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.

Filter by
Sorted by
Tagged with
0
votes
2answers
502 views

Ackermann Steering Angle

Given the position of the vehicle ($x,y$) at different time points, the speed of the vehicle (m/s), the direction the vehicle is facing (heading — in degrees), the track width of the vehicle, and the ...
0
votes
3answers
211 views

Are acceleration and velocity simultaneous? [closed]

I would think yes because, if a rope tied to a swinging rock breaks, the rock flies off in the direction that is perpendicular to the direction of the last instant of the acceleration. The ...
0
votes
1answer
110 views

Range of a projectile as a function of launch angle [closed]

Goal: Derive an equation for range of a projectile as a function of launch angle if it started from a height > 0 and landed to height = 0 I know that the horizontal range $$ R = \frac{v_0^2 \sin2\...
-1
votes
1answer
790 views

What's the formula for the speed of an accelerating car?

I am trying to find a formula that closely describes the speed of an accelerating car over time. I have found many graphs on the internet, but so far no formulae to generate them. For my purposes I ...
-2
votes
1answer
88 views

How to know when to divide what components and equate them in dynamics of circular motion? [duplicate]

Here's what I'm trying to say: Why did we equate $mg\cos\theta = T$ instead of: Why is $T\cos\theta = mg$ incorrect? How do I know when to divide which components? like I could've equated $T\cos\...
-2
votes
1answer
96 views

When one kid runs into another and they bump heads, why is the slowest mover in most pain? [closed]

In my experience, if one kid runs really fast and accidentally bumps into a second kid who's standing still, and they bump heads, the kid who was 'standing still' (relative to earth) always seems to ...
-12
votes
3answers
2k views

What would happen if an unstoppable force hits an immovable object? [closed]

I realize that the question a rather large paradox, but I do wonder if such a thing were true what would happen, assuming that neither of these "objects" can be destroyed by each other?
6
votes
2answers
255 views

View from a helicopter rotor: why is the horizon distorted?

This video ("rotor panorama") was captured by a camera attached to the rotor head of a radio-controlled helicopter, with the frame rate set to the rotor's frequency. During a long segment of the video,...
6
votes
2answers
2k views

Why do we equate an indefinite integral to a specific value?

Suppose we want to obtain a displacement vector defined as $\mathbf s(t) = x(t)\mathbf i + y(t)\mathbf j + z(t)\mathbf k$ from the components of a velocity vector $\mathbf v(t) = \dot x(t)\mathbf i + \...
6
votes
3answers
256 views

Does $y$-motion really have nothing to do with $x$-motion?

I am watching a Physics 1 for physical science majors on coursera.com, and in one of the concept tests there is a question that goes like this; "A bullet is fired horizontally from a rifle on the Moon ...
5
votes
3answers
391 views

If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?

Of course aerodynamics factors into this question, and the faster you are moving the more air you have to push out of your way, the more energy you use. But would the difference be only a small ...
5
votes
2answers
267 views

How long does it take to optimally change position and velocity?

A spaceship moving in two dimensions is at position $(x, y)$ and has a velocity $(v_x, v_y)$. It also has a maximum acceleration $a_{max}$. Its goal is to be at position $(x', y')$ with a velocity of $...
5
votes
3answers
593 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 $\dfrac{dx}{dt}$ ...
5
votes
2answers
562 views

How is water able to bend around corners and violate the laws of inertia?

When I roll over wet pavement with my scooter it apparently flicks up onto my back. However, the angle between the wheel and the rear fender is -3 degrees. How is it possible for the water to be ...
4
votes
2answers
233 views

Most fundamental reason for Newtonian KE loss being invariant in inelastic collisions

This answer to a question about why Newtonian kinetic energy is quadratic in velocity shows that if an inelastic collision's KE loss is invariant under Newtonian boosts it has to quadruple when ...
3
votes
2answers
227 views

How can a player hit a home run with a broken bat?

Although they're rare, I've seen a few instances where a baseball player breaks their bat and still manages to hit a home run. Two examples: Chris Davis from the Orioles did it in 2012 (https://www....
3
votes
4answers
1k views

In perfect vacuum (no external force), if I apply a small amount of force to a body, will it continue to accelerate forever?

