# Tagged Questions

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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### Which came first, movement or heat?

According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket ...
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### Rigid body dynamics joints

I can't seem to find any info on connected rigid bodies by a joint. Can someone explain the basics to me? I'm trying to do a little research to find out how feasible it would be to implement 3d ...
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### Help me get out of a speeding ticket

I was driving uphill from a complete stop for a distance of .4 miles estimated to take 1 minute in a navigation app. I was pulled over right after cresting the hill. The cop had me on radar going ...
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### How can there be really any instantaneous velocity?

I have read about Zeno's arrow paradox that tells us there is no motion of the arrow at a particular instant of its flight. It can be inferred that there can be no velocity at any instant. Moreover we ...
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### Intuitive answer to a kinematic problem

The problem: Two particles A and B start from rest and move for equal time on a straight line. The particle A has an acceleration a for the first half of the total time and 2a for the second half. ...
532 views

### Dodging paintballs

I was recently watching The Matrix, and was considering the speed at which one needs to move to literally dodge a projectile. Now, in real life, it is impossible to dodge bullets as such a feat would ...
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### Does an object move because it has Kinetic Energy or does it have Kinetic Energy because it is moving?

Maybe to explain I'm wondering if an object gains $\rm K.E.$ which causes it to have a velocity or does an object have a velocity which cause it to get $\rm K.E.$?
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### Can velocity be an undefined quantity?

We have the image below displaying the uniform velocity by time-distance graph. At every point velocity is constant but what if distance and time both become zero as at origin in the graph is? The ...
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### How can an object move from point A to point B?

If I was at point $A$ and I wanted to walk directly to point $B$, I would have to walk half way to point $B$, but before that I would have to walk half way to halfway to halfway to point $B$ and half ...
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### What causes a car's velocity to follow the front wheels' direction?

I'm trying to simulate a car with correct physics models. In this example we let the car have a constant speed, and there are no forces (friction and drag) to slow down the speed. Here's a video that ...
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### Free falling objects

My teacher and I are in the middle of an argument because she says that if you were to drop two objects at the same time and the same height, but with different initial velocities, both of them would ...
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### Proof of centripetal acceleration formula ($a_c = v^2/r$) for non-uniform circular motion

The formula for centripetal (radial) acceleration is well known, and there exist many proofs for it: $$||a_c|| = \frac{||v||^2}{r}$$ However, all the proofs I've seen rely on the fact that it is ...
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### How much does it cost every time your car stops for a traffic light?

Every time we have to stop the car, it is costing us extra money, because we have to then accelerate to full speed again. I would like to know how much. In order to simplify the situation, we can ...
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### Two vehicles moving in a line with different accelerations

Let two similar vehicles starting at rest in a straight line (with a distance of $D$ between them) have time-varying accelerations in the same direction. If both of them have similar time varying ...
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### Maximum range of a projectile launched from elevation “dumbed down”

I am trying to conceptually understand why the angle which produces the greatest range for a projectile launched with an elevation is not 45 degrees. I have exausted all other options, and I hope that ...
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### Ion Drive Propulsion Top Speed

I would like to know if there is some formula / graph which would provide / show the efficiency of a certain type of propeller in space. Specifically, I'm interested in the acceleration attainable at ...
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### Calculating Kryptonian speed in the movie “Man of Steel”

This is my first question, so I'm not sure if this is the right place to ask but: How would you go about calculating the speed of Kryptonians in the movie Man of Steel (2013)? Specifically, I'm ...
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### How to calculate a collision which is partly elastic and partly inelastic?

(For the purpose of this question, "calculating a collision" means: given the velocities and masses of two objects in a collision, figuring out the new velocities of both objects after the collision). ...
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### Area under a displacement graph

If the area under an acceleration-time graph denotes velocity and the area under a velocity-time graph denotes displacement, what exactly does the area under a displacement-time graph denote?
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### The Double Integrator: Matching velocity and position as quickly as possible with only a limited amount of force available

If a body with mass $m$ begins at position $x_0$ with velocity $v_0$ and experiences a force that varies as a function of time $f(t)$ (and we ignore gravity, friction, and everything else that might ...
242 views

### Is it possible to rotate an angle on perfectly smooth ice?

You must start and end with the same pose. Prove it if you think you can't.
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### Object docking in Space

How do objects dock in space? There's a recent piece of news that Keppler would dock to the ISS sometime this week. I want to know the operational aspects of it - considering the velocity of the ...
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 ...
### $v^2 = 2ax$ or $v^2 = ax$?
As far as I am aware, $v^2 = 2ax$ is the formula to find the velocity in various questions. If kinetic energy = work, $$\frac{1}{2}mv^2=Fx$$ $$mv^2=2max$$ $$v^2=2ax$$ We use this formula to solve ...