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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How does conservation of energy differ from conservation of momentum in this problem?

Here’s a problem and how I used two approaches: https://ibb.co/r47C0gG In the problem, I’m assuming there is no friction, so all energy and momunetum is conserved How come the KE method isn’t the same ...
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Finding motorcycle turning radius based on lean angle

I have been implementing a basic motorcycle physics model and have been predicting the turning circle of both wheels based on the current angle of the front wheel. However, this fails to predict the ...
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Kinematics find time ratio

I am learning physics for my upcoming exams and have this practice question. I am stuck with this and do not know how to proceed from here. Can someone assist me? A boat travels in a straight line ...
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Why is instantaneous velocity tangent to trajectory?

Trajectory is the path of an object through space as a function of time. However, in many trajectory plots, when the movement is planar, a horizontal position axis and a vertical position axis are ...
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In Radius of Curvature calculation why do I have to assume $\text{d}^2x/\text{d}t^2=0$?

Recently, I was calculating the radius of curvature of projectile trajectories at certain points. There are two ways to do the same: Given the velocity and acceleration of the particle at some point, ...
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What direction should i exactly put for negative displacements?

If I have A....p....B....d....C points If I am initially on B and walk towards c, it's a positive displacement. Example: BC=10m east and then all of sudden I change my vector and walk to d. Is ...
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Must trajectory of an object with constant velocity angle relative to displacement be a line or circle?

Imagine you have a point object moving on the plane with its position as a function of time $$r(t)=\langle x(t),y(t)\rangle$$ Suppose that for any instant $t$ and time interval $\Delta t$, one has ...
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Finding the time period under variable acceleration

"A moves in a circle of radius $R$ such the it's tangential and centripetal accelerations are always equal in magnitude. It's inital velocity is $v_0$. Find the time period of the first ...
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What's the difference between using $a=(v2-v1)/t$ and $s=u\cdot t+1/2\cdot a\cdot t^2$?

I have a coilgun shooting a projectile at initial velocity=0. We tracked the final velocity by dividing distance (0.5m) by time (0.13s) from exit of coilgun to impact 0.5m away with a camera. So: v2=0....
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Finding the average speed of an object going down curved slides of different sizes

Say I have a slide that starts at point A which is h meters above the ground. The slide ends at point B, which is at ground level and l meters from A (horizontally). The length of the slide is L. The ...
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Shock testing equations (oversimplified?)

I'm designing a shock test tower with a maximum drop height of 1.8m. I'm adding bungee cords to add impulse and reach the intended 150G as it hits the programmer at the bottom. My question is, is it ...
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Can we have motion in systems where inertia is neglected? [closed]

According to Newton's law: $$ \sum F=ma$$ So, if we have some acceleration, it's because we have a certain amount of motion in our systems. This makes me confused if inertia was neglected. Are there ...
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Do these functions (parabolas with opposite parity) ever occur in physics?

Let's define $$f_n(x)=(n-1)\operatorname{Li}_n\left(e^x\right)-x\operatorname{Li}_{n-1}\left(e^x\right)$$ (the function $\operatorname{Li}$ is polylogarithm) $$f_{even_n}(x)=\frac{f(x)+f(-x)}2$$ $$f_{...
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Kinematics + elementary electricity question [closed]

I got this question as a bonus question in a recent physics assesment. If an electric car is travelling across a smooth horizontal road $105 \mathrm m$ long, with a battery voltage of $440 \mathrm V$ ...
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Decscribe $v$-$t$ curve (graph) for given $s$-$t$ curve(graph) [closed]

Is it possible to define the concavity of v-t curve (graph) for the given s-t curve (graph).
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How to calculate deltaV due to residual thrust

I'm trying to script a hover slam in a simulated environment using generic kinematic equations to calculate the correct throttle values I should be matching. I cut the throttle of my engine when my ...
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How to create the function of an arrow being shot?