According to the equation $F = ma$, the greater the force applied to a body, the greater its acceleration. But in a place where there is no gravity or any other kind of external force, if I apply a ...
3
votes
3answers
2k views

How would you move without gravity?

I'm wondering how would you move without gravity? You would still have air pressure at 1Atm. Would you "swim" in the air or would you have do something else?
3
votes
2answers
298 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 ...
3
votes
2answers
2k views

Time reversal in simple *solution* to equation of motion

Consider the solution to the equation of motion for a particle with a constant acceleration: $$ x(t) = x_0 + v_0t + \frac{1}{2}at^2.$$ If I let $t \rightarrow -t$, then the equation becomes: $$ x(-t) ...
3
votes
3answers
2k views

Distance travelled in free-fall

When an object is in free fall, we have: $$a(t) = g - \frac{c}{m}v(t)^2$$ where $g$ is acceleration due to gravity, $m$ is the mass of the object, and $c$ is the coefficient of air resistance. How ...
3
votes
1answer
206 views

Hypothetical special relativity with mass conservation [closed]

I thought of this question while studying inelastic collisions in special relativity, where kinetic energy is converted into mass-energy. I was wondering if it's possible to formalize a version of ...
2
votes
1answer
811 views

Why do three particles placed at the vertices of an equilateral triangle, moving along the sides, meet at the centroid?

I just read an example of vectors in my book which is confusing me. Three particles A,B and C are at the vertices of an equilateral trinagle ABC. Each of the particle moves with constant speed v. A ...
2
votes
4answers
502 views

Can we do a thought experiment to prove that the horizontal and vertical motion of a projectile are independent of each other?

It seems really hard for me to grasp the idea that horizontal and vertical motion of a projectile are independent of each other. Intuitively I feel that they should affect each other. How can it be ...
2
votes
6answers
2k views

Formula to determine acceleration based on constant energy input

I'm a software engineer building a simulator for train movement. What I would like to do is create an acceleration curve that's closer to reality. This is my thinking, which includes some ...
2
votes
2answers
47 views

How is torque transmitted between inclined surfaces?

In the picture below, in a), a body K1 is pivotably attached to a bearing. My question is about the torque that results from a force exerted onto a surface of the body K1. A first force F1 applied ...
2
votes
4answers
16k views

How to find tangential/radial/angular velocity for motion in any curve? [closed]

Is the radial velocity responsible only for changing distance between objects and the component perpendicular to it only for change in direction? If so why? Please try to give a different explanation ...
2
votes
3answers
3k views

For circular motion in a vertical plane, why does Net Force = Centripetal Force?

I'm struggling with some of the concepts pertaining to the forces and acceleration associated with circular motion in a vertical plane (only concerned with what happens at the 'top' and 'bottom' of ...
2
votes
1answer
109 views

Rotational motion from curved slope?

So I've learned for any slope with a sliding object, say a box, the speed at the bottom only depends on the height it was dropped from because of conservation of energy, assuming absence of friction ...
2
votes
3answers
678 views

Does a constant 4-acceleration implies constant acceleration?

Before asking the question I explain here my line of thoughts: I'm almost sure that a constant acceleration $\bf{a}$ implies constant 4-acceleration $w^\mu$. So I assume constant acceleration, then, ...
2
votes
2answers
104 views

Angular velocity as $r \to 0$

I know that angular velocity is defined as the rate of change of angular displacement and is related to tangential velocity via $$\omega = \frac{r\times V}{|r^2|}$$ My question is what will be the ...
2
votes
2answers
2k views

Displacement vs. Distance

I'm new to physics, and I just learned what velocity is. From what I learned, velocity is, displacement/time. But, I'm confused about what displacement and distance is, and how is affects velocity. So,...
2
votes
1answer
784 views

The norm of the vector sum of two 4-momentum vectors before and after pair production

Two photons traveling along the x-axis (in a lab frame of reference) of different frequencies are about to collide. Their 4-momentum vectors are (h$\nu_1$/c , h$\nu_1$/c , 0, 0) and (h$\nu_2$/c , -h$\...
2
votes
0answers
77 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 ...
2
votes
5answers
1k views

Why is it said that speed always remains constant in circular motion?

