Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum Am I Moving?

Wrong, the top of the plane is not moving with respect to the ground. It it was the plane would move from its position on the runway.

Not necessarily. If there is a tail wind the air speed may be less than the ground speed.


This is probably just a minor error. Angular momentum is measured in degrees per second, or whatever units you using. The linear velocity of the inside and outside of the record will be different, but not the angular velocity.

Bill Gill

It's obvious that you are wrong Bill.



no it wouldnt Bill.

the wheels of the plane that are in contact with the ground are moving at the same speed as the ground.



I think you have that backwards Bill.

a tail wind would cause the aircraft to have a greater air speed , ( speed it up )
a head wind would cause the aircraft to have a lesser air speed ( slow it down )

in a tailwind mechanical instruments would show a lesser air speed
( because there is less air pressure acting on the speed sensor / measuring device )

but the actual air speed
( of the aircraft )
would increase.


http://en.wikipedia.org/wiki/Tailwind





No error

Bill , you need to refresh your studies.

http://en.wikipedia.org/wiki/Angular_velocity



as in the above the angular velocity of the top of the plane
is greater than the angular velocity of the ground.

also as above the angular displacement of the top of the plane is greater than the angular displacement of the ground.

its pretty simple to figure out.

I cant understand why you guys are having such a difficult time with it.

Paul, while your plane is on the runway, with its wheels stationary, climb on to the top of the plane, stick the end of a length of string to the top - use your chewing gum if you like - now come down and stick the other end to the ground, vertically below the chewing gum. If the top of the plane is moving relative to the ground your string will not remain vertical for long, and the plane will distort. Ergo, the top of the plane is stationary relative to the ground.

Similarly, in the case of the record; of course the outer edge is moving faster than the inner, relative to the surroundings, which for the sake of illustration, can be taken to be stationary; but any point on the outside of the record never changes its position relative to any other part of the record. That in my understanding is what constitutes being stationary relative to something.

A tail wind would cause the plane to have greater speed relative to the ground below, but would decrease its airspeed - i.e. its speed relative to the air through which it is flying.

Paul, Bill S. has pretty much pointed it out, but I will go just one step further.

Assume an arc 1 foot from the origin that subtends 30 degrees. Now draw an arc 100 feet from the origin that subtends 30 degrees. I agree that the 100 foot arc will be much larger than the 1 foot arc. But they both are 30 degree arcs. If you move something along the 1 foot arc in 1 second its angular velocity will be 30 degrees per second. Now move something along the 100 foot arc in 1 second. Its angular velocity will be 30 degrees per second. Obviously the object on the 100 foot arc will be moving much faster than the one on the 1 foot arc, in order to move 30 degrees in 1 second. There is a large speed difference between 2 arcs. There will be no difference in the angular velocity.

Bill Gill

your 100% wrong Bill.

you left out the most important part in your arc analogy.

( the lenghts of the two arcs)

it was tricky and underhanded , but something I have
become used to in this want to be science forum.

but suppose you do draw a 30 degree arc at a 1 foot radius from the center.
and you draw a 30 degree arc 100 ft from the center.

do you actually think that the arc at the 100 ft radius
will be the same length as the arc at the 1 ft radius?

LOL

not a chance...

the circumference of the entire circle at the 1 ft radius
point is 6.28 ft
the circumference of the entire circle at the 100 ft radius
point is 628.00 ft

and since you have used 1 second time for travel in both arcs
and since you have used 30 degree arcs , quite naturally you would have 2 travel times of 1 second both traveling
along a 30 degree arc.

you just left out the distance of the 2 30 degree arcs.

the 30 degree arc at a radius of 1 ft is 0.52 ft in length.

the 30 degree arc at a radius of 100 ft is 52 ft in length.

you say theres no difference in angular velocity
I say that there is , and plenty of it.

0.52 ft/sec angular velocity.
vs
52 ft/sec angular velocity.

so the difference in the two velocities is
a whopping 51.48 ft/sec.

If the forum is that bad, and the posters are "tricky and underhanded", how come you are the second most prolific poster ever?

Let me guess; you're trying to put things right.

You may need some help there, one perfect poster does not make a discussion forum.

the top of the plane is 50 ft higher than the ground.
it is moving faster than the ground.

you even agree in the below.



and the top of the plane is like the outer edge.

your talking about IAS indicated air speed.

the actual aircraft speed is what I was talking about.

and the actual air speed would increase in a tailwind.

and I think I covered the guages and pressures already
in my reply.




