Questions tagged [kinematics]

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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166 views

How long does it take for a balloon to deflate?

Since gas flows from an area of high pressure to low pressure, upon opening an aperture on say a balloon one would expect the contents to diffuse out until both the inside and outside reach a pressure ...
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1answer
639 views

Exertion from swinging on a playground swing

I've read about how by tilting one's body one changes one's center of mass while swinging on a playground swing, and thereby increases the energy of the swing. But I would like to get a better sense ...
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2answers
8k views

Position in circular motion

Is it possible to determine the position of a particle undergoing circular motion, in x-y coordinates, at any given time and velocity? I'm thinking it has something to do with $\pi$
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2answers
636 views

The force causing galaxies to accelerate away from each other?

The galaxies in the universe appear to be accelerating away from each other according to the Doppler shift that is present in the light we receive from other galaxies. According to Newtonian ...
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2answers
93 views

comparing highway car collision

Is there a difference in the impact force in this two cases? A car driving at 100km/h crashes a truck standing still on the road The same car driving at 200km/h crashes the same truck from behind, ...
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3answers
42 views

Kinematics: Circular Motion

What is the difference between angular velocity and angular speed? Is angular velocity after one complete rotation zero? Is the magnitude of angular velocity always equal to angular speed?
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1answer
101 views

Maximum Momentum of Neutral Pion

I'm considering the reaction $p + p \rightarrow p + p + \pi^0$. To find the maximum momentum that the $\pi^0$ can have after this reaction in the center-of-mass frame, what I am doing is assuming the ...
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1answer
71 views

Kinetic energy in different frames [duplicate]

I have an electric bike moved by a battery. I am at a train station with two friends. A flat train car platform passes by at $1 m/s$. The friend #1 jumps on it while the friend #2 remains at the ...
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2answers
2k views

Why do objects seem to move faster (relatively) when they move tangential to the observer?

I've observed this loads of times while travelling, in cars, trains,etc.I can't quite put it in words and therefore I've roughly made a diagram to assist my question. Assume an observer is travelling ...
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2answers
415 views

What moves an object? Momentum or Kinetic Energy? [duplicate]

What exactly makes an object move? Momentum is $\vec p= mv$ where $m$ is mass of an object and $v$ is the velocity of an object, and as a result of this when I fire a bullet the bullet may travel much ...
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1answer
48 views

How to estimate minimal efforts required to update trajectory of a moving ball?

Let's imagine we've got a uniformly sampled curved trajectory of a moving ball in 3D space without gravity. Let's assume that some dynamic force is applied to the moving ball to update its trajectory ...
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3answers
6k views

Very basic question: When to use $s=vt$, $s=1/2vt$, $s=at$ and $s=a/t^2$?

Very basic question: When to use $s=vt$, $s=\frac{1}{2}vt$, $s=at$ and $s=\frac{a}{t^2}$? What was the difference between those?
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7answers
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Why will a dropped object land at the same time as a sideways thrown one? [duplicate]

My textbook says that a ball dropped vertically and a ball thrown sideways will not only both land simultaneously but their height will be corresponding for the entire fall, as shown in a diagram ...
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2answers
1k views

Acceleration during collision with ground

For my physics class, I have to calculate an objects acceleration while it came to a stop. It was traveling at $6.26\: \mathrm{\frac{m}{s}}$ at impact, and travels a distance of $0.025\: \mathrm{m}$ ...
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1answer
1k views

Is the Coriolis acceleration formula just an approximation?

The Coriolis acceleration given in textbooks is: $a_{cor} = -2\omega v$ When trying to understand the derivation, it seems as though this is just an approximation. And to illustrate this I give a ...
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2answers
142 views

Question about derivation of four-velocity vector

In order to describe a notion of rate of change of positon, in four-dimensional spacetime, we have to introduce the concept of four-velocity. So, consider the following: For a massive particle ...
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1k views

Free fall and projectile motion

I'm wondering if something is falling say from a roof, would the distance it falls be the final $y$ position? Also would all the $y$ components (velocity, displacement) be negative?
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Rigid (planar) Multibody system: How are these equations of motion linked to the model?

This a second question I have on the same subject as my previous question, so I will make a link here (Motion equations for Woodpecker toy (multibody system)) to that question (and a link from that ...
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2answers
81 views

Kinetic energy in work energy theorem

What is the difference between kinetic energy and change in kinetic energy? Wouldn't the change in kinetic energy give a result which is a kinetic energy and if the change in kinetic energy can be ...
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1answer
23k views

Calculating angle of projectile motion [closed]

I realize that similar questions have been asked but I'd like to put my problem here and what I have to make sure everything is right. So my problem is: I've got a rock $2.5$ meters above the ground ...
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1answer
605 views

Finding Acceleration Force of Gravity on Rotated Accelerometer

Is it possible to calculate the force of gravity on the $x$, $y$, and $z$ readings of an accelerometer if I know the rotation of the sensor? If so, how would I do this? Sorry if I am doing this wrong,...
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1answer
62 views

cross over to another object that has same height with our last position, is that really possible?

I have got confused with this. Well..In that picture, lets say the height is 8m, and the car moves and going to cross over to another object that has the same height with its last position..my ...
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3answers
11k views

Solve for Initial Velocity of a projectile given Angle, Gravity, and Initial and Final positions?