Suppose we have an arrow that is being shot and we know the angle, starting $\upsilon_{0x}$ velocity and starting $\upsilon_{0y}$ velocity. Assuming the arrow lands on the same level as it is being ...
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Initial velocity of a body when the distance travelled by it in the last second before reaching its maximum height is $5\ \textrm{m}$ [closed]

I stumbled upon this problem recently, and it has been haunting me for more than a day at this point. The question is as follows:- When a ball is thrown up, it reaches a maximum height of $h$, ...
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How he came from the term: $L^2 - X^2 + 2Xdx = Y^2 + 2Y dy$ to $X dx = Y dy$? furthermore, how does the term $(X/Y)dx/dt = dy/dt = v'$? [closed]

I tried to solve by differente methods but wast able to achive the results in the book Could somebody exolain the authors logic?
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How many equations of motion? The higher order derivatives are highly correlated

Note: the bounty text above states "second order linear differential equations". It is an empirical observation that this is the case for the particular system I'm studying, please read &...
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How much does the Earth lag behind us when we swing?

On a swing, we pull the framework on which the swing hangs. We wriggle our body which has it's effect on the frame, which affects the Earth on it's turn (on it's swing...). It's clear that the ...
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Determine the meaning of a gradient of a graph [closed]

How do you determine the gradient of a graph in physics, such as how with a velocity-time graph, the gradient is acceleration. I want to know the general method for figuring out what the differential ...
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Measuring the curvature of the Earth using a mobile phone accelerometer + gyroscope

Suppose that you were on the surface of a sphere which is perfectly level everywhere. You are in a car or a plane, and you have a mobile phone with a gyroscope and an accelerometer that give a steady ...
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Car moving on a ball in space

Consider a car of mass $m$ moving on the surface of a ball (think of it as earth) with moment of inertia $I$, floating in a vacuum. Let the car slowly (adiabatically) drive around the circle of ...
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When does a free body moving on a smooth circular path make a complete revolution?

If we have a body like the one below , What will be the minimum initial velocity $V_0$ to complete one revolution, My assumption was that it has to reach $\theta=180$ ,But how do I describe this ...
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Graph of velocity versus time [duplicate]

The figure shows the dependence of blood flow rate as a function of time through the aorta during a single heartbeat. Assuming that the distance of the heart to the brain is 30 cm, approximately ...
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Integrating Angular Velocity Vector using Rodrigues' Rotation Formula

My understanding is that Rodrigues Rotation Formula can be used to explicitly compute an exact rotation associated with a constant angular velocity vector over a given time step. How do you derive the ...
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How do I get the velocity $v$ as a function of position $x$ from the acceleration $a$ as a function of velocity?

Suppose that a particle is moving with a non-constant acceleration on the $x$ axis of $$a(v)= Av^2+Bv+C$$ ($A$, $B$ and $C$ are constants) with an initial velocity of 0 on the x axis and an initial ...
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Is this expert report wrong about basic kinematics? [closed]

This question is about the application of kinematics in an expert report for Eirikson v. Breton, ABQB 2000 798 (archived), a judgement for a case where a woman was driving a car that was accelerating ...
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Standing Wave Equation: Why does assuming a small slope $du/dx$ not make $d^2u/dx^2$ negligible as well?

Referencing the above image, just change the label for $y$-axis to $u$-axis.^ Following the derivation of the standing wave equation: https://www.youtube.com/watch?v=IAut5Y-Ns7g&t=1324s So if ...
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1 answer
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Simple difference between module of velocity and time derivative of module of position [duplicate]

What is the conceptually difference between the two: $$\frac{d|\vec{r}|}{dt}=\frac{\vec{r}\cdot\frac{d\vec{r}}{dt}}{|\vec{r}|}\neq|\dot{\vec{r}}|\equiv \bigg|\frac{d\vec{r}}{dt}\bigg|$$ ...
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Solving and Graphing Differential Equations in Falling Motion with Resistance

In a fall motion with resistance, when the terminal velocity is greater than the initial velocity and when the terminal velocity is less than the initial velocity, the equation for solving the ...
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2 answers
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Find maximum height of a ball rolling up an inclined plane [closed]

You roll a ball up a 30° incline with an initial velocity of $10$ m/s. How far up the ramp does the ball travel? You can ignore friction. This is a problem from my physics exam review worksheet and I ...
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6 votes
4 answers
456 views

Finite distance, Infinite time?

