# 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 ...
33k views

### 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 ...
4k views

### 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 ...
757 views

### 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 ...
11k views

### 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 ...
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 ...
874 views

### 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 ...
2k views

### 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 ...
6k views

### 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 ...
13k views

### 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 ...
3k views

### 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 ...
340 views

### 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 ...
412 views

### 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 ...
327 views

### 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 $v_0$ ...
37 views