Undertaking....

[911hope]

Graveworm said:

911hope said:

Pica-Pica said:

911hope said:

snuffy said:

For the 180/360 degree agreement of ending up back where you started from:

Surely it's 360 degrees if your car moves round in a circle, but its 180 degrees if your car pivots around its central point?

If you do a u turn around a roundabout, you have not gone round a full circle.

Not this old discussion!

It is amazing that it is impossible that this cannot be resolved, but there are no tools to get through to people who don't have a basic understanding of maths.

https://math.stackexchange.com/questions/260096/find-the-coordinates-of-a-point-on-a-circle

Not sure what point you are making by posting this link, but it does not really relate to the rotation of an object approaching and following a portion of a circle.


Here are some basic concepts to chew on.

Car approaches roundabout and goes straight on... approximates to a square for simplicity...turns 90 degres left to enter the bottom edge, 90 right to head up the left hand edge, right 90to enter the top edge, left 90 to leave. Total of all direction changes is 0 degrees. Rotation of car between entry and exit is 0 degrees.


Now let's do the whole u-turn thing. define right turn a positive rotation. and left turn a negative rotation.

Start by heading UP

Enter the bottom edge -90
turn up left edge +90
turn across top edge +90
turn down right edge +90
turn across bottom edge +90
Leave to head down -90

Accumulated rotation is 180 degrees.

Car is facing opposite direction to initial path, so 180 degree rotation. (obviously). Notice how these 2 methods agree!

That is a U turn. 180 degrees that is answer.

If a car travelled tangentially (90 degrees to the radius) a full lap of a circle, it will have an accumulated rotation of 360 and will be facing the same way at the beginning and end of the lap. You will notice that this is NOT a U-TURN

This is where all the confusion comes from.

Hope this clears things up, but expect people will not accept it.

[Graveworm]

911hope said:

Graveworm said:

911hope said:

Pica-Pica said:

911hope said:

snuffy said:

For the 180/360 degree agreement of ending up back where you started from:

Surely it's 360 degrees if your car moves round in a circle, but its 180 degrees if your car pivots around its central point?

If you do a u turn around a roundabout, you have not gone round a full circle.

Not this old discussion!

It is amazing that it is impossible that this cannot be resolved, but there are no tools to get through to people who don't have a basic understanding of maths.

https://math.stackexchange.com/questions/260096/find-the-coordinates-of-a-point-on-a-circle

Not sure what point you are making by posting this link, but it does not really relate to the rotation of an object approaching and following a portion of a circle.


Here are some basic concepts to chew on.

Car approaches roundabout and goes straight on... approximates to a square for simplicity...turns 90 degres left to enter the bottom edge, 90 right to head up the left hand edge, right 90to enter the top edge, left 90 to leave. Total of all direction changes is 0 degrees. Rotation of car between entry and exit is 0 degrees.


Now let's do the whole u-turn thing. define right turn a positive rotation. and left turn a negative rotation.

Start by heading UP

Enter the bottom edge -90
turn up left edge +90
turn across top edge +90
turn down right edge +90
turn across bottom edge +90
Leave to head down -90

Accumulated rotation is 180 degrees.

Car is facing opposite direction to initial path, so 180 degree rotation. (obviously). Notice how these 2 methods agree!

That is a U turn. 180 degrees that is answer.

If a car travelled tangentially (90 degrees to the radius) a full lap of a circle, it will have an accumulated rotation of 360 and will be facing the same way at the beginning and end of the lap. You will notice that this is NOT a U-TURN

This is where all the confusion comes from.

Hope this clears things up, but expect people will not accept it.

There is no confusion - you keep describing the direction the car is facing or which direction it is driving after it has negotiated the roundabout.

Which is completely different to and seperate from what was being discussed, how to describe rotations around and position on a circle.

The earth goes once around the sun in an earth year. During that time it spins roughly 365 times about its axis. All the other planets are spinning and orbiting at vastly different rates, none of them follow a perfect circle but all of them complete 360 degrees for each full orbit back to their point of origin. They never leave the orbit but still they orbit.

180 degrees per second is 30 rpm. If you were correct it would be 60.

[911hope]

Graveworm said:

There is no confusion - you keep describing the direction the car is facing or which direction it is driving after it has negotiated the roundabout.

Which is completely different to and seperate from what was being discussed, how to describe rotations around and position on a circle.

