The time rate of change of the position of an object

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4
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4answers
787 views

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 ...
1
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1answer
39 views

Displacement of an object due to opposite and equal forces acting at different times?

This question is about mechanical waves in solids, the speed at which forces propagate through solids, and the displacement that might occur due to unequal starting times of equally sized forces. ...
0
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1answer
372 views

Distinguish between instantaneous speed and instantaneous velocity

I encountered a line in my text book of physics that: Average speed over a finite interval of time is greater or equal to the magnitude of the average velocity. But instantaneous speed at an ...
11
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2answers
2k views

How fast would a spaceship have to go to reach Alpha Centauri within a person's lifetime?

Given the recent news about the discovery of an "Earthlike" planet orbiting Alpha Centauri (our nearest stellar neighbour) it got me wondering just how fast would spaceship have to travel to be able ...
1
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3answers
136 views

Does this count as moving faster than light?

I'm not familiar with any complicated physics equation, however I do understand some basics. Suppose there is two objects, both of them are moving away from each other in a 3-dimensional space, which ...
4
votes
3answers
376 views

Is speed an intensive property?

I remember being taught in elementary physics that while it makes sense to add volumes, masses, or heat, it makes no sense to add temperatures. As I wanted to use that to illustate some other issue, ...
2
votes
1answer
24 views

Eddy Currents: Relationships between thickness and deceleration

This is probably a question with a very simple answer, but I want to make sure before I write too much. I'm doing an investigation on Electromagnetic fields, in particular eddy currents and how they ...
4
votes
1answer
2k views

Terminal velocity of two equally shaped/sized objects with different weights?

I've tried doing research on this and there are some similar questions. However, they have slightly different scenarios and to make sure I understand things perfectly, I wanted to word it into my ...
-2
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0answers
28 views

Negative friction [closed]

A 1kg wood cube. This cube is affected by friction i reverse. Instead of decelerating it will accelerate at an equal rate. Placed in the middle of a concrete room where it has 0.63 coefficient ...
2
votes
1answer
125 views

Does decreasing the length of the line between a harness and zip wire increase the velocity at which you travel?

My friend is an instructor at an outdoor adventure centre which has lots of zip wires. The instructor's harness has a shorter line that attaches to the zip wire than the normal harness does and she ...
1
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0answers
51 views

Is Gravity related to velocity? [closed]

Is the missing link of what creates gravity, the velocity that an object rotates or moves through space ? Can a small object with little mass which rotates or moves in enormous speed create a strong ...
-2
votes
1answer
46 views

If we could reach very high speeds, could we measure the velocity of the Earth this way?

If we could reach (nearly) the speed of light with spaceships, could we measure the velocity of the Earth by launching three perpendicular rockets, accelerating them, and measuring how much fuel ...
1
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1answer
59 views

Special relativity: circumventing velocity-addition formula

Two spaceships approach an observer from an equal distance and from an opposite direction with an equal speed $v$ in the observer's intertial reference frame $O$. The speed of a spaceship in the ...
0
votes
1answer
74 views

Is there any significance to the negative sign on this speed?

A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$) If the ...
5
votes
3answers
194 views

Is it faster underwater to go down without air or up with air?

So I had a very interesting conversation between me and my friends about this topic, but we could not find the answer. The Situation Lets say you are in a pool and you want to touch the bottom and ...
1
vote
1answer
15 views

Knock out drum sizing for 10 times velocity reduction

How can I size a drum such that the velocity is reduced by 10 times inside the vessel. My velocity in the pipe entering the drum is 9.77 m/s. Velocity inside the drum should be 10 times less than 9.77 ...
1
vote
1answer
72 views

What is the airspeed velocity of an unladen swallow? [closed]

I got asked this question for my physics course at college, i'm not the best at airspeed velocities... What is the airspeed velocity of an unladen swallow? I still can't find anything to help ...
0
votes
1answer
50 views

Calculating force of a car [closed]

I'm simulating car cruise system and my results are not making any sense. I have been told that my force formula is wrong but I don’t understand why it is wrong and how I can fix this. Does anybody ...
1
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3answers
36 views

How to approximate acceleration from a trajectory's coordinates?

