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Questions tagged [speed]

Scalar quantity which is the magnitude of velocity.

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What is the drift velocity of an electron in a superconductor?

How is it,when compared to drift velocity in a conductor?
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Relationship between speed and power in wind/hurricanes

I was looking at hurricanes today when question crossed my mind. Cat 1 Hurricanes are the ones going up to 95mph. Cat 5 goes above 157 mph. That says a lot, but not all. In motors or engines, RPM ...
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92 views

What determines the direction of a photon emitted by an electron?

When an electron loses energy and emits a photon, what determines the direction that this newly-created photon will travel? The electron, being a point entity, has no internal physical structure, so I'...
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53 views

Speed of sound in a gas and speed of a typical gas molecule

Why is speed of sound in a gas less than the average velocity of the gas molecules? Is there an intuitive way to explain this?
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2answers
113 views

If an object moves at constant speed, does it necessarily have constant velocity? [closed]

If an object moves at constant speed, does it necessarily have constant velocity?
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If two bodies move constantly but with different speed, do they move with acceleration relative to each other? [closed]

If two bodies move constantly but with different speed, do they move with acceleration relative to each other?
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Is there an agreed upon physics definition of the term 'speed'?--for example, can it be negative?

The term speed is commonly defined as follows: https://www.physicsclassroom.com/class/1DKin/Lesson-1/Scalars-and-Vectors Speed, being a scalar quantity, is the rate at which an object covers ...
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Why isn't average speed defined as the magnitude of average velocity?

Speed is usually defined as the magnitude of (instantaneous) velocity. So one could assume that average speed would be defined as the magnitude of average velocity. But instead it is defined as $$s_{...
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What is the maximum speed of waves in stagnant water?

I want to learn the maximum speed conditions for a wave in a fluid. I think, Which mechanism causes this limited speed? And How? The water is an understandable example for me. By this question, I ...
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36 views

Calculating the Instantaneous speed

When we are calculating speed from the graph for a uniform motion the speed which get as an answer is actually the average speed and since in uniform motion the average speed is same as that of ...
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2answers
32 views

What is the speed of rotation of the magnetic field of a solenoid or current-carrying WIRE

How does one find the speed of rotation of the magnetic field around a current-carrying wire? or How fast is it circulating around the wire? How does one identify the speed of rotation of the ...
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1answer
54 views

How to calculate the radius of a curve based on vehicle wheel speeds of a car

I have data of the 4 differen wheelspeeds of a vehicle during driving time. Based on that I want to calculate the radius of a curve it is taking. The following are my current thoughts that seem to be ...
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Speed of sound for a given frequency in a non-ideal gas (humid, room temperature air)?

I'm trying to understand what the speed of sound might be like for a given frequency in non-ideal and non-dry air. Wikipedia states that speed of sound has a weak dependence on frequency in ordinary ...
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39 views

Speed of two objects orbiting around a central axis

This question has been bugging me for quite some time and i'm not too sure if i'm missing out some important factor in the understanding of this scenario: Given two objects of equal mass and size ...
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1answer
81 views

Can acceleration be both the “rate of increase of velocity” and the “rate of increase of speed” in Physics?

A Dictionary of Physics (Oxford University Press) defines acceleration as: The rate of increase of speed or velocity However, from reading many other definitions it seems to me that acceleration ...
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1answer
65 views

How to find the speed of a single photon?

Firstly with the help of $E= hf$ I calculated the energy by taking the frequency of light as $6 \times 10^{14}\ \rm Hz$(the range of frequency of light is from $4$ to $8\times10^{14}\ \rm Hz$ so I ...
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Relation between The speed and Temperature of the molecule

I'm fully aware of Gay-Lussacs Law, but when I was reading Feynman Lectures on Physics volume 1, sir said that the temperature and the speed of the gas (Ideal Gas) are proportional to each other. But ...
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2answers
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How instantaneous speed is defined as magnitude of instant velocity? [closed]

Let $s=$distance (a variable) we define instantaneous speed = magnitude $\left[\frac{ds}{dt}\right]$. However instantaneous speed is also defined as magnitude of instantaneous velocity i.e. ...
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Speed of the Accelerating Expansion of the Universe [duplicate]

So I heard that the universe is exponentially expanding faster than light, but I heard it just expands 72 km/s per megaparsec, I am not sure what is what, if someone can give me a logical or ...
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1answer
38 views

Do blades on the same rotor really move at different speeds?

I was browsing Stack (great way to kill time at work) and I came across this question. One of the comments confuses me somewhat. @Zlelik No, helicopter blades cannot exceed the speed of sound - ...
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1answer
277 views

Why does sound travel faster in steel than in water?

I understand that sound travels faster in water then in air. Water is a liquid, and air is gas. Water still has the ability to roll the molecules over each other (so water can flow), it has some ...
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1answer
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Einstein $E=mc^2$ equation what if we found an element energy? [closed]

I started research in time travel idea soon and iam asking what if there exist an element that gives energy equals to c^2 in the equation is the mass of this element is 1 ( i don't know the unit ...
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4answers
82 views

How can we calculate the speed from $E=mc^2$? [closed]

how can we calculate the speed of an object using the formula of Einstein $E=mc^2$?
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1answer
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Wheel size for climbing up on inclined surface

I am going to make a Line follower robot which can climb up on a inclined bridge(45 degree with flat surface). If speed remains constant, Should I use bigger wheel to enable the robot to climb easily? ...
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2answers
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Increasing speed of a car using more motors? [closed]

I am making a robot car with four wheels. Every wheel will be attached to a motor. If I use four motors and four wheels , will I get more speed then using two motors?(If all the motors rotate at same ...
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2answers
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Does the density of water affect the speed of sea waves?

