I was sitting in my brummer last night (motoring link) and I thought, "I wonder where that comet will appear in the sky . Then I was sent this by a friendly relative.
encke.jpl.nasa.gov/images/02C1/c2002c1chart.jpg
Anyone seen it yet? It may still be below the horizon here at 53 degrees North.
I also saw the Earth move! Looking at Venus, low in the West, I noticed some power lines in my line of vision. Venus was just above the upper cable. As I watched, it moved behind the cable then re-appeared below. Here we are, spinning at over 1000 mph.
BTW is it true that Mondeos are known for scrubbbing front tyres. I recall seeing it written somewhere. Looks like we are about to lose some very good Michelins on my wifes car. Outer edges are going, yet the tracking is said to be OK.
|
|
My old V6 Mondeo was a tad hard on front tyres.... or was that me?
|
|
|
Alwyn,
Wonder if you were star gazing at the same time as me ? I wasn't in my car but leaning on it to steady my binos. I may have seen one of NOAA's satellites of course !
Cheers Gwyn.
|
Gwyn,
I was mooching about all night trying to get a sight but as the Square of Pegasus is not yet above the horizon, I don't expect to see it until April.
Take care
|
|
|
|
Alwyn,
It's definitely below the horizon tonight - Comet Ikeya-Zhang - sounds like when you sit on one of their cheaper sofas!
As the night goes on, it'll get even lower - the best time to look will be just after dusk from early April.
If you are into this stuff, there's a great CD by DK called 'Redshift 4'.
I have never owned a Mondeo.
Martin.
|
|
|
|
I've had mine for 6 years from new. Wears its front tyres as true as a dye. Fronts last about 22k miles - never kerbed though.
|
|
|
Mini roundabouts do that to Mondeo front tyres.
HJ
|
|
|
Alwyn
Just to be pedantic, you are only spinning at 1,000 mph if you are on the equator.
It reduces with latitude to zero at the poles.
I am sure that Mark (Brazil) will have the formula, it's similar to the one he produced for the capacity of a drum!
Regards
Brian
|
Brian,
Point taken. As we are nearer the Pole than the equator at 53 degrees north, would you settle for say, 400mph ? Ish?
So while I am driving at 70 mph west, I suppose in reality, from another reference point, I am really going east at 330 mph? Makes you think. Well, it does me anyway.
Cheers
|
|
|
|
such confidence inspires me........
First some examples for easy comparison..
North Pole - ............0 km/hr..........0 MPH
42? N Latitude - .1300 km/hr.......806 MPH
Equator - ..........1670 km/hr.....1035 MPH
42? S Latitude -. 1300 km/hr.......806 MPH
South Pole -............0 km/hr..........0 MPH
And the exact formula with explanation...
newton.dep.anl.gov/askasci/env99/env057.htm>Difficult Spinning Stuff
|
That 42 degree speed is higher than intuition would suggest being almost the halfway point. So much for my intuition.
I remember the polar axis is 26 miles less that the equitorial, thus making the earth an oblate spheroid. Is it centrifugal force that causes this?
|
Alwyn
Yes, the Earth is actually an oblate spheroid. As Michael Caine one said 'Not a lot of people know that', and this time I reckon he's right!
Yes, I believe it's due to centrifugal force.
Back on topic, I had an Escort with a severe problem for wearing the outside edge of one front tyre. Ford dealer couldn't solve it, only had simple tracking gear, but an independent 4 wheel alignment system showed a significant misalignment of that one wheel.
Regards
john
|
|
|
|
Mark,
Beat me to it!
But that might be a good thing, as the last time I tried to explain something it came out as waffle and gobbledygook.
Martin.
|
PS
The fact that the earth is an oblate spheroid is caused by centripetal acceleration (a more accurate description that centrifugal force). (See what I mean?).
Martin.
|
Martin,
So what is the "conservation of angular velocity"?
Is this the effect where a beautiful girl in a tu-tu spins on her ice skates with her arms outstretched, and, as she brings them in, she speeds up?
|
Mark, read the first two lines of your post - didn't bother with the rest.
Velocity means speed and direction.
|
|
|
...Momentum...
Yes, she speeds up when she pull her arms in.
*Newtonian*
Steve Paterson - gawd, it's all so quickfire!
Martin.
|
|
Mark, I don't speak or read Spanish. To be honest, the Spanish proverb made as much sense to me as your description of velocity did.
|
|
|
|
|
|
|
Thanks for that Mark .Had my breakfast , off to calculate my cosine from my latitude in radians. Great start to the day.