One can cover circular motion with different speeds at different positions, right? The only aim is to complete his circular motion, right?
2
votes
5answers
409 views

Instantaneous velocity

So here’s a question I’ve been thinking of for a while. Suppose we say, “an object is having an instantaneous velocity along a particular direction ( say 10 m/s along the $x$-direction)” . Is it fair ...
2
votes
2answers
251 views

Velocity of a ring tied to an inextensible rope

In the diagram, the pulley is weightless and friction less and the thread connecting the pulley with the ring is inextensible. The thread is attached to the ring which in turn can move only ...
2
votes
1answer
837 views

Relativistic kinematics of particle decay

Suppose a particle decays to three other particles. The masses of all particles are assumed to be known and we work in the rest frame of the parent particle. So there are 12 parameters for this ...
2
votes
1answer
14k views

Determine acceleration from experiment (Newton 2nd Law)

I have done a physics experiment (setup below). And was asked to determine the experimental and theoretical acceleration. The data I've got Ok, am I right to say Experimental acceleration = $2(...
1
vote
2answers
2k views

Average acceleration versus instantaneous acceleration

Does instantaneous acceleration also changes when direction of velocity changes. I know average acceleration does change.
1
vote
1answer
114 views

Writing source four velocity for Lorentz boosted frame

I am trying to derive the source four velocity for Lorentz boosted frame. If the source four velocity for rest frame is denoted as $U^{\alpha} = (1, \bar 0)$, then how do I write this $U^{\alpha}$ for ...
1
vote
2answers
1k views

Why does the Fluid inside a Water Balloon Continue to Move even when the Balloon Being Pulled has Stopped?

If there is a rubber balloon filled with water attached to a string, and the string is pulled in 1 direction, causing the balloon to also be pulled, why does the water inside continue to move even ...
1
vote
2answers
2k views

Why can't some light ever reach earth? [duplicate]

Note: I'm a layman in physics. Excuse me if this question is a duplicate, I lack the knowledge in technical terms to find the answer to this by research (I've tried). Let's suppose there's a star ...
1
vote
2answers
137 views

Acceleration: Value Disparity?

If we consider a ball moving at an acceleration of $5\ \mathrm{m\ s^{-2}}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5\ \mathrm m$. In the 2nd second will $5\ ...
1
vote
2answers
304 views

Rocket faster than light?

In this article, wikipedia describes a constantly accelerated rocket, assuming special relativity : $$ x(\tau) \;=\; \frac{c^2}{a} \left(\cosh \frac{a \ \tau}{c} -1 \right) $$ The proper time $\tau$ ...
1
vote
3answers
343 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 ...
1
vote
1answer
74 views

Does distance matter for gravitational U in non-earth/ non-celestial-body systems?

Gravitational U = -Gm1m2/r, thus the distance (r) the two carts are apart affects how much U you end up with, no? Thus it also affects whether or no ME is ultimately conserved, because you can just ...
1
vote
1answer
106 views

What does it mean by $t=-1$?

if the position vector of a particle is $\hat{r}=\left(4+3t\right)\hat{\imath}+\left(t^3\right)\hat{\jmath}+\left(-5t\right)\hat{k}$, i want to find at what time this particle passes through the point ...
1
vote
2answers
19k views

If I lift a box vertically, why is the work I do equal to the distance I lift it times the force of gravity on the box? [duplicate]

I have problems fully understanding the concept of work, so please forgive me if this is simple. If I take a box of mass $ m $, and lift it a distance $ d $ vertically, why is the work I have done ...
1
vote
1answer
56 views

Intuitive explanation for the second solution. Projectile problem [closed]

Take the classic problem of a person standing on a high building/cliff and throws an object which follows a parabolic path to the ground. Solving this problem gives two solutions for the time in which ...

1
4 5
6
7 8