In the case of light waves, the denser the matter, the more slowly they propagate. Do the water waves behave identically?
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1answer
49 views

Why does sound wave travel faster in solid medium than in fluid medium? [closed]

Sound is a mechanical wave, it propagates due to vibration of particles. Does density of medium affect the speed of sound through it? In air speed of sound increases when density of air decreases. ...
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1answer
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cancelling the speed of a moving object [closed]

Hi I can't seem to get this thought out of my head. Is the light from a moving object begin from a zero position. If for a brief instant the object were to stop would that cause the negation of the ...
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1answer
77 views

Speed, velocity, and momentum of light

As far as I understand speed is a rate of travel and velocity is a directional rate of travel. The equation for momentum is given as follows $$p=mv$$ Where $m$ is mass and $v$ is velocity. Case 1. ...
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2answers
69 views

What happen if a body travel with fast speed?

Suppose a car is moving with high speed ( say 100km/hr ) Now, while moving with such speed is the mass of car going to change with respect to car at rest?
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2answers
31 views

Speed of Medium Compared to Wave Speed

Do the particles in a medium oscillate about their equilibrium position at the same speed as the wave moves through the medium? Is it the same for both transverse and longitudinal waves?
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2answers
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Can speed vary within a given interval of uniform motion in a straight line?

The definition of 'Uniform motion' in a straight line says that the body covering equal distances in equal intervals of time is to be understood to be in uniform motion. However, can the speed vary ...
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2answers
132 views

Why is light speed the only constant speed?

I've been thinking about special relativity and I did the following math (I’m a beginner in this relativity so sorry if the problem I did has mistakes) Let’s suppose a spaceship travelling at $\frac{...
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1answer
27 views

Adding momentum to pulling force

A winch is pulling a 90kg object in any direction but it is limited in potential speed by its torque. Would a burst of momentum by perhaps a coiled spring or jet propulsion pushing the object towards ...
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Orbital speed change when closer to the sun

So a thought had passed my mind recently and i was wondering if an object like mercury has a greater orbital speed than the earth. Yes, i am aware that distance makes a difference but i talking about ...
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4answers
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How do I find the instantaneous velocity in real life? [closed]

I am learning about Instantaneous speed and velocity in Khan Academy. I understand the concept and calculation, but how do I know the different instantaneous speed at different points in real life?
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How is this formula of the speed of sound derived?

$$c^2 = \frac{n}{m} \frac{\partial^2 U}{\partial n^2}$$ where $U$ = vacuum energy density as a function of the quasiparticle density $n$ = quasiparticle number density $m$ = bare mass of ...
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3answers
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Velocity of Sound of Air Being Negative?

Recently, I have learned that the velocity of sound in air is increased or decreased by temperatures, assumed from the formula V = 331 + 0.6 x (TC), TC being the temperature in Celsius. Then, I ...
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1answer
114 views

How long could someone survive in free fall? [closed]

If there was hypothetically a bottomless pit (no ground), then approximately how far down could you possibly survive without being killed by the speed? (there is no vacuum so air resistance matters.)
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How fast does an object's weight change?

So, the title is a bit odd, I know. But I am curious, if you placed a stick that was 1 lightyear long on a scale (Yes, we are assuming that the whole stick is experiencing the same gravity as the ...
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Speed of electrons in a current-carrying metallic wire: does it even make sense?

Does it make sense to speak about the speed of electrons in a current-carrying wire (non perfect conductor)? If so, what is their speed? Here are my thoughts: On the Internet (Wikipedia, ...
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1answer
40 views

How to calculate new speed using newtons second law based on previous speed

I am creating a train simulator game, and I want to calculate the new speed based on previous speed. I know i can calculate speed in my game with speed=(f/m)frames elapsedseconds per frame But If the ...
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3answers
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Is current the speed of the electrons?

My teacher got me really confused this time. He said that current is the rate of flow of charge. If this is true, then current could be the speed of the flow of charge (ie. the kinetic energy of the ...
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2answers
155 views

Question about Speed of Sound

I'm looking over PowerPoint slides of my past Physics lecture and I'm confused about a point my professor made: The speed of sound is much higher in a liquid or a solid. It turns out that the speed ...
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If a satellite performs an reentry, how does its speed vary?

If a satellite were to leave the Earth's orbit and perform a reentry with no parachutes or rockets to slow it down, how does its speed vary? I know that from equations, as orbital radius decreases, ...
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5answers
301 views

What's wrong with this argument that kinetic energy goes as $v$ rather than $v^2$? [duplicate]

Trying to non-technically explain why (kinetic) energy goes as $v^2$ rather then the perhaps-more-intuitive "double the speed, double the energy" $v$, I ended up putting my foot in my mouth (itself a ...
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4answers
63 views

Is possible to use the air friction to increase the speed of a car?

Its possible to make a device that, attached to the car, it will use the air that hits the car at high speed and give the car a boost?
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1answer
31 views

Different time for same amount of kph/mph change at different speeds

First of all excuse me if my english isn't perfect, and if the question is hard to understand, even I am a little confused about what do I even want to ask. So I bought a new wristwatch not too long ...
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Compute angular velocity from 2 linear velocities

How do you calculate the angular velocity of an object (in my case a robot) where you input the linear speeds for each of the 2 wheels (independently)? I'm not sure what to look for in my searches, ...
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0answers
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How does the speed of an object affect its relativistic mass? [duplicate]

I am reading the book A brief history of time by Sir. Stephen Hawking and at chapter 2, Space and Time, the author discussed about how the speed of an object affects its relativistic mass based on ...