Let's say that a ball dropped from $1 \ \text{m}$, covers $\frac{1}{n^2} \ \text{m}$ for every $n$ bounce, i.e $\sum_{n = 1}^{\infty} \frac {1}{n^2}$ so the total distance will be $\frac{π^2}{6}$, ...
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Graph of position vs time under constant acceleration [closed]

In the answer, the person showed a graph of position vs time (for constant acceleration), his graph looks like $$x\propto t$$ but in reality, $$x\propto t^2$$ under constant acceleration. Isn't his ...
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Motion of free fall [duplicate]

We know that according to law of free falls object, all bodies fall with the same constant acceleration. But in distance formula ($s = \frac12 gt^2$), why the acceleration is just half?
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Calculating the displacement of particle as a function of time

I got this interesting question from a FB parents group: A particle $P$ moves along the $x$-axis int eh direction of increasing $x$. When the displacement of $P$ from the origin $O$ is $x$ $m$, its ...
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What is displacement time graph for this object which is in $xy$ plane going in sine wave like path from A to B. Also can velocity constant in path?

The path is from A to B in sine wave curve while the displacement is straight line.So how displacement is calculated for graph purpose here
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End motion of an empty spherical shell with a ball rolling on it's inner surface

Let's picture an empty sperical shell in inter galactic space or beyond. Inside this shell, a ball is rolling on the inner surface. Because of friction and the centrifugal force the ball exerts on the ...
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How, if, does the inside air of a football influence it's motion?

And before me lies a football. Say it's filled with pressurized air. If I kick it, how will the inside air be influenced? Will the kick induce soundwaves? Can the ball give a sound? Will it influence ...
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If we put a number of identical boxes on top of each other and apply a linearly increasing force to the bottom, will they start slipping one by one?

Let's imagine the following scenario. I put a number of identical boxes on top of each other. I then apply a constant jerk to the bottom box. What will happen? Will the start to slip one by one? The ...
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Can an object move with a constant velocity without balanced forces?

Can an object move with a constant (magnitude) velocity without the balanced forces? As an object which is balanced with the frictional force continues moving at a constant velocity, acquired till ...
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5 answers
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How does a sliding object stop moving by the effect of kinetic friction, if kinetic friction is constant and Fk can't be greater than Fapp on its own

The kinetic friction is constant. So if say, I apply a force of 20N on an object and the kinetic friction is 13N, then how does the object stop moving after some seconds. I believe that kinetic ...
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4 votes
5 answers
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Can't understand a statement about motion

From the book where I am studying motion, It says Motion is a combined property of the object under study and the observer. There is no meaning of rest or motion without the viewer. I know that, for ...
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Can a frame still be an inertial frame if its center varies with time relative to a “true” inertial frame?

Picture a seat on a Ferris wheel. Neglecting any rocking, is the seat of a Ferris wheel an inertial frame? My guess is that yes it is right? The frame itself isn’t rotating or accelerating relative to ...
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10 votes
7 answers
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What is the instant velocity? [duplicate]

The velocity is the variation rate of the position correct? So does it make sense to talk about velocity without time?
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Changing velocity even when acceleration is zero

Consider a particle performing circular motion with position given by $$\vec r=r_0e^{\beta t}\hat r$$ such that $\dot\theta=\omega$, is a constant. The velocity becomes $$\vec v=\beta r_0e^{\beta t}\...
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Why doesn't an air valve move automatically when placed on a zero friction surface?

Air pressure is actually a force experienced by the surface of the container when air molecules hit it in high speeds. An air valve opens and allows air to move in one direction and blocks the the ...
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Why do kinematic equations only work with constant acceleration?

People say that the equations are derived assuming a constant acceleration. I just don't see how this is the case. (I am new to calculus.)
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Why do equation of motion fail to apply in non-inertial frame even after applying pseudo force?

I considered two cars of equal mass moving towards each other with speed 30m/s and 18 m/s respectively and when they are 100 meters apart they both start de accelerating at 6m/s² each. So if we ...
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