# Tagged Questions

Scalar quantity which is the magnitude of velocity.

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### If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?

Of course aerodynamics factors into this question, and the faster you are moving the more air you have to push out of your way, the more energy you use. But would the difference be only a small ...
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### Speed of an object in air versus in vacuum

Okay, imagine that you are shooting a rocket down a tunnel that is 60 miles long and the rocket is travelling at 60mph, so the rocket should reach the end of the tunnel in a hour, right? Yep, in an ...
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### comparing torque and 0-60 speed in cars

Im looking a two cars, both are the same model but ones got a 2.0L turbo petrol engine and ones got a 3.0L turbo diesel engine. These are the full specs 2.0L Petrol 3.0L Diesel what im ...
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### Weightlessness on Earth

Would the following work? Imagine one would 1) create a straight 4000 km long tube (at ground level), following the curvature of the Earth, wide enough to hold a pod the size of an aircraft cabin; ...
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### Where to find the current positions and velocities of the planets?

I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in ...
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### Would an object hit the ground faster when it gets launched vertically upwards or downwards?

A while ago I had a discussion with someone about the speed of an object when it hits the ground. When does an object hit the ground faster: When you launch the object to the sky so it can fall down;...
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### How can I calculate the wave propagation speed in a copper wire?

First of all: I am a computer science student, so I don't have much knowledge of physics. So please keep your answers simple. I recently learned something about circuit design and its problems (...
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I am exploring the idea of measuring the humidity of a space using sound waves, however I am having trouble finding a mathematical relationship between the speed of sound and the humidity level. $c_{... 2answers 133 views ### super-jump air balloon [closed] We have the following objects: a 80 kg person a rope of negligible weight a balloon filled with helium, which can lift for around the same weight, 80kg. My question is, which of the following ... 3answers 21k views ### Why does an object with higher speed gain more (relativistic) mass? [duplicate] Today, in my high school physics class, we had an introductory class on electromagnetism. My teacher explained at some point that an object with a very high speed (he said it started to get somewhat ... 3answers 10k views ### Is the same amount of electricity used for ceiling and table fans on different speeds? We use ceiling and table fans in home which are can be set to low or high speeds using regulators. I want to ask that does it uses or consumes same amount of electricity at different speeds? Here, "... 2answers 366 views ### Speed of Entropy change If time in systems moving with different speed goes differently, does speed of entropy change differ in these systems? (is "speed of entropy change" a valid term? can we compare them?) 1answer 414 views ### Does$\lambda\nu = c$hold for all the waves in the universe? Are all waves in the universe the same as electromagnetic waves? Basically, my question arises from an equation I found in my chemistry textbook: $$\lambda \nu ~=~ c.$$ This states that the ... 2answers 1k views ### Is it possible to travel at precisely the speed of sound? I've been talking to a friend, and he said that it's impossible to travel at exactly the same speed as the speed of sound is. He argued that it's only possible to break through the sound barrier using ... 2answers 2k views ### Why does the wheel of a car appear to be moving in opposite direction? When a car is about to stop, the speed of its wheel reduces. Why do we see or feel that the wheel of the car is moving in the opposite direction? This can also be observed of a fan at home. So why ... 4answers 4k views ### How Felix Baumgartner has reached the speed of sound quickly I have watched Felix Baumgartner freefall; but I wonder how Felix has reached the speed of sound quickly, in a matter of some seconds, then we had no idea of its speed? Any explanation please. 5answers 5k views ### Why would a fat skydiver fall first in free fall? I was having one of those obnoxious conversations with a friend where he was arguing that a fat skydiver would reach the ground faster than a skinny skydiver. To me it seemed as obvious that the world ... 1answer 796 views ### Which speed can an electric scooter reach on a given slope? Electric scooters are always "given" as "working with slopes up to xx%", but what does it mean? Given motor torque and power, scooter+driver weight and wheels diameter, how can I determine at which ... 1answer 17k views ### How fast would someone have to run to run over water? I was thinking about Flash, the superhero, or the little boy in the Incredibles. There is one Yahoo answer that doesn't answer a lot. Especially, I don't think surface tension would help a lot for a ... 1answer 156 views ### What is the quantity in physics that is advanced from speed? [closed] What is the quantity in physics that is advance from speed? i know one is velocity, one is speed, one is acceleration. 3answers 3k views ### How will you measure speed in km/hr in space? How is the speed of an object in space measured? Also more importantly how do you measure your own speed in space? On the road we use a speedometer which tells us the speed easily. How is it done in ... 2answers 5k views ### Can human hand move at a speed rate like this baseball pitch or is it just the speed of ball? Fastest baseball pitch ever recorded was in 1974 at a speed of 100.9 miles per hour. Does this mean that the pitcher's hand was also traveling at that speed or just the ball? Is it physically ... 1answer 294 views ### Something almost faster than light traveling on something else almost faster than light [duplicate] Possible Duplicate: Travelling faster than the speed of light Double light speed Lets say that an airplane can fly at 4/5 of the speed of light, and I can run at 2/5 of the speed of light, ... 3answers 912 views ### Finding instantaneous speed in MPH given acceleration, RPM and gear ratio I am still trying to figure out how to (semi) accurately model instantaneous speed after having found acceleration. I have found that at higher RPMs, the resultant acceleration will be lower. I was ... 3answers 2k views ### How to determine an exponential acceleration curve? I've always been not so bad in mathematics, but I'm terribly bad at physics. For me, abstract concept are totally understandable, but when it come to reality, I'm lost ! So, for my job, I need to ... 3answers 8k views ### Does friction decrease as objects move faster against each other? I was told that the faster two objects move against each other, the less the friction between them would be… compared to if they were moving slower. So does friction decrease when the body is moving ... 2answers 48k views ### How exactly does mass affect speed? I konw that mass affects weight (force), so how does that relate to speed? F=ma. so how does all this affect speed? 1answer 4k views ### Which derivation of drift velocity is correct? In the derivation of drift velocity I have seen two variations and want to know which one's correct.$s=ut+\frac{at^2}{2}$Assume that the drift velocity of any electron in any conductor is : $$\vec{... 1answer 3k views ### The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures? The speed cannot increase unboundedly of course, so what happens? 1answer 107 views ### A Satellite's Perspective If a planet is spinning east to west and there is a satellite spinning from west to east... Can the satellite travel at a speed sufficient to make the planet appear, from the vantage point of the ... 1answer 6k views ### How does one derive the equation for the speed of sound? In my acoustics books I see$$c^2 = \frac{\mathrm{d}P}{\mathrm{d}\rho}$$where$c$is the speed of sound,$P$is the pressure and$\rho$is the density. Where does this equation come from? In my ... 2answers 550 views ### Laws of aerodynamics after breaking the sound barrier my knowledge of physics is not very extensive, so I hope my question isn't too stupid. I know that when (for instance) a plane breaks trough the sound barrier, the laws of the aerodynamics change. ... 1answer 357 views ### How to calculate the dependency of speed and weight of a servo? [closed] Here is a digital servo: Servo By using the information of details of that thing what is the way to calculate the dependency of the speed of the movement of the car if the load upon the servo is N kg ... 4answers 2k views ### How does a train, airplane measure its speed? [closed] I always get the doubt about this. I know that a bike measures its speed based on the motion of its front wheel. So what is the case with train? Is it same principle? Then what about an airplane? Is ... 1answer 918 views ### Local Mach number for an airfoil I would like to know how to calculate the local Mach number on the upper surface of an airfoil given the ambient temperature, the local velocity on the airfoil surface, the freestream velocity, and ... 1answer 321 views ### Approximate Time Dilation at Rocket Speeds How do you calculate the time dilation effect experienced by a traveler traveling at a relatively low speed? Specifically, how much time dilation would a traveller moving at$v=0.0007 c$(speed of ... 2answers 3k views ### Sign of Velocity for a Falling Object I'm working on a homework problem in Mathematica. We have to graph the height and the velocity of a function given an initial height and initial velocity. However, when I do the graph for the velocity ... 1answer 492 views ### Angular velocity$\omega$by$v$We have two girls, with mass ($M$). They become close to each other in speed of$V$. The distance between them is$3L$. I was asked to calculate the Angular velocity ($\omega\$) of the two girls. So ...
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This stems from a riddle I read in a magazine perhaps 20 years ago so I apologise for the imprecise recollection. A dog that can run infinitely fast is placed on an infinitely large flat surface and ...
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### Speed of Light, Photons or WaveSpeed?