B. Rgds Phil. I
|
|
|
Alwyn
Just think, in that case your car does 330 mph BACKWARDS ! :-)
|
|
|
indeed - or a "squashed sphere"
I believe the distortion is due to the momentum generated by the earth spining at high speed. The Centripetal force is what prevents the earth breaking up into millions of tiny pieces and spinning off into the universe at 1000 mph. (Or less ...)
|
What? a giant, multi legged bug is holding the world together?!?
Oh, that's a Centipeed...
What about Centrifugal force, I thought it was gravity that counreracted that to stop bits flying off...
John R
|
JR
Yes, gravity stops the loose bits flying off, but the rotation stresses the fabric of the earth, causing a small distortion.
Regards
john
|
Now don't get me started on Quantum Mechanics v. Relativity as that would be off topic...
Martin.
|
|
|
|
>>So while I am driving at 70 mph west, I suppose in reality, from another reference point, I am really going east at 330 mph? Makes you think. Well, it does me anyway.
No, much faster than that. Don't forget that not only does the earth spín, it orbits. And that which it orbits also moves as does that within which it orbits.
That car of yours is capable of untold thousands of miles an hour. Of course, with your luck there are also intergalactic speeding cameras.......
|
Mark
From memory, the orbital speed is 160,000 mph..
'ow did they measure that?
|
They measured it by......red-shift, displacement, speedometer?
Martin.
|
|
|
|
On the subject of speed cameras, one went off as I passed it on my way to work yesterday and another on the way home.
The first was due to the Roller, reg. K* 9, which was passing me at the time and the other due to a faster vehicle in the outdide lane of the North Circular.
What's the betting, that as I was on 'bike, I get the NIPs?
At the North Circular one I was doing 35 in a 50 limit. That was deliberate because there was a temporary 30 limit there until last week and the camera was reset to enforce that. I am not sure if they have reset it to 50 because it is going off very frequently now, whereas it never used to!
|
|
|
Brian,
Firstly we were talking about intergalactic speed cameras.
Secondly, don't they flash twice to photograph you moving over white dashes ? In which case, you wouldn't have moved enough surely ?
M.
|
|
|
Mark
Sorry, just for a moment I came back to Earth!
Reading your post again, I have just realised what Pulsars are, they are the camera flashes.
All we have to do now is work out where G*d put the cameras.
|
|
|
Alwyn,
I read a letter in yesterday's Daily Post. Was it yours (larsen B etc) ?I seemed to recognise the style (mind you the writer's name and location was a tiny clue)
hence the NOAA reference in my reply.
Gwyn
|
Gwyn
Yes, twas me. Someone else has mentioned my "style" of writing; she said "I knew it was you before I saw the name".
Shows how limited my edukayshun was.
They missed a little out of the letter. Tish.
|
|
|
|
Martin,
The falling ball on the train is always a good one.
Time is not constant, its relative. I just wish I could exploit that.
|
Mark,
So tell us why astronaut who has been astronauting comes back to Earth a little younger than he would have been had he stayed on Earth.
Or so I am told.
|
|
|
|
Akwyn,
users.commkey.net/Braeunig/space/basics.htm>Difficult Space flight Stuff
users.commkey.net/Braeunig/space/orbmech1.htm#moti...s>Difficult Orbital Stuff
musr.physics.ubc.ca/~jess/hr/skept/Grav/node11.html>Difficult Orbit Calculating Stuff
school.discovery.com/lessonplans/activities/animat...l>Difficult Orbit Simulation Stuff
The next is a really interesting page of space stuff...
www.newton.dep.anl.gov/askasci/astron98.htm> Difficult Astronomy Stuff
Study well, for questions will be asked...............
Kram.
|
|
|
Conservation of Angular Momentum
Momentum is the product of inertia and velocity. Inertia means the tendency of something not to change, and velocity means how fast it moves. So momentum means the tendency of an object in motion not to slow down. Momentum is of two kinds, angular and linear. Both kinds of momentum are conserved in any collision. Conservation means that none is lost, so the total momentum of the system before the collision, plus any additional impulse from outside the system, will equal the total momentum after the collision. This conservation principle is key to deriving formulas.
Angular momentum is the tendency of a rotating object to keep rotating at the same speed about the same axis of rotation. Angular momentum is measured with respect to a certain axis of rotation. The axis of rotation we will use is the axis at the middle of the hand, between the ring and middle fingers, perpendicular to the ground, and through the racquet handle.