I've found equations http://www.physicsclassroom.com/Class/1DKin/U1L6a.cfm for solving everything (and rearranged to solve everything) to do with projectile motion EXCEPT this, even though it should ...
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1answer
3k views

Relativistic Kinematics - 2-Body Particle Decay

Consider the scenario where a particle of mass $M$ decays into two lighter particles of mass $m_1$ and $m_2.$ In the center of mass frame (i.e. $\mathbf{p}_1$ and $\mathbf{p}_2$, the momenta of the ...
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2answers
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Depth of a well

A climber wants to know the depth of a well. He drops a rock and 4 seconds later he hears a noise. The speed of sound is 340 m/s. Okay, so $ t= 4s $ But t has 2 parts, $ t = t_1 + t_2 $ Because ...
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2answers
128 views

What to call an object which is in motion but not accelerating?

I began learning about acceleration and according to the source i learned from an object only accelerates when there is change in vel. &/ direction... what i am wondering is what do you call it ...
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1answer
77 views

A pearl that moves in a smooth vertical hoop (Circular motion) [closed]

I couldn't understand something about the situation of a pearl that moves in a smooth vertical hoop in circular motion. When the normal force equals 0 , the pearl didn't disconnect from the smooth ...
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1answer
77 views

Powered interception of a moving object

I want to intercept two objects, making both their time and velocity the same. One has acceleration to achieve this goal, while the other is moving at a constant rate. Furthermore, I want them to ...
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0answers
428 views

Equation of motion of a free particle

We know that the equation of motion of particle can be derived from the respective action. But in the book I am reading, the author is saying: ... timelike worldline of a massive particle is ...
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1answer
858 views

Trajectory of a projectile in a three dimensional space [closed]

$g$: the gravitational acceleration—usually taken to be $9.81\:\mathrm{m/s^2}$ near the Earth's surface $θ$: the angle at which the projectile is launched $v$: the speed at which the projectile is ...
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1answer
89 views

General formula for relativistic Energy/momentum conservation?

Say we have a particle of mass $M$, which is at rest in a laboratory. This particle then decays into a particle of mass $m$ and speed $v$ and a photon of frequency $f$. How would one describe the ...
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3answers
1k views

If we move from one point to another with constant speed/velocity will the work done be zero or not?

We know that work done is change in kinetic energy, but when the speed is constant the work done must be zero, I guess. Am I right or wrong?
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2answers
219 views

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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4answers
379 views

Is $\left|\frac{d\vec{r}}{dt}\right| = \frac{d|\vec{r}|}{dt}\;$?

Is magnitude of instantaneous velocity same as instantaneous speed? More specifically, is $$\left|\frac{d\vec{r}}{dt}\right| = \frac{d|\vec{r}|}{dt}\; $$ Also Is it wrong to say that $\dfrac{d|\vec{...
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1answer
14k views

Calculate acceleration and time given initial speed, final speed, and travelling distance? [closed]

A motorcycle is known to accelerate from rest to 190km/h in 402m. Considering the rate of acceleration is constant, how should I go about calculating the acceleration rate and the time it took the ...
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1answer
1k views

Rocket projectile motion problem [closed]

I'm not really sure where to start with this question: In a brisk wind from the south-east of $14.1\:\mathrm{m/s}$ a rocket pointed due north is launched from a cliff that is $500\:\mathrm{m}$ above ...
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1answer
80 views

How is a wave function applied to predict the path of a particle?

The wave function's argument is position, but can the position of a particle be predicted from the wave function? Specifically, can the wave function allow you to find the equations of motion for a ...
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1answer
72 views

Kinematics Issue w/ negative Velocity [closed]

Given: $$Y = v\sin(\theta)t-\frac 12 gt^2$$ $$D=v\cos(\theta)t$$ Thus: $$\frac{D}{v\cos(\theta)} = t$$ Substituting we get: $$Y=v\sin(\theta)\frac{D}{v\cos(\theta)}-5\left( \frac{D}{v\cos(\...
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1answer
5k views

Throwing an object in the air [closed]

Studying formulas about velocity and acceleration I came up with a question: if I throw an object in the air with a velocity $v_0$ (suppose i throw it vertically) in how much time its final velocity $...
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3answers
1k views

Projectile Motion with air Resistance - Adjust only the Angle to hit a target

OK, let me preface this by saying i am not a physics student, nor have i ever been. I am a software engineer working on a development degree. So this is homework but the assignment was just to create ...
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1answer
46 views

How to express in terms of spacetime intervals the average speed of one participant having moved between two suitable others

Given a flat region of spacetime as set $\mathcal S$ of events together with values of spacetime intervals (up to a common non-zero constant) for each pair of events, $s^2 : \mathcal S \times \mathcal ...
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1answer
260 views

About how much force would something have to exert to be effectively unstoppable? [closed]

Assuming an object is moving in a straight line propelled by a force. How much energy would that force have to exert so that there are no known forces or objects that could stop it from moving in that ...
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1answer
685 views

Is the term “deceleration” ambiguous? Does it refer to negative acceleration, or is it something else entirely? [closed]

What does that term truly mean? Sometimes it confuses me what exactly it refers to.