80$ m/s2$) t_1^2$ I am supposed to make up/create a real-life ...
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5answers
105 views

How can I find initial and final velocity? [closed]

Is there a way to find initial and final velocity if I only know the acceleration and distance and which formula must I use? I do not know the time either. EDIT Thank you for all your answers! You ...
3
votes
3answers
8k views

Finding the max height of a ball launched as a projectile using work-energy

A ball is launched as a projectile with initial speed $v$ at an angle $\theta$ above the horizontal. Using conservation of energy, find the maximum height $h_\text{max}$ of the ball's flight. Express ...
0
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2answers
77 views

Finding acceleration due to gravity of a 2D projectile

Can I find acceleration due to gravity of a 2D projectile given only the peak of the projectile, the point of impact, initial angle, and initial velocity? Specifically what is missing is the initial ...
0
votes
2answers
76 views

Average acceleration: why I am getting different results?

Let's consider a simple school problem. A car starts moving during 3 seconds with a constant acceleration of 1 m/s^2. Then it stops accelerating and moves 3 seconds more with a constant speed. Find ...
-1
votes
1answer
49 views

Time traveled assuming instant acceleration/decelaration

I am working on sort of a motion planning algorithm where I need to estimate the time it takes to travel along a certain path of points (straight lines between consecutive points, i.e I am assuming ...
3
votes
2answers
75 views

Best way of calculating average acceleration in lab experiments

I am doing a lab experiment that works as follows. An object moves along the $x$ axis with an initial acceleration and then moves with a pretty constant velocity that may slightly vary within $20\%$ (...
0
votes
1answer
54 views

Would displacement vs time of circular motion be a sin/cos curve or parabola

If you were to graph the displacement from one specific point in a circle of an object rotating, example the boomerangs displacement from the thrower. Would you use a parabola, since in a cos/sin ...
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0answers
38 views

When this CD is spun so fast that it shatters, why does the warped shape move slower than the surface?

In this video where a CD is spun abnormally fast to the point of shattering, one notices from the writing on the CD that the surface is spinning faster than the warp "shape" is. In other words, the ...
1
vote
1answer
41 views

Intuitive picture for Mandelstam $t$

In tree-level electron-positron scattering one has two possible channels corresponding to Mandelstam variables $s$ and $t$. The $s$-channel ist fine, there $\sqrt s$ is just the center of mass energy ...
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0answers
20 views

Particle interaction kinematics in lab frame

Attempting a question from a past paper on scattering kinematics, fixed particle mass $m$ is struck by another particle mass $m$ with kinetic energy $T$. By evaluating $s$, $t$ and $u$, and their sum ...
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2answers
78 views

Doubt on series springs [closed]

Here is a description of the motion of two springs in series. The premise is that the force on the two springs is the same. This is derived from the following reasoning: when I pull the mass with a ...
1
vote
2answers
103 views

I don't understand the formula of constant deceleration required to prevent a vehicle collision

As I was looking for the formula that an Intelligent Speed Assist technology use to calculate the required deceleration that a vehicle must apply avoid collision, I found this one: $$a = \frac{V^2_0 ...
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votes
3answers
1k views

Speed of an object in air versus in vacuum

Okay, imagine that you are shooting a rocket down a tunnel that is 60 miles long and the rocket is travelling at 60mph, so the rocket should reach the end of the tunnel in a hour, right? Yep, in an ...
0
votes
1answer
135 views

Find constant acceleration needed to reach point (possibly related to projectile motion on slopes) [closed]

Given a particle with a position $p_0$ and an initial velocity $\vec{v_0}$, what acceleration $\vec{a}$ do we need to reach point $p_1$ and how long until we have reached $p_1$? The magnitude of the ...
1
vote
1answer
61 views

Why does everything written on a page appear in concentric circles when we rotate that page? [closed]

When i put a pencil in the middle of a paper and rotate it very fast, whatsoever is written on it, will appear in concentric circles. What is the reason behind this phenomenon and what is it called?
8
votes
5answers
17k views

Why does work equal force times distance?

My 'government-issued' book literally says: Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
4
votes
3answers
218 views

Is $\dfrac{dx}{dt}$ a fraction or not?

I am new to calculus and during my mathematics class my sir defined $\dfrac{dx}{dt}$ as $$dx/dt=\lim_{t\to t_1}\dfrac{f(t)-f(t_1)}{t-t_1}$$ and my sir made a clear statement that $\dfrac{dx}{dt}$ ...
0
votes
1answer
53 views

Vector Derivative: General Case

From "An Introduction to Mechanics" by Kleppner & Kolenkow, SIE-2007, Chapter 1 (Vectors and Kinematics), Section 1.8 - "More about the derivative of a vector". In this section, towards the ...
2
votes
3answers
8k views

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?
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2answers
1k views

What is the highest energy position for a double pendulum? And for which energy positions is it chaotic?