I wasnt talking about IAS indicated air speed , because I
was talking about the actual aircraft speed in a tailwind.



try and find a situation where actual air speed is less than ground speed without flying through a hole in the earth.

as long as the aircraft is flying above the ground its air speed will always be greater than its ground speed.

even if it is flying straight down.
or straight up.

theres no way around it.

second?

so who is the first?

No, Look up air speed in a dictionary.
Websters:
"Air Speed: The speed of an aircraft with respect to the air"

If you are going to use terms that have defined meanings you have to use them correctly. Since air speed is the speed of the air craft with respect to the air, then air speed is different from ground speed.

In regard to the angular velocity discussion I specifically said that the object moving along the 100 foot arc would move much farther and much faster than the object moving along the 1 foot arc. You completely ignored that part of my discussion and apparently wanted people to forget that I had made an accurate statement.

And lets look at what Webster has to say about Angular Velocity.

Webster: "Angular velocity - A vector quantity describing rotational motion, the magnitude of which is the time rate of change of angle and and the direction of which is along the axis of rotation"

You see, angular velocity has to do with a change in angle, not a change in distance. A 30 degree per second angular velocity is the same no matter if you are 1 foot from the center or 1 mile.

Bill Gill

Im going to clarify this for you bill.



hows that?



so you agree that the top of the plane would move faster than the ground.

something moving much farther and much faster must be moving
faster , right?

but you want us to think that the velocities would be the same if you moved something along both arcs in 1 second.
in other words the velocities are the same in both arcs.



let me do one of those bill

suppose I point my finger straight up.
then I swing my finger 45 degrees.
I do that in 1 second.
now suppose that there is a planet 1 trillion miles from
the center of the 45 degree point that my finger swings on.

and the planet swings with my finger the 45 degrees
in 1 second.

both have followed a 45 degree arc in 1 second.

so there is no difference in the two angular velocities.

no , the facts are that the tip of my finger
has a angular velocity of 2 inches / sec
the planet has a angular velocity of
785,398,163,397. miles/sec


http://en.wikipedia.org/wiki/Angular_velocity






angular velocity = angular displacement / time

following a thread that includes calculations that you dont understand can be a difficult task , so I've decided to put
my method of determining the distance / displacement of
a arc at a given radius.


suppose we need to determine the distance of a 30 degree arc
at a 1 ft radius.

radius x 2 = diameter
diameter x pi = circumfernce
circumference / 360 degrees = displacement / length / distance of each degree of the circumference.

this gives us the displacement of each degree in the arc.

each degree x arc degree = displacement of arc

r x 2 = 2
2 x 3.14 = 6.28
6.28 / 360 = 0.0174

0.0174 x 30 = 0.522 ft

the displacement of a 30 degree arc at a radius of 1 ft is
0.522 ft

if the distance along the 30 degree arc is traveled in 1 second then the angular velocity would be 0.522 ft/sec

Gentle readers: Here once again we see Paul refusing to recognize that he is wrong and trying to provide proof that everybody else is wrong. He is doing this by denying the common definitions of every day matters and substituting his own definitions. Please observe that this way he can prove anything, even when it doesn't match experimental proof.

Bill Gill

Paul, you can, of course, establish that anyone has said almost anything if you select your quotes with sufficient care.



However, the whole quote does say something different.

DA Morgan. 4136 posts in under three years!

This statement has no real scientific meaning unless you specify what the movement is relative to.

If any part of the plane were moving relative to the ground, the plane would not be stationary relative to the ground.

Can we agree on that?

All of that's true isn't it.

A point on the plane 50' higher than a point on the ground would, in 24 hrs, describe a circumference around the Earth 314' greater than that of the point on the ground. The plane and the ground beneath it remain in the same relative locations. In other words, the given point on the plane travels through local space faster (by 314' per day).

Agreed. This is fine as long as you accept Newton's "absolute space"; otherwise it makes no sense to talk of something moving relative to space.

http://en.wikipedia.org/wiki/Motion_(physics)



the top of the plane has changed its position 314 ft
more than the ground in a 24 hour period.

right redd!

observation of motion requires more



but if no one is there to observe the motion of an object
it still has motion.

I used 4000 miles as the radius of the outer edge of the ground and I used 50 ft as the height of the plane.

I dont need any frame of reference.

I already know that the earth rotates 1 revolution per day and that time period is 24 hours.

so I already know the angular velocity of the ground where the plane is sitting , all thats left is to calculate the greater
angular velocity of the top of the plane.

pretty simple stuff there guys.

and I hold that the top of the plane is moving faster than
the ground...