If I only know $x$- and $y$- coordinates of every point on a trajectory without knowledge of time information, is there any way to approximate Cartesian acceleration angle at each point? Time interval ...
0
votes
1answer
330 views

Deriving the group velocity of a wave produced by some basic cosine waves with unequal amplitudes

Consider some basic cosine waves of the form ${E_i} = {E_0}\cos ({\omega _i}t - {k_i}z)$ with different amplitudes, frequencies and phases. We know a combination of such waves could result in a wave ...
2
votes
2answers
201 views

What is the terminal velocity of a sheep?

Inspired by this question on Gaming.SE Using actual in-real-life physics, what would the terminal velocity of a sheep actually be? I would assume it would be around 50m/s, but I might be wrong. ...
1
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1answer
21 views

Swinging onto a Hill

I was just watching the movie "Frozen" (not the Disney one), and they were trapped in a ski lift 50 feet off the ground. They had to jump. My question is, when they jump, should they swing on the ...
0
votes
3answers
1k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
0
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0answers
12 views

What is the linear and rotational motions generated by a force not on the CG?

Given a force that is applied to a free body, not directly towards, or away from the centre of gravity, how would you calculate the amount of linear and rotational velocities generated, as the farther ...
1
vote
1answer
73 views

What is the speed of light from a star moving towards a observer.? [duplicate]

We can say that in vacuum speed of light is constant. But if the star is moving with a certain velocity does it add that velocity to the velocity of photons emitted out of that star?
1
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1answer
803 views

Sound velocity in water

Conductivity, temperature, depth sensors are used by oceanography to calculate the velocity of sound at varying depths. These measurment values are used to comprise sound velocity profiles like the ...
7
votes
5answers
3k views

How long must escape velocity be maintained?

Escape velocity from Earth's surface is 11.2 Kilometres/second How long would one need to maintain this escape velocity to actually escape Earth's gravitational pull? Must this 11.2 km/s velocity ...
0
votes
4answers
66 views

If the velocity vector of a moving particle is always perpendicular to the position vector, is the path a circle?

A Newtonian physics question: If the velocity vector of a moving particle is always perpendicular to the position vector, is the only possible path a circle? What if the magnitude of the velocity ...
1
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1answer
59 views

Can speed be defined in the complex plane?

This question cropped up while I was playing with the equation for time dilation. If I set the speed to be $i$ (imaginary unit) the answer from the equation still makes sense, but does that matter if ...
0
votes
1answer
73 views

Does speed in space really matter?

This is about validating the science from a science fiction novel. My understanding is that speed is all relative. So while I am in a car on the freeway my speed relative to another passenger is ...
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0answers
109 views

Is there any place you can safely skydive without a parachute?

While trying to explain to someone how a kitten walked away from a fall from a skyscraper I got to wondering if there's any place a human could do that and I find myself out of my depth. The only ...
4
votes
2answers
3k views

How can an object's instantaneous speed be zero and it's instantaneous acceleration be nonzero?

I'm studying for my upcoming physics course and ran across this concept - I'd love an explanation.
1
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2answers
42 views

Help explain how direction change relates to acceleration [duplicate]

I was doing some simple harmonic motion problems and I came across this picture describing the position, velocity and acceleration of a linear oscillator. At the moment in time when v is 0 the ...
0
votes
1answer
66 views

Determining fluid flow velocity from experimental volumetric flow rate data

I would be very grateful if someone helps me with my issue. I have a pump pumping water into a tube. My goal is to find velocity of the fluid flow in another tube that will be connected to the first ...
0
votes
1answer
27 views

Difference between short impact and sustained pressure

If I press the wall (with my hand) I feel a little pressure at my hand and I move away from it. If I hit the wall (lets say using the same amount of energy for total work) I feel pain in my hand. ...
2
votes
1answer
103 views

How to find equation of motion for this trajectory? - object leaves curved ramp at a given velocity [closed]

Here is the sketch: The sketch is supposed to be side-view of the path of the object. The following values are known: $r$ - radius of the circle that describes the path AB of the object $a$ - ...
1
vote
1answer
38 views

Why is work not related to velocity?

