# 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.

4,193 questions
Filter by
Sorted by
Tagged with
41 views

### Expressing a specific motion from the point of view of a different rotating coordinate system [closed]

Simplified problem presentation I am trying to describe a specific motion from a point of view of a moving coordinate system. To make easier the comprehension I created this childish animation, where ...
19 views

### Determining the position of a particle directly in terms of the force that acts on it [closed]

I was given this homework assignment and I had a particular approach but it is not the intended solution. A particle of mass $m$ starts at rest, $x=0$, and at $t=0$ is acted on by a force $F(t)$. ...
45 views

### ${}$ Projectile motion

Basically we take the value of acceleration due to gravity as -ve ($-g$),when an object is thrown in the opposite direction of $g$. But in projectile motion the object first opposed the g and travels ...
22 views

### Constraint relations problem (High school physics) [closed]

I have solved similar problems by relating their displacements and differentiating with respect to time to find their velocities, but how do I solve this?
39 views

### Calculate Maximum Velocity with Time Constraint [closed]

I've been trying to get this question posted here since yesterday but it keeps getting closed. I promise, this is a relevant question to physics. I am a computer scientist without a robust background ...
31 views

### Could she save a dog which was 30m away from her? [closed]

Sheela is moving on a street highway on her bike with speed of 20m/s. She applies brake at full length and her bike comes to rest after covering 20m distance. If her speed had been 40m/s could she ...
14 views

### Complex solution in equation of motion [duplicate]

When I tried to solve some motion questions, I got complex numbers for time, displacement, etc. And my teacher said my answer was correct. Is it possible to have a complex number solution in the ...
36 views

### What does heat do to atoms? [closed]

If infrared energy is absorbed as velocity and not a force, is it the electron spin that is absorbing as seen by frequency? How does it work for increased velocity, could it work to decrease velocity ...
51 views

### How do I solve for distance in the $x$ when only given the radiant velocity and the angle above the horizontal?

I recently had a physics test in AP physics one algebra based that my entire class failed. It was full of questions like this: A projectile is launched from a level surface toward a cliff. At launch, ...
21 views

### Adding vectors question gr12 physics [closed]

A car traveling 60km/h heads West for 10 minutes. It then enters the highway and speeds up to 100km/h heading 35 West of North for 20 minutes. As it exits the highway, it slows down to 50km/h [W80N] ...
44 views

### How many relativistically invariant degrees of freedom in $n$-particle scattering?

Suppose we have a scattering process with $n$ external legs with four-momenta $p_1, \cdots, p_n$. Naively there are $4n$ degrees of freedom, however most of these putative degrees of freedom are not ...
44 views

### Kinematics - confusion about signs of angular velocity and acceleration (general rule ?) [closed]

I have often found it challenging to determine the direction of angular velocity and acceleration in exercises involving rotational motion, much like the one depicted in the picture below. While ...
36 views

### Velocity to Acceleration negative line [closed]

Is the velocity line in below 0 is a different acceleration line? For example from 0 - 6s and from 10 - 17s. It has the same slope.
1 vote
21 views

### Decay rate with specific helicity in rest frame and lab frame

Consider a two-body decay, such as the pion decay: $\pi^+\to \mu^+ + \nu_\mu^{}$. In the Standard Model, as there only exits left-handed massless neutrinos, the helicities of final particles are known....
20 views

### Formular of acceleration in Non-uniform circular motion [duplicate]

This upper image is from the textbook of Halliday-Fundamentals of Physics. It demenstrates how we get the formula of $\vec{a}$ in uniform circular motion. Here is content from Douglas C. Giancoli--...
12 views

### Finding the greatest distance reached above the ground [closed]

I don't understand why there is an additional $0.441$ added to the final distance... I do understand that the distance travelled by $A$ downwards is equal to the distance moved by $B$ upwards but why ...
61 views

### The direction of net force in circular motion

The small ball attached by a thin string is in uniform circular motion as shown in the picture (vertical plane). There are two forces acting on the ball, Gravitational force $F_g$ and Tension force ...
117 views

### Derivation of equations of motion using vectors

I was trying to draw the motion of a point mass given an initial position, velocity and constant acceleration. I figured that the change in position $\Delta \vec{r}$ over an interval $\Delta t$ would ...
88 views

### Why does $\vec{a}=\vec{\omega}\times \vec{r}$ as well as the velocity does?

Today I came in class and in one of the problems the teacher used $\vec{a}=\vec{\omega}\times \vec{r}$ which made me very confused because I don't know where it comes from, it seems pulled out of thin ...
47 views

### Why is the distance negative in a kinematic equations? [closed]

A rocket with zero initial speed takes off at a speed of 100 meters per second, assuming that gravity is 10 meters per second squared, determine the distance travelled: $$v_f^2 = v_i^2 + 2ay$$ ...
68 views

### Reality of speed and time [closed]

I have a very simple question. How does a faster object takes less time for the same distance? A car with a speed of 100km per hour takes one hour to travel 100km while a car with the speed of 50km ...
33 views

