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7
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5answers
1k views

Earth moves how much under my feet when I jump?

If I'm standing at the equator, jump, and land 1 second later, the Earth does NOT move 1000mph (or .28 miles per second) relative to me, since my velocity while jumping is also 1000mph. However, ...
-1
votes
2answers
229 views

Simple Vector Problem [closed]

I'm a bit stuck on a homework question that I've been assigned. The question is as follows: You are paddling a canoe at a speed of 4 km/h directly across a river that flows at 3 km/h. (a) What is ...
1
vote
0answers
26 views

Rolling (without slipping) ball on a moving surface 2 [duplicate]

Possible Duplicate: Rolling (without slipping) ball on a moving surface Apparently I didn't log in properly when I asked a question this morning: Rolling (without slipping) ball on a moving ...
2
votes
1answer
490 views

Rolling (without slipping) ball on a moving surface

I've been looking at examples of a ball rolling without slipping down an inclined surface. What happens if the incline angle changes as the ball is rolling? More precisely I've been trying to find ...
13
votes
7answers
3k views

How can kinetic energy be proportional to the square of velocity, when velocity is relative?

Let's start with kinetic energy (from los Wikipedias) The kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a ...
1
vote
2answers
139 views

Moon and the moving train

While travelling by train (travelling West to East), it seems the moon is moving in opposite direction when seen from the window, but then it reverses its direction, after a certain amount of time and ...
1
vote
0answers
155 views

What direction a flag on an object moving in the wind shows?

"The flag of a ship that is moving northward with 10 km/h, points exactly southwestward. The windsock at the lighthouse points under 30 relative to the western direction southward. Calculate the ...
2
votes
1answer
220 views

Galilean relativity in projectile motion

Consider a reference frame $S^'$ moving in the initial direction of motion of a projectile launched at time, $t=0$. In the frame $S$ the projectile motion is: $$x=u(cos\theta)t$$ ...
2
votes
3answers
691 views

Riddle: can you swim faster upstream than downstream (with respect to the water)?

A friend of mine posed a riddle to me: A man swims upstream in a river, which is flowing at an unknown rate. He is wearing swimming goggles. At a certain point he loses his goggles. 10 minutes later ...
4
votes
5answers
744 views

Measure absolute speed

Currently I'm 17 years old, going to secondary school. So, my ideas might be totally wrong... I know that everything is relative. In the example of speed, the earth moves, and the galaxy moves, etc. ...
1
vote
1answer
84 views

Waves travelling with water flow

Suppose I use a tool to create a circular wave in the river. If there are two fish swimming 1m from the source (2m from one another), they will both feel the wave at the same time. What will happen ...
1
vote
1answer
733 views

Calculating velocities using Reference frames

Suppose an object A is traveling at a velocity of 100 m/s, and another object B is traveling at 105 m/s. With both the objects traveling through the same direction, taking A as a reference frame, the ...
0
votes
1answer
140 views

Galileo's dictum and how light cannot violate it

Okay. So I've been told that the speed of light is constant and cannot violate Galileo's dictum, but even if it weren't constant (in a vacuum), how would it violate it anyway? Say you are on a train ...
3
votes
5answers
322 views

Space Expansion vs. Relative Motion

Inspired by a recent dialogue from another question: Given 2 objects moving at some velocity $v$ relative to one another, is it possible to determine whether they are moving or whether the space ...
1
vote
1answer
354 views

Relative Speed vs speed of light [duplicate]

Possible Duplicate: Travelling faster than the speed of light Someting almost faster than light traveling on something else almost faster than light I've got two questions which are ...
0
votes
3answers
854 views

Does an airplane's speed include the speed of the Earth?

After take off, does airplane's speed include Earth's movement/speed? Do airplanes turn with Earth movement/rotation?
0
votes
1answer
246 views

Bee in a vehicle [duplicate]

Possible Duplicate: Speed of a fly inside a car Just a conceptual question: If a flying bee is inside a speeding vehicle, will it have to "fly" just as fast as the vehicle to stay aloft ...
7
votes
2answers
2k views

How to deduce the theorem of addition of velocities?

