Scalar quantity which is the magnitude of velocity.

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5answers
284 views

What is the slowest possible speed?

According to special relativity, nothing can go faster than the speed of light, and nothing can be distinguished to be in a state of absolute rest. So it makes me wonder: is there a slowest ...
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1answer
29 views

Find the average speed and velocity of the object [closed]

An object travels 11 m north and then turns around and travels 25 m south. If the total time of travel is 52 s what is the average speed and velocity of the object. I used the formula I was told ...
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1answer
45 views

Top speed for a human

What is the fastest that a human being of average weight could possibly travel, and what is the most widely held theory for how this might be achieved (assuming this person is impervious to all forms ...
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0answers
13 views

speed of sound and ultrasound machine

How can you determine the speed of sound of a liquid using a medical ultrasound probe? I am unable to get a hold of a hydrophone. Is it possible to determine C using a or m mode?
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1answer
279 views

How can I calculate the speed of an object knowing its horizontal and vertical velocity components?

Let's say a ball is thrown and it experiences typical projectile motion (moves in a parabolic arc etc.) and the only information we know are the equations for the horizontal and vertical components of ...
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2answers
74 views

What is the fastest speed that a massive object can travel at? [duplicate]

What is the fastest speed (in miles per hour) that a massive object can travel at? I have heard that an object can travel at the speed of light, but I've also heard that massive objects cannot travel ...
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0answers
51 views

Why do motors have a speed limit? [duplicate]

The force which will move a body with this motor will be the difference between the force of the motor say 2N and the resistance - friction force - say 1N then the sum of forces will always be ...
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2answers
76 views

Time dilation due to change in speed

I can't get something strait... Lets use the usual example: A man is flying away from earth on a very fast spaceship. So, His time is now not moving in the same "speed" like earth time but slower. But ...
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2answers
69 views

Why is most probable speed not equal to rms speed for an ideal gas?

The rms speed of ideal gas is $$\mathit{v_{rms}} = \sqrt{\dfrac{3RT}{M}}.$$ The most probable speed is the speed where $\dfrac{dP(\mathit {v})}{dv} =0$ where $P(\mathit{v})$ is the probability ...
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2answers
94 views

Light wave crossing media and the relationship between speed, wavelength, and frequency

There are many threads on this topic (like this one) but one aspect about the equation $ v = \lambda\nu $ still confuses me. I have read that frequency does not change when light crosses into ...
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1answer
31 views

At what velocity would a body need to travel at to experience noticeable (couple minutes) time distortion?

When a person experiences higher speeds, the light must travel a greater distance to reach the person whom is moving compared to that whom is staying still. Right? So therefore, light takes slightly ...
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2answers
2k views

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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1answer
249 views

How fast do molecules move in objects?

I guess it depends on the heat or the type of the material but can you give some examples or formulas to calculate it ? The best example would be the average speed of the air molecules (all types in ...
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1answer
82 views

If a car moves at a certain speed, how fast is its wheel going?

Say in a given instance a car moves with speed $v$ and consider any wheel of the car. How fast is it going? Is it the case that the center of the wheel moves at the same speed as the car i.e. $v$? Why ...
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1answer
57 views

Problem related in relative motion [closed]

The speed of a boat is 1.5 m/s in still water. One needs to cross a river of width 500 m with this boat. Along the direction of the river a strong wind is blowing with a speed of 0.9 m/s. The boat is ...
0
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2answers
142 views

Speed of electrons in resistors

What affects the speed of electrons in a resistor? If two resistors are connected in series, they both have the same current; same number of electrons passing at a point per second. Suppose one ...
2
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1answer
3k 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 : ...
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2answers
3k views

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 ...
1
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0answers
112 views

One dimensional motion problem [closed]

I kept almost 2 hours trying to solve this problem : Two trains are 150 km apart. Train A moves at 50.0 km/hr towards train B, which moves at 30.0 km/hr toward train A on the same track. How ...
3
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1answer
194 views

How fast would an object have to move to create a vacuum behind it?

When an object moves, I assume that the air above it, instead of remaining at the same general height, is pulled downward as it is passed in order to fill the low-pressure area behind the object where ...
5
votes
2answers
396 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. ...
3
votes
2answers
256 views

Steel rod to Mars vs the speed of sound, how is supersonic travel possible?

I remember reading this passage in the "Feynman Lectures", where Dr. Feynman describes an experiment in which a theoretical metal rod of length equal to the distance between Mars and Earth is arranged ...
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4answers
1k views

What is our estimated running speed on Moon's surface?

I was wondering if we have the chance to run on the Moon's surface, how would you expect it look like? I expect our velocity will increase for the same work we do on Earth, but not sure if this will ...
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1answer
197 views

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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1answer
83 views

Why seeing further in “timespace” does not add up?

I've read that astronomers have received a light (a photon) 13 billion years old. Here's my question: If we start to turn the clock backwards all matter, energy, etc should start heading to the ...
3
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1answer
37 views

Can the speed of a vehicle be determined based upon the extent of injuries to a pedestrian?

While driving at night in a Prius, at varying speeds of 5-20 MPH in heavy, stop-and-go traffic on a 4 lane city street, two pedestrians in dark clothing were struck (not in a crosswalk). One died of ...
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9answers
3k views

What is the speed of the fastest moving body in our solar system?

