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 this chair move?

I have a chair like this(shown in figure). I was kneeling on the part where we sit. I just gave a sudden push to the part where we rest the back, without moving my legs. I found that the chair is ...
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How can an object with zero acceleration move?

My physics text has a problem in which it is said that a person moves a block of wood in such a way so that the block moves at a constant velocity. The block, therefore, is in dynamic equilibrium and ...
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Does an airplane's speed include the speed of the Earth?

After take off, does airplane's speed include Earth's movement/speed? Do airplanes turn with Earth movement/rotation?
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Kinematics question - Newton's Law of Motion [closed]

Question: Find the mass M of the hanging block in the following figure which will prevent the smaller block from slipping over the triangular block. All the surfaces are frictionless and the strings ...
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4th kinematic equations for constant acceleration

Ive been given the 4 kinematic equations for constant acceleration. The fourth being: $$s=ut+\frac{1}{2}at^2.$$ If rearranged it forms the quadratic equation $$at^2+2ut-2s=0.$$ But that means that ...
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How to get the four-velocity components from a given metric tensor?

I’m a little bit confused about how to get the four-velocity components from a given metric tensor (or line element). For instance, which are the components of the four-velocity in the Schwarzschild ...
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Calculation of Distance from measured Acceleration vs Time

I have an Accelerometer connected to a device that feeds the instant values of the acceleration in the 3 directions. I've tried to calculate the distance for a vertical movement using these values ...
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1answer
354 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 ...
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Why does gravity assist transfer twice the planet's velocity?

In orbital mechanics and aerospace engineering a gravitational slingshot (also known as gravity assist manoeuver or swing-by) is the use of the relative movement and gravity of a planet or other ...
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Why do these two ways of understanding constant acceleration give different results?

I have a question pertaining to the concept of acceleration and it's formula - Both seem to give me different answers. I was asked: A train is moving at a velocity of $20\ \mathrm{m/s}$. It hits ...
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Can we divide a vector by another vector? How about this: $a = vdv/dx?$

My physics teacher told us that we can’t divide vectors, that vector division has no physical meaning or significance. How about this: $$a = vdv/dx.$$ It says acceleration vector equals velocity (as ...
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Does the logarithm of a non-dimensionless quantity make any sense?

A train consists of an engine and $n$ trucks. It is travelling along a straight horizontal section of track. The mass of the engine and of each truck is $M$. The resistance to motion of the engine and ...
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Why isn't average speed equal to displacement over time?

I'm in an introductory Physics course and I need help! During a one-hour trip, a small boat travels 80.0km north and then travels 60.0km east. What is the boat's average speed during the one-hour ...
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If an object moved 5 meters in a second, how can its velocity be 10 m/s? [duplicate]

On physicsclassroom.com, an assignment gives data for an object experiencing acceleration: This is the corresponding chart for the object's velocity: At $0$ seconds the position of the object is $0$...
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Extracting the 3D coordinates of a moving object from a video

Take a look at these two pictures, which are stills from a video which demonstrates magnus effect in football: I want to extract the coordinates of this ball in 3D space from this video. These are ...
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Is a heavier skier faster? [duplicate]

Is it true that a heavier skier goes faster? If it is, why is that? My intuition would be that the speed gained by a skier should be independent from its mass, since both its acceleration and the ...
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Does more rain strike a vehicle while moving or while stopped (or neither)? [duplicate]

Assume there is a rainstorm, and the rain falling over the entire subject area is perfectly, uniformly distributed. Now assume there are two identical cars in this area. One is standing still, and ...
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What is the origin of the naming convention for position functions?

In physics, position as a function of time is generally called $d(t)$ or $s(t)$. Using $d$ is pretty intuitive, however I haven't been able to figure out why "s" is used as well. Is it possibly based ...
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Relation between velocity and position vector in a central force

I am aware that the dot product of the position and velocity vector, $(\vec{r}\cdot\vec{v})$, in circular motion under a central force, $F(r)=-\frac{k}{r^2}$, is equal to zero as the two vectors are ...
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Difference b/w Kinetics & Kinematics w/concrete example

(I know whether I understand this or not doesn't matter much to my work & study but am just curious.) I still can't differentiate in my head kinetics and kinematics (similar thread is found but ...
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Intuitive explanation of the half in the $\frac{1}{2}at^2$ distance equation? [duplicate]

The full equation $$ Xf = X_o + V_o t + \frac{at^2}{2} $$ is integrated from the velocity function (which was integrated from constant acceleration function), right? The problem is, I can't seem to ...
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1answer
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Terminology for time derivative of speed (not velocity)

Is there any standard terminology for the derivative of the magnitude of velocity with respect to time (suitable for use in first-year Calculus)? The word ‘acceleration’, in its technical sense, is ...
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A question regarding 3-particle phase space for cross-section $2\to 3$

There is a book of Byckling and Kajantie, "Particle kinematics", discussing in particular (Chapter V) the kinematics of the $2\to 3$ cross-sections. It can be easily found in internet. I just want to ...
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Orbital velocity, orbital speed, tangential velocity

My mind is going around in circles over this. I know that orbital velocity is what a satellite requires to stay in orbit and I know what the equation is but I thought velocity was a vector not a ...
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In projectile motion, what does it mean for the motion along the $x$ and $y$ axis to be independent?

