# Tagged Questions

The time rate of change of the position of an object

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### Why does a free-falling body experience no force despite accelerating?

Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum. From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational ...
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### How find/estimate Parasitic Area (CDA) in order to calculate V(L/D)max?

I am trying to calculate the speed which maximizes lift/drag for an aircraft. Using Carson's paper, it looks to me like the only unknown variable is "f", the parasitic area, which Carson describes as ...
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### How to calculate position of object that have linear and angular acceleration at the same time?

Let's imagine that we have a boat with two engines: main and rotary engine. Main engine gives boat acceleration $a$ m/s² up to constant linear speed $V$ m/s. When engine turns off, boat slows down ...
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### How to find Tangential/Radial/Angular Velocity for motion in any curve?

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 ...
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### What factors affect the velocity of an object moving down an inclined plane?

If you have a small toy car rolling down an wooden plank, what factors would increase or decrease the velocity of said car. In the experiment my team originally stated that adding mass to the car ...
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### special relativity question [closed]

How can I find the velocity of an object given the time elapsed of trip from the frame of reference of the object and the distance from the frame of reference of Earth.
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### The relationship between velocity and radius [closed]

I have learned that for an object moving in a circle, there must be an inward force acting upon it in order to cause its inward acceleration. This is sometimes referred to as the centripetal force. ...
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### Determining velocity and angular velocity after a collision between two 2D rectangles [closed]

Say I have two rectangles, which each have four vectors (which represent their vertices), a velocity, a mass, an angular velocity and a rotation (which is only used to simplify calculations as I don't ...
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### When Does Mass Matter? [closed]

I have been trying to wrap my head around this idea for a month or so, and I am not really sure how mass plays into the velocity of a moving body. I have not taken physics in a while, but one thing I ...
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### Equation for a falling body including terminal velocity

I'm making an app that times how long it takes a pebble to fall, then calculates the distance it fell. I noticed that the simple $f(t) = \frac{1}{2}gt^2$ was becoming increasingly inaccurate as the ...
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### Is the magnitude and direction of gravity on an object the same as the objects vertical velocity?

I need to make a diagram for an entry level college physics class. I need to show the magnitude and direction of gravity on a flying object and also show the magnitude and direction of the objects ...
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### Can rotational velocity be transformed into directional movement?

If I attach a weight to a string, and spin it, I notice that the faster I spin it, the more it pulls away from me. So, I imagine what would happen if I arranged a very large machine, designed so that ...
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### What do things move relative to?

When someone says that a spacecraft in otherwise empty space is traveling at a constant velocity of 10 km/h (for the sake of convenience) then what is the reference point for which this measurement ...
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### Why is speed defined as coordinate derivative over proper time rather than observer's time in STR?

In special theory of relativity, why is 4-velocity defined as: $$u^\mu = \frac{dx^\mu}{d\tau}$$ and not as $$u^\mu = \frac{dx^\mu}{dt}$$ where ${\tau}$ is proper-time and t is time in some ...
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### Functional derivative in Lagrangian field theory

The following functional derivative holds: \begin{align} \frac{\delta q(t)}{\delta q(t')} ~=~ \delta(t-t') \end{align} and \begin{align} \frac{\delta \dot{q}(t)}{\delta q(t')} ~=~ \delta'(t-t') \end{...
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### instantaneous velocity center

The instant center of rotation, also called the instantaneous velocity center is the point fixed to a body undergoing planar movement that has zero velocity at a particular instant of time. For ...
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### Calculate speed from accelerometer

I am trying to use my accelerometer on my mobile device (smart watch to be specific) to calculate a persons arm swing speed. The data returned from the accelerometer is in $m/s^2$. Since the ...
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### Why $F_\mu V^\mu=0$ in special relativity? [closed]

I'm trying to prove why $F_\mu V^\mu=0$. Where $F^\mu$ is the four force and $V^\mu$ is the four velocity. Can anyone help me?
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### What are the Radial, Tangential and Linear Velocities in this Context?

From the pictures below, it has been said that the tangential component (represented by the tangent at $B$) the linear velocity of a particle moving from $A$ to $B$ is $r \omega$, which is equal to ...
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### Velocity ; Acceleration [closed]

A ball was thrown vertically upwards with a speed of 3m/s. The ball reached a highest point before falling down to the ground. What is the acceleration of the ball at the highest point? A 0m/s2 B ...
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### Explain $\Delta x = v_0t + \tfrac{1}{2}gt^2$ please? [duplicate]

$g = \Delta v/t$, so $\Delta v = gt$. $v = v_0 + \Delta v$, so $v = v_0 + gt$. So if $\Delta x = vt$, then $\Delta x$ should be $v_0t + gt$. Why the $\tfrac{1}{2}gt^2$? I'm really confused, so this ...
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### Acceleration at rest when ball is thown [duplicate]

If a ball is thrown vertically upward and it comes to rest for a moment, then its velocity decreases and becomes zero. Does its acceleration also becomes zero? If yes then how ball falls down?
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### Small Animal Terminal Velocity

I recently saw a cat fall probably 100 feet like in this video Cat Falls. It seemed as if the cat reached terminal velocity by the time it hit. Does this mean that cats (and other small animals) could ...
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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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### Maximum velocity of a ball down a slope

I have the following situation: The dimensions of the ball are significantly smaller than the dimensions of the slope, and there is no friction. I'd like to know the maximum velocity of the ball ...
A 1d thin layer of a fluid of constant density in hydrostatic balance can be modeled by shallow-water equations: \begin{align*}\partial_tu+\partial_x\left(v+\frac{u^2}{2}\right)&=0,\\ \...