The speed of light is almost 300 000 km/s. The photons have a speed along the wave, and the wave have a speed straight forwards. What is the speed of light? Is it the speed the photons have along ...
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### How does electricity propagate in a conductor?

On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity. And I've read that the net electron drift is slow. But electricity ...
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### Speed of a particle in quantum mechanics: phase velocity vs. group velocity

Given that one usually defines two different velocities for a wave, these being the phase velocity and the group velocity, I was asking their meaning for the associated particle in quantum mechanics. ...
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### speed of light flashlights question

This might be a silly question but I take the risk because it's been puzzling me for quite some time : If you have 2 flashlights, one facing North and one facing South, how fast are the photons (or ...
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### How dangerous is firing a bullet straight up in to the air? [closed]

Question's title says it all how dangerous are the bullets which are fired up straight in to the air? I often find myself in this discussion where there are people who argues that it is harmless and ...
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### How fast gravity force propagates? [duplicate]

Possible Duplicate: The speed of gravity Lets say for example that a pertubance occured on the Sun that changes its distance to the Earth. How fast we are going to notice the gravity changes? ...
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### Fuel usage at the same constant rpm at different gears

I've had a discussion with my father today, about the fuel usage of a vehicle at the same rpm, but a different gear. He claims that the following situations have the same fuel usage: ...
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### Terminal speed of a body in a gravitational free fall? [closed]

What speed would a small body moving towards a large body reach under gravity alone? More importantly, is there a 'terminal speed' for the small body due to the increasing energy required to ...
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### Ascent rate and size of balloon

I am part of a school project, Project Stratos to send a balloon to the edge of space (the closer side :P) and was wondering how you would work out the accent rate of a large balloon (roughly 1m^3 of ...