Math/physics teachers love to break out the double pendulum as an example of chaotic motion that is very sensitive to initial conditions. I have some questions about specific properties: For a ...
0
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1answer
22 views

Does object traversing in linear motion have a constant bearing rate?

If an observer is moving at a constant rate and constant direction and another object traverses in front of the observer and is also moving in a fixed direction at a constant rate, will the bearing ...
0
votes
0answers
17 views

Kinetic gas theory: How large are rotational and vibrational energy for a linear diatomic molecule?

Let's say one has given a temperature of a simple linear diatomic gas like Hydrogen $H_2$. From the temperature one knows the energy of the gas, but how does this energy "split up" to the different ...
5
votes
1answer
133 views

Obtaining the temperature from Bose-Einstein and Fermi-Dirac distribution

Lets say you are given a distribution function $f(p)$ and you want to define a temperature, $T_f$, for this distribution. (I assume $\mu = 0$.) It is then natural to define a temperature the ...
0
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1answer
30 views

From a displacement-time table/graph, can one tell whether acceleration or jerk is constant?

Does constant acceleration equal a parabolic graph similar to $y=x^2$, while jerk follows the path of $y=x^3$? I was just thinking about this possibility. We are always told in physics class that ...
0
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0answers
21 views

Magnitude of Drag force correction on a bean bag

I am currently designing a ballistic launcher for an engineering project. Our task is to propel a bean bag approximately one hundred grams in mass ten feet with the lowest standard deviation possible. ...
0
votes
2answers
79 views

Is the motion of a particle non-analytic?

I really can't understand what happens during the time $t(0)$ to $t(0+dt)$ in the following crackpot arguement: A particle is at rest (in an ideal frictionless world) until $t(0)$. So every order ...
0
votes
1answer
41 views

Calculating the Velocity of an object far far away

I saw a satellite the other day, it moved very fast through the night sky. Now I know it took around 110 seconds for it to fully travel out of the night sky(out of my visual bounds assuming, that I'...
0
votes
2answers
33 views

If a block moves on a straight line (no friction) for time $T$ and then along an incline plane, what will the displacement vs. time graph look like?

In my opinion, the graph for the first part of the motion will be a straight line passing thorugh the origin (at the beiginning of motion) and then it will be a falling parabolic curve ( $x$ is ...
0
votes
0answers
20 views

Water Jet scenario [duplicate]

So I have a question I came across that goes along the lines of Water is discharged from a 20 mm diameter nozzle to the atmosphere. The water jet leaves the nozzle with a velocity of 12 m/s and is ...
4
votes
1answer
473 views

Lorentz-invariant phase space of a three-body decay process

I am not following the use of delta function in the 3-body decay process. In $\gamma^* \to gq\bar{q}$ process, with $\gamma^*$ being a virtual photon, we have a phase space factor $$d^9R_3 = \frac{d^...
0
votes
2answers
489 views

Tangential acceleration in circular motion?

A lot of my problems have objects moving in circular paths with tangential and normal components of acceleration. If the tangential component is non-zero though, the speed is changing so the radius ...
0
votes
2answers
53 views

How to find tangential and normal unit vector to a trajectory from the equation? [duplicate]

Considering a 2D motion in a plane and the equation of the trajectory of a point $y=f(x)$, I don't understand how exactly $\frac{\mathrm{d}y}{\mathrm{d}x}$ can be used. In particular if I'm looking ...
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vote
1answer
9k views

Calculation of Distance from measured Acceleration vs Time

I have an Accelerometer connected to a device that feeds the instant values of the acceleration in the 3 directions. I've tried to calculate the distance for a vertical movement using these values ...
8
votes
5answers
41k views

How to get distance when acceleration is not constant?

I have a background in calculus but don't really know anything about physics. Forgive me if this is a really basic question. The equation for distance of an accelerating object with constant ...
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vote
3answers
77 views

Moment of inertia of 4 particle system

Four particles are connected by rigid rods of negligible mass. The origin is at the center of the rectangle. The system rotates in the $xy$ plane about the z axis with an angular speed of $6$ rad/s. ...
8
votes
3answers
6k views

Radius of curvature

I have come across a question that asked me to find the radius of curvature of a projectile. As far as I know, the path of a projectile is a parabola and I have found mention of the radius of ...
1
vote
1answer
42 views

Conflicting answers gained from different equations

First time posting I hope this is the place. if someone could help me sort out formatting for the equations that would be nice "As a result of being hit from behind by a toy truck, a 50g toy car ...
1
vote
2answers
56 views

Simple dynamics problem

I was trying to solve a simple problem where it was given that the velocity of a box on a smooth surface is: $$ v = 0.05s^{3/2} $$ Where s is the number of meters that the box travels from rest. ...