### Relationship between tangential and angular acceleration in 3D

In 3D circular motion, $\vec v=\vec \omega \times \vec r$, then the tangential acceleration is \begin{eqnarray*} \vec a_t =\frac{d \vec v}{dt} & = & \frac{d}{dt}(\vec \omega \times \vec r)\\ ...
53 views

### Why do I get $\alpha = \omega ^2$ in angular acceleration?

In a 2D plane, the tangential acceleration of an object moving in uniform circular motion is, using the fact that $v = \omega r$ : $$a_t = \frac{v^2}{r} = \omega^2 r$$ and we know the relationship ...
1 vote
45 views

### Question related to pathfinder kinematics [closed]

In the given question I am able to answer that v = 20m/s as in a circle at the diametrically opposite points the direction of velocity will be opposite hence they will add up to give 2v =40m/s hence v=...
48 views

### Why is throwing a bullet by hands not effective as using a gun? [duplicate]

The bullet when fired applies equal and opposite force to the Gun, (Newton's 3rd law) Thus to keep the gun stable we apply some force which should be equal to the force applied by the bullet. If we ...
80 views

### Hyperbolic motion in Rindler coordinates never crossing the origin

When we have a constant proper acceleration with $a_{\mu}a^{\mu} = g^2$ in the $x^1$ direction of some inertial frame, then $$t = g^{-1}\sinh(g\tau),$$ $$x = g^{-1}\cosh(g\tau)$$ and the world line ...
53 views

### Can we relate newton's second law and kinematics equations? [closed]

Specifically, If vi = 0, then a = vf^2 / 2s [ s = distance travelled] And from newton's 2nd law, a = Fnet / m [ m = mass of object] But I've tried to them on a bunch of different problems, and they'...
60 views

### Meaning of relative rapidity

What is the meaning of relativity rapidity? I know that the rapidity of a particle in general is defined as $\text{tanh}^{-1} \left( \frac{v}{c} \right) = \phi$. I encountered a problem that talks ...
35 views

126 views

### 2d collisions of perfectly elastic circles with mass

My question is about 2 circles colliding. I can't describe it perfectly, which is part of the reason I'm stuck. Here is a picture. There are 2 circles. They both have an initial position, velocity, ...
32 views

### How to find travel time using a velocity matrix $vel[x][t]$?

I have a velocity matrix which depends on both position $x$ and time $t$ i.e. $vel[x][t]$. How can I calculate the travel time between two points $x1$ and $x2$? How do I implement t = \int_{x1}^{x2} ...
1 vote
38 views

### Why do spheres indented by a curve follow the curve when later rolled on the same curve?

In this Youtube Short it was mentioned a way of constructing a shape that followings any curve one could draw. Apparently the motivation to construct it is to do the following, roll a sphere of clay ...
39 views

### Is it possible to determine free surface velocity experimentally of the liquid rotating in a cylinder?

Hello Physics StackExchange Team, I want to know whether it is possible to experimentally determine the velocity at which the free liquid surface is moving/rotating in a cylinder with a rotating disk. ...
17 views

### Force magnitude and direction to maintain constant speed on given trajectory

In circular motion to maintain a constant speed on a fixed circular path the force required has magnitude mv^2/r and is directed toward the centre of the circle. How would this magnitude and direction ...
33 views

### I need a ship at rest to accelerate under preferably constant acceleration/deceleration to arrive at rest at an object 55 AU away [duplicate]

I'm working on the story and I need help with the plot point. Assume that the energy needed for constant acceleration is not a problem. And there's no need to complicate this with outside forces. I ...
49 views

### Velocity as a scalar quantity in regards to KE

As the title would imply, I’m questioning why velocity is considered a scalar value when measuring the kinetic energy of a system. From my understanding, it’s a result of it being squared in the ...
267 views

### Photon Doppler shift and Lorentz invariance

My understanding is that the energy of a photon depends your your reference frame because the energy of a photon depends on its frequency and its frequency may get Doppler shifted. Now, I am trying to ...
69 views

### Using Mandelstam Variables in Experimental Data

I am reading an article of Veltman and Lemoine from 1980 on radiative corrections to $e^+ e^- \rightarrow W^+ W^-$ in the Weinberg model. In Section 3, they work at tree level and write down the ...
142 views

### Linear algebra based proof of circular motion formula. How do I get a by itself on the LHS?

I haven't taken a course on linear algebra, but I know the very basics and started watching 3blue1brown's series on it as I will be taking it this spring. While watching the series, I realized I could ...
1 vote
15 views

### Discontinuities in the $u$ channel

if we consider a 2-to-2 scattering, we have normally an $s$ channel a $t$ channel and $u$ channel. In CMS frame $s$ is positive and $t$ and $u$ negative, by crossing symmetry there are kinematics ...
1 vote
40 views

### Clarification to questions about friction and cars [closed]

I'm trying to understand how car wheels work. In a perfect world the bottom of the wheel has no velocity. The wheels are in a state of pure rolling, which means there is no static or kinetic friction ...
20 views

### Doubt in displacement time graph for a body moving with constant, negative velocity

This is a displacement - time graph of a body having constant, negative velocity. As we can see, the angle $θ$ (in anti - clockwise direction) is greater than $270^\circ$, and lesser than $360^\circ$,...