On Wikipedia I saw that the average orbital speed of planet Earth around the Sun is a whopping $29 783\text{ m/s}$, and it made me wonder are there bodies (planets, meteorites, asteroids) that move ...
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3answers
613 views

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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1answer
123 views

From where we can view earth moving?

Earth moves with a speed around $100000 \,\,km/h$, which will be amazing, but from where we can see that moving speed? If we far away from earth (outside of earth gravity) then can view its moving? is ...
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3answers
4k views

Does an Increase of Force affect the Speed of an object if the acceleration stays constant?

If I had a mass of $100\:\rm{kg}$ accelerating due to gravity, using $F=ma$: $F = 100\:\rm{kg} \times 9.8\:\rm{m/s^2}$ $F = 980 \:\rm N$... If I increased the mass to 200kg, the force would be 1960 ...
4
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1answer
586 views

How does a particle of light reach the max speed of light? [duplicate]

Possible Duplicate: How can a photon have no mass and still travel at the speed of light? First of all I am not a professional physicist. I was curious as to how a particle of light can ...
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1answer
91 views

Analytical Mechanics [closed]

This is one of my three homeworks. I see that $W_a(1) = \dot U_a(1)=\ddot{X_a}(1) = 0.3 $ Since $U_{O'}=0 $ then O' is Instant centre of rotation. Then $U_b = 2U_a = 0.6$ I tried a lot, about a ...
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1answer
139 views

What does a speedometer measure?

When speaking of the velocity of a particle, we must specify a reference point. The same holds when we talk about the speed of a particle (is this correct?). If so, a speedometer measures instaneous ...
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2answers
2k views

Speed of a fly inside a car

A couple of weeks ago I was travelling in a car (120 km/h approximately) and I saw a fly flying in front of me (inside the car, near my nose, windows closed). I wonder how was that possible. Does it ...
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2answers
551 views

Why does time slow down when traveling at high speeds [duplicate]

One of the effects of traveling at high speeds is slowing down of clocks. I can understand gravity time dilation effect but not how would velocity affect clock speeds. How correct it is, if I say ...
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0answers
37 views

How to determine speed/energy of something dropped from a given height?

Say I dropped a ball from some height, which is measurable, is it possible to determine the speed of the ball when it hits the ground and thus the force exerted on the ball my the ground (or vice ...
2
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0answers
55 views

What does it look when we travel at the speed of light? [closed]

Suppose we're in a spaceship or in a car which runs at the speed of light. We are watching the light which is coming towards eyes at the speed of the light. What would it look like when the driver ...
4
votes
5answers
1k views

Force required to drive car

From what I know of Newtonian Mechanics, if an object is moving at a constant velocity, the net force acting on that object is equal to zero. If there is friction, then the applied force required to ...
14
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5answers
5k views

How fast would someone have to run to travel vertically up a wall?

I am currently doing a physics project on the effects of so-called 'super-speed'. I was wondering how fast you would have to run to vertically travel up a wall? That is, to negate the force of ...
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1answer
81 views

Rotating metal sphere

My knowledge of physics is not that great, but I am always willing to learn. I have the following question: If we have a sphere made out of metal with a radius of 1 meter, and it rotates in an ...
3
votes
4answers
3k views

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 ...
2
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0answers
53 views

Force and Energy in robots

There are two similar and hypothetical robots that move with wheels powered by motors, Robot A and Robot B. Robot A has a gear ratio of 3:1 (The gear connected to the motor is three times larger than ...
1
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1answer
258 views

how does air pressure affect the speed of sound

How does air pressure affect the speed of sound in relation to its kinetic theory etc? I have tried searching this but i have not found a suitable answer as other websites simply related to air ...
0
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1answer
113 views

If we could not see, would we think that nothing can go faster than sound?

And if so, then why does everybody keep asserting nothing can go faster than light speed (I'm implicitly assuming there could be something which we do not observe, which goes faster than light)?
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8answers
1k views

How to know if a vehicle is moving without any external source of information?

The situation is the following: I'm inside a vehicle (plane or a car, it doesn't matter) and I need to know if the vehicle is moving at a constant speed BUT I cannot perceive any external change like ...
1
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2answers
130 views

What is the speed of an electric spark/arc in vacuum?

I am just curious about the nature of an electric spark, how fast are the electrons moving? Will these electrons slow down when the spark occurs through a dielectric? (e.g., air)
17
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4answers
3k views

Why is there a controversy on whether mass increases with speed?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed. I understand how some (though not many) things in physics are a matter of ...
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2answers
189 views

What causes an increase in sound speed in a medium?

Its an established fact that increase in the temperature causes increase in speed of sound waves but what is the property which is changed by changing temperature ? Does frequency and wavelength get ...
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6answers
3k views

Why does the speed of light $c$ have the value it does?

Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed ...
2
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1answer
59 views

General equation of a wave

My book says that functions which represent a wave motions satisfy the differential equation : $$ \frac{\partial^2 y} {\partial^2t} = v^2 \frac{\partial^2 y} {\partial^2x} $$ where $v$ is the ...