By means of the conservation principle, it's possible to write a before and after equation for angular momenta about this axis of rotation. Here's how it works for a tennis racquet hitting a ball:
The racquet has a swingweight (moment of inertia, or rotational inertia, denoted by the symbol I). In rotation about the axis of rotation, the racquet also has an angular velocity (symbol w), measured in radians per second (a radian is about 1/6 of a full circle -- there are 2p radians in a full circle). Together, these variables define the racquet's angular momentum.
The angular momentum of the racquet, Iw, is its tendency to keep rotating about the axis of rotation despite the impact of the ball. Let's call the angular velocity of the racquet about the axis of rotation before the collision w1 and after the collision w2. The angular velocity of the racquet will slow down due to the collision, but racquet swingweight stays the same.
The angular momentum of the ball is a little more difficult to understand. It's not the spin of the ball in flight, but the angular momentum about the axis of rotation in the hand. The ball has a mass and a velocity, therefore it has a linear momentum. The impact point on the racquet will be a certain distance (d) from the axis of rotation. Angular momentum of the ball is the product of linear momentum times distance from the axis of rotation. So the angular momentum of the ball with respect to the axis of rotation is its mass (b) times its velocity (s) times the distance of the impact point from the axis of rotation (d).
We can, in this case, disregard external forces such as the force applied by the player's hand during impact when writing the equation describing conservation of angular momentum. This is an important assumption, so some argument is in order:
The line of action of all angular momenta is the same, the axis of rotation at the middle of the hand. And the line of action of any Impulse Reaction (push or pull of the player) passes through the axis of rotation, so this force, although impulsive, does not contribute to angular momentum. The external force we would like to disregard is the turning force, or torque, put in by the player during the impact. If it is a non-impulsive force, we can disregard it. This player torque is what has generated the racquet's angular velocity w1 right before the impact begins, and a few milliseconds more (0.004 seconds under our two Benchmark Conditions) of its operation will not materially change w. Any torque is the product of swingweight I and angular acceleration a about the axis of rotation, torque = Ia. Any actual change in the racquet's angular velocity w due to this torque will be small because the angular acceleration has such a short time to operate, so any additional angular angular momentum Iw will be negligibly small. The racquet head will not greatly change its position in 4 microseconds. The resultant Torque from impact, which acts to twist the racquet back, will be found later once the change (w1 - w2) in the racquet's angular velocity due to impact is found.
As noted before, the axis of rotation is between the ring and middle fingers of the hand holding the racquet. With respect to this axis, we can write an equation that is expressed in words like this:
angular momentum of racquet before collision (Iw1)
plus
angular momentum of ball before collision (bs1d)
equals
angular momentum of racquet after collision (Iw2)
plus
angular momentum of ball after collision (bs2d)
In symbolic shorthand: (Iw1) + (bs1d) = (Iw2) + (bs2d)
With algebra, we can get an expression for the difference in angular velocity before and after the collision:
(Iw1) + (bs1d) = (Iw2) + (bs2d)
(Iw1) - (Iw2) = (bs2d) - (bs1d)
(w1 - w2) = (bd/I)(s2 - s1)
This angular velocity difference is key to finding a formula for Torque, Shock, Work, and Shoulder Pull. The ball velocities and the distance of the impact point from the axis of rotation are set by the Benchmark Condition, but the formulas are generalized so that any ball speed and any impact point may be used.
|
|
|
Alwyn,
You really need to read these excerpts and the full book.
www.generationterrorists.com/quotes/abhotswh.html>REALLY Difficult Stephen Hawking Stuff
However, I still don't see how this is going to help you beat speed cameras ??
Mark.
|
|
|
>>Mark, read the first two lines of your post - didn't bother with the rest.
I am inconsolable. It is intrinsic to my enjoyment of the very fabric of my existence that one Steve Paterson should read each and every line of my posts.
There is no way forward. There is no longer purpose in life for me.
I am bereft.
Or, as they say in an ancient and very well known Spanish proverb "ponga su cabeza encima del parte posterior de un oso que sea muerto"
|
|
|
Pay attention Steve, I was describing momentum, not velocity.
Didn't you know they were different ?
|
|
|
Did you ever get a good answer to the tyre question? I never noted one and, as a Mondeo driver of over 100,000 miles (what WAS I thinking...?) haven't really noticed bad wear. Suppose you could discount the front near side inner edge worn to sticking out cords and having Kw** **t track me (it WAS Sunday) the front offside wore the same....(left side for toe-in, right for toe-out). Recently had a 4 wheel track done...time will tell.
Haven't noticed the comet yet. Thought they were actually turned into the Nimrod, mainly used in search and rescue......OK...OK....I will look in my garden tonight and check for the damned thing. Will I stand a chance, being right on the East coast...?
|
|
|