In projectile motion, what does it mean for the motion along the $x$ and $y$ axis to be independent? This question is referring to the concept of projectile motions.
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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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Utilizing maximum acceleration $a$ for displacement $d$ with initial velocity $v_0$ and final velocity $v_1$

Problem My goal is to move an object from point a to b (displacement $d$) as fast as possible utilizing the maximum available acceleration $a_{max}$, taking into account the initial velocity $v_0$ ...
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1answer
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Doppler effect formula when the medium is moving

We know the basic formula of apparent frequency in Doppler's effect. $f'=\frac{v_{sound}\pm v_{observer}}{v_{sound}\pm v_{source}}f$. What do we do when the medium itself is moving, say with a speed $...
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Where did the kinetic energy formula come from? [duplicate]

I was looking for a proof for it and all rely on the work-energy theorem. But the work energy theorem relies on the kinetic energy equation. Ergo circular logic. So where did it come from?
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In Uniform Circular Motion, why does the normal accelaration not change the magnitude of velocity?

According to pythagorean theorem V2 should be greater then V1.But why doesn't it happen?
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Getting position from an accelerometer on an Android phone

I know that integrating acceleration twice will give me position (acceleration-->velocity-->position) but how can I do all this when I all I have are a set of data points (ex: 1 second = some # m/s^2);...
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1answer
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How to calculate impulse force of body hitting water?

I'm calculating the force of a body hitting water from a high height. So far I've figured out the velocity at the time of collisions would be 40 m/s. The body is 78 kg. I seem to need the time it ...
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2answers
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Acceleration vector for an object moving in a elliptic trajectory

I am interested in deriving what the radial and tangential components of the acceleration vector should be for an object following an elliptical trajectory centered on the origin, in which the ...
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1answer
242 views

Two objects connected by a rigid rod, one of which follows a determined path

Consider an object that follows a determined path, with it's position given by $f(t)$, parameterized by time. Then consider a second object that is connected to the first by a rigid rod of length $l$, ...
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Can a collision of 2 objects result in one object having a higher velocity than either object had before they collided?

Assume I had 2 perfectly elastic billiards balls of the same size and mass, that can roll on an endless billiards table losing no kinetic energy to friction. Is there a set of 2 velocities v1 and ...
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Using acceleration to plot position

Sorry if this question is dumb, and I know is physics 101, but I'm not that good with physics. I'm writing an iPhone program that by collecting the acceleration data of the device tries to replicate ...
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Finding normal and tangential velocity and acceleration for motion along a 3D curve

Basically, I have a major problem on my hands. As part of an assignment, I have been given a set of 3D points, as well as the time between them, and nothing else, and I'm supposed to find the ...
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1answer
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Finding resultant and direction of resultant

In this question- A motorboat is racing towards the north at 25km/h and the water current in that region is 10km/hr in the direction of 60 degrees east of the south. Find the resultant velocity of ...
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1answer
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Non-commutative property of rotation

Addition of angles are non-commutative in three dimensions. Hence some other angular vector quantities like angular velocity, momentum become non-commutative. What is the physical significance of this ...
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1answer
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Angular velocity by velocities of 3 particles of the solid

Velocities of 3 particles of the solid, which don't lie on a single straight line, $V_1, V_2, V_3$ are given (as vector-functions). Radius-vectors $r_1, r_2$ from third particle to first and second ...
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4answers
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Inelastic Collision and Kinetic Energy

We see that our calculations always gives a loss of Kinetic energy in inelastic collisions while the net momentum of the system remains the same. Where does the lost energy go while there is no trace ...
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Projectile motion formulas

Assuming: The equations for the vertical and horizontal components of my initial velocity. Are: $v_{x,i} = v_i \cos\theta$ and $v_{y,i} = v_i \sin\theta$ And the displacement components are ...
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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 ...
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1answer
201 views

Circular motion - vectors [closed]

We are asked to show that, if $$\frac{{\rm d} \mathbf{r}}{{\rm d}t} = \mathbf{c}\times\mathbf{r},$$ where $\mathbf c$ is a constant vector, then the body moves in uniform circular motion. I have ...
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1answer
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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\...
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Stellar outflows in the Milky Way

There appears to be a lot of evidence that gas flows outward in Galaxies. I've been trying to parse through the available data and am unable to get a clear answer to this question: is there any ...
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2answers
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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 ...
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How to know when to divide what components and equate them in dynamics of circular motion?

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\...
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1answer
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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 ...
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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 ...

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