Lorentz contraction and time dilatation can be deduced without Lorentz transformation. Can you deduce also the theorem of addition of velocities $$w~=~\dfrac{u+v}{1+uv/c^2}$$ without Lorentz ...
0
votes
1answer
164 views

What would happen to electronic circuits when traveling near the speed of light?

Imagine a space ship, loaded with all sorts of computer systems, traveling near the speed of light. Electricity itself is very fast, and can reach speeds close the speed of light. (up to 99% ...
5
votes
3answers
1k views

Is acceleration relative?

A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. ...
0
votes
1answer
194 views

In What Frame of Reference does the Special Theory of Relativity Operate? [duplicate]

Possible Duplicate: Time Dilation - How does it know which Frame of Reference to age slower? This has bugged me for years. According to the theory of relativity, the faster an object ...
-1
votes
4answers
886 views

How does a train, airplane measure its speed?

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 ...
0
votes
2answers
1k views

What will be the relative speed of the fly? [duplicate]

It has happened many times and i have ignored it everytime. Yesterday it happened again . I was travelling in a train and saw a fly (insect) flying near my seat. Train was running at a speed of ...
5
votes
1answer
389 views

Lorentz force law in Newtonian relativity

I know that in special relativity Electric and Magnetic fields mix together in different reference frames, but my question is about classical mechanics. It seems weird to me is that the Lorentz Force ...
2
votes
3answers
713 views

Does being suspended in air allow you to not be affected by Earth's rotation?

Let's assume that there was some mechanism by which we could remain suspended in air. By this I mean that our feet is not in contact with the ground. One possible way of doing this would be by means ...
2
votes
1answer
378 views

Einstein Relative Motion and Time Order of Events

According to Einstein, do observers in relative motion agree on the time order of all events? I don't think they would agree on the timing of events, but I am having trouble figuring out why they ...
2
votes
4answers
506 views

How is this classical “paradox” resolved in electromagnetism?

A magnet and a coil move relative to each other. In the frame of reference of the magnet, there is a magnetic field and consequently a force acting on the charges in the coil according to the Lorentz ...
2
votes
2answers
598 views

Galilean transformation in relativity

Assume flat spacetime in a general relativistic framework (or special relativity for that matter) and two observers $A$ and $B$, with non-vanishing velocity relative to each other. We know that they ...
1
vote
5answers
8k views

Will a ball thrown straight up in a train land in same spot (in real world)?

I have a question that came up in a discussion with friends. If I throw a ball straight up in an enclosed train car moving with constant velocity, I believe the basic physics books say it will land ...
3
votes
1answer
192 views

Equation of Motion in a Non-Inertial (Rotating) Frame

Let me preface my question by informing you this is for an assignment, so I would rather not have explicit answers but rather be given guidance in arriving at the correct solution. The question is ...
2
votes
3answers
273 views

A question on Galilean Relativity

In a test I took recently in my beginning Physics class there was a question that really irked me: A man is swimming upstream at 10 mph. The water is flowing downstream at 5 mph. How fast is ...
6
votes
2answers
241 views

Why absoluteness of time implies galilean transformations?

In Landau course, vol.1 Mechanics, one finds the statement: ...the absoluteness of time necessarily implies that the ordinary law of composition of velocities is applicable to all phenomena. I ...
4
votes
6answers
4k views

How fast is Earth moving through the universe?

As the galaxy is moving and the solar system orbiting the galaxy and the Earth orbiting the sun. So how fast is each object moving and what is the fastest we move at? Do we even know how fast the ...
42
votes
8answers
17k views

Why does the atmosphere rotate along with the earth?

I was reading somewhere about a really cheap way of travelling: using balloons to get ourselves away from the surface of the earth. The idea held that because the earth rotates, we should be ...
2
votes
4answers
241 views

Chosing a reference frame in which the earth is at rest and doesn't rotate

We may choose a non-rotating earth as our reference frame and ask ourselves: how about the planetary and stellar motions. A star at a distance of 10 million light years would turn around the earth in ...