A very simple question; why does it cost me more energy to very slowly lift a mass $m$ over my head compared to very fast? The definition of work does not state anything about velocity, only the ...
0
votes
0answers
28 views

How to calculate the equation of projectile motion for curved ramps? [duplicate]

Consider the following cases (these are sections): I can find the equation of motion for Case a however I don't know how to deal with Case d. Normally I would need the angle α otherwise I can't ...
18
votes
1answer
496 views

What determines the speed of waves in water?

While I was walking my dog this morning, I passed over a canal filled with boats, barges, and kayaks all of different masses and moving at different speeds. I noticed that all of these vessels left ...
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4answers
143 views

Experiment - Measuring final velocity of a parachute

I'm working on a project that involves a scale parachute. It is vital for the project to get a good measurement of the speed it has when it lands. We still haven't built the parachute, but we need a ...
2
votes
2answers
189 views

How do you travel in a circular orbit around a massive body?

I am trying to figure out how an object could achieve a perfectly circular orbit. Given a mass for the planet or other body the object is orbiting and a distance from the center of mass, how fast ...
0
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2answers
42 views

Finding out the velocity [closed]

Displacement of an object is related to time $x=at+bt^2-ct^3$ where a, b and c are constant motion.Then the velocity of an object when it's acceleration is zero is given by ...
0
votes
1answer
42 views

Question regarding FTL information transfer between two inertial frames

Why can’t information travel faster than the speed of light, if the two endpoints to and from which the information is being sent are moving relatively to each other, as long as the information ...
0
votes
3answers
45 views

Kinematics - Concept of average velocity

Average velocity, as I have heard, cannot be found simply by finding the average of two numbers. I have a question on average velocity, but am simply unable to proceed: A particle moving in a ...
3
votes
4answers
507 views

Deriving $F = ma$ - Newton's Second Law of Motion

Context: In my textbook it is given: 'momentum' short for 'linear momentum': Mass = $m$, momentum is $p=mv$. In time $\Delta t$, momentum changes by $\Delta p$, the rate of change of momentum is: ...
1
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1answer
57 views

Constant speed in curved space

Suppose a spaceship is travelling in the Schwarzschild metric. An observer at infinity sees the spaceship moving at constant velocity. What does this mean? Does it mean that: \begin{align*} ...
0
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1answer
38 views

Velocity at certain point?

I seem to have misunderstood something in velocity. There is a path from point A to point B, that gap between is 100 meters. An object moves from point A to B with a velocity is 10 m/s. ...
2
votes
0answers
42 views

Physical Interpretation of four velocity in GR

I'm confused about the physical interpretation of the four-velocity $U^\mu=\frac{dx^\mu}{d\tau}$ in General Relativity. I know that it is a tangent vector to a particle's "worldline", but what does ...
1
vote
1answer
49 views

Travel time for accelerating object [closed]

I have an object which starts at velocity = 0. Accelerates to a known max speed and continues thereon at constant velocity (max speed). My problem: How long does it take to reach a known ...
1
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1answer
21 views

Speed distribution in 1 dimension

In 3D, the maxwell velocity distribution is: $$f = \left(\frac{\alpha}{\pi} \right)^{\frac{3}{2}} e^{-\alpha v^2} d^3 \vec v$$ To get the speed distribution in 3D, we simply expand $d^3\vec v = 4\pi ...