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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56 views

Physical pendulum dynamics confusion

I'm validating a Matlab Simulink SimMechanics model analytically. The model consists of a physical pendulum (uniform rod with length $l$ and width $w$) which is torque driven. I'm somewhat confused ...
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2answers
438 views

Correct terminology for combined kinematic and dynamic state

The kinematic state is defined as the position and orientation in space. The dynamic state is defined as the associated velocities. What is the correct terminology for the combined kinematic and ...
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2answers
512 views

Horizontal and vertical acceleration of a ball on a slope?

I understand that you resolve the components of the balls weight parallel and perpendicular to the slope in order to calculate the force due to gravity that actually acts down the slope. The ...
-2
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1answer
44 views

How would you go about solving this tricky distance problem? [closed]

I've tried calculating the distance the runner has left to get to the finish line by the time the bird gets there and adding it to the distance the bird has to fly back to the runner. Then I ...
1
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2answers
977 views

Motion of a rod struck at one end

Imagine a strong metal rod of uniform density and thickness floating in a weightless environment. Imagine it lies on an X-Y plane, with one end (A) lying at 0,0, and the other end (B) at 0,1. Then it ...
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1answer
299 views

Kinematics of a differential drive robot

(I am reposting here a question I asked on stack overflow, since it actually sits right in between programming (modeling of 2D physics) and physics proper (kinematics). I think I have the physics part ...
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2answers
200 views

Kinematics equations of motion find x position in 2D from height

I have a question and I thought of 2 possible ways to answer it however the resulting answers are different which means I must be doing something wrong in my calculations. All the below happens 2 ...
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1answer
5k views

What factors affect the velocity of an object moving down an inclined plane?

If you have a small toy car rolling down an wooden plank, what factors would increase or decrease the velocity of said car. In the experiment my team originally stated that adding mass to the car ...
-1
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1answer
66 views

Considering velocity-distance graph [closed]

A car is travelling at constant velocity. Its brakes are then applied, causing uniform deceleration. Which graph shows the variation with distance s of the velocity v of the car? The solution is A, ...
3
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2answers
372 views

Projectile motion maximum distance to origin

Is there an elegant or easy way to derive the maximum distance from the origin to a point of the parabola created by projectile motion (assume initial position is the origin)? Other than ...
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2answers
986 views

Small Animal Terminal Velocity

I recently saw a cat fall probably 100 feet like in this video Cat Falls. It seemed as if the cat reached terminal velocity by the time it hit. Does this mean that cats (and other small animals) could ...
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2answers
86 views

Components of Velocity in polar co-ordinates

Consider a point moving along a curve in a plane. The position of a point P on a coordinate system can be specified by a single vector $\vec{r}$=$r\hat{r}$. A rough sketch describing the situation is ...
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2answers
46 views

How to calculate initial acceleration of a projectile motion? [closed]

I have an object following a projectile motion, that hasn't got horizontal acceleration but only vertical -g. What is the acceleration that I have to use in the second law of motion (F = ma) in order ...
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2answers
48 views

Finding the height of a balloon [closed]

A balloon moves up vertically such that if a stone is thrown from it with horizontal velocity $u$ relative to it, the stone always hits the ground at a fixed point $ 2u^2/g$ horizontally away from it. ...
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2answers
55 views

Is distance considered only for objects which have already moved?

I have this confusion concerning distance and speed. Typically, we express displacement and distance relative to a reference point, which we regard to be an unmoving location. As displacement has a ...
43
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12answers
83k views

What is the difference between “kinematics” and “dynamics”?

I have noticed that authors in the literature sometimes divide characteristics of some phenomenon into "kinematics" and "dynamics". I first encountered this in Jackson's E&M book, where, in ...
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2answers
46 views

How exactly do objects move

Suppose I have a piece of steel that is made up of one row of 100 atoms. Now, suppose I try to slide it across a surface by pushing it forward, the atom I come into contact with (the last atom in the ...
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1answer
27 views

Equations of motion acceleration doubt

So i was going through some text today morning. Where it said $$ a = \frac{vdv}{dx} $$ So they then went on to, $$ vdv = adx \\ \implies \int vdv = \int adx$$ But,I am very certain acceleration is ...
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2answers
200 views

Computing Acceleration in mass and pulley system using conservation of energy

I have a question in which a multiple pulley and mass system is being analysed. I can compute accelerations and Tension without any issue using newtons second law. However I am asked to use ...
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2answers
225 views

Find the force needed to accelerate body to a certain velocity for a certain time with respect to drag force

So, the problem is straightworward when we suggest that air resistance force is constant: $$ \vec F = \frac {\vec V_1 - \vec V_0} {t} m / b $$ $$ \vec V_0, \vec V_1 - \text {initial and final ...
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3answers
46 views

Equations of motion derivation doubt

I just started on learning how to derive the equations of motion using calculus. This is my first time and I have a basic doubt. So $v = \large{\frac{dx}{dt}}$ Then, $dx = v dt $ What does this ...
3
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3answers
1k views

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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2answers
251 views

Projectile motion - calculate landing angle

A projectile is launched at a $45^\circ$ angle, aiming for a target at a distance of 15 feet away from, and $2$ feet below the starting position. I'm looking for equations to determine: The ...
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1answer
238 views

Inclined plane, circular motion and the friction

Suppose we have a cylinder on an inclined plane of mass $m$ and radius $R$ moving without sliding (so that $\varepsilon = a/R$). Why is the friction $F$ causing the circular motion sometimes lower ...
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1answer
47 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.
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1answer
41 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 ...
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1answer
43 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 ...
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2answers
377 views

Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newton's third law and momentum conservation. Here is what I have tried. Lets take a ball mass of $m_1$ (index 1 is the ...
3
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2answers
90 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 ...
-3
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2answers
53 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 ...
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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
37 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
77 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 ...
-1
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5answers
83 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
7k 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 ...
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2answers
70 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 ...
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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
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1answer
45 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
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2answers
73 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
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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
37 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
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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 ...
0
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0answers
19 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
72 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 ...
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2answers
101 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 ...