The earth goes once around the sun in an earth year. During that time it spins roughly 365 times about its axis. All the other planets are spinning and orbiting at vastly different rates, none of them follow a perfect circle but all of them complete 360 degrees for each full orbit back to their point of origin. They never leave the orbit but still they orbit.

180 degrees per second is 30 rpm. If you were correct it would be 60.

Try to understand that a U-turn on a roundabout is not a full orbit. Any analysis based on this comparison is therefore flawed.

A planetary orbit will have the satellite getting back to the same point after one lap and moving in the same direction. This is fundamentally different to the U-turn.

If you can't see this, then think of it this way.

A U-turn in a road would be 180 degrees, surely you would admit that.

This is physically equivalent to a U-turn on a mini roundabout, which is equivalent to a big roundabout.

[Graveworm]

911hope said:

Graveworm said:

There is no confusion - you keep describing the direction the car is facing or which direction it is driving after it has negotiated the roundabout.

Which is completely different to and seperate from what was being discussed, how to describe rotations around and position on a circle.

The earth goes once around the sun in an earth year. During that time it spins roughly 365 times about its axis. All the other planets are spinning and orbiting at vastly different rates, none of them follow a perfect circle but all of them complete 360 degrees for each full orbit back to their point of origin. They never leave the orbit but still they orbit.

180 degrees per second is 30 rpm. If you were correct it would be 60.

Try to understand that a U-turn on a roundabout is not a full orbit. Any analysis based on this comparison is therefore flawed.

A planetary orbit will have the satellite getting back to the same point after one lap and moving in the same direction. This is fundamentally different to the U-turn.

If you can't see this, then think of it this way.

A U-turn in a road would be 180 degrees, surely you would admit that.

This is physically equivalent to a U-turn on a mini roundabout, which is equivalent to a big roundabout.

Yes a U turn in a road would be 180 degrees FOR the car. If it drove around the block seven times to get there you wouldn't say that was the same as if it spun on it's axis like a fork lift. You are replacing what was being talked about, orbiting a roundabout with a false equivalency. You can drive 12 miles and end up in the same place you still drove 12 miles.

[911hope]

Graveworm said:

911hope said:

Graveworm said:

There is no confusion - you keep describing the direction the car is facing or which direction it is driving after it has negotiated the roundabout.

Which is completely different to and seperate from what was being discussed, how to describe rotations around and position on a circle.

The earth goes once around the sun in an earth year. During that time it spins roughly 365 times about its axis. All the other planets are spinning and orbiting at vastly different rates, none of them follow a perfect circle but all of them complete 360 degrees for each full orbit back to their point of origin. They never leave the orbit but still they orbit.

180 degrees per second is 30 rpm. If you were correct it would be 60.

Try to understand that a U-turn on a roundabout is not a full orbit. Any analysis based on this comparison is therefore flawed.

A planetary orbit will have the satellite getting back to the same point after one lap and moving in the same direction. This is fundamentally different to the U-turn.

If you can't see this, then think of it this way.

A U-turn in a road would be 180 degrees, surely you would admit that.

This is physically equivalent to a U-turn on a mini roundabout, which is equivalent to a big roundabout.

Yes a U turn in a road would be 180 degrees FOR the car. If it drove around the block seven times to get there you wouldn't say that was the same as if it spun on it's axis like a fork lift. You are replacing what was being talked about, orbiting a roundabout with a false equivalency. You can drive 12 miles and end up in the same place you still drove 12 miles.

So...

A u-turn is 18p degree rotation and the size of shape of the roundabout is immaterial.

If you drove round it 7 times you would have done 7 x 360 degrees and be carrying straight on (dizzy)

Add an extra half lap +180 degrees and you have done your inefficient u turn.

[Graveworm]

As I said we were talking about describing and measuring what happened on the roundabout not trying to describe what happened to the car after if finished.

Take a look at a globe on the prime (Greenwich) meridian you are at 0 degrees. At 180 degrees where are you? Does that change depending on which way you are traveling or facing? If you went all around the world back to where you started how many lines of longitude would you pass. That's how the world describe moving around a circle.

I didn't say driving around even the smallest roundabout was driving around 180 degrees, that's 360 degrees. I said the vehicle rotating half way turned through is 180 degrees and it would be travelling at 180 degrees to where it was driving before driving around the roundabout.

They are different and seperate things.

We don't need to know where the car joins or leaves the roundabout or what direction it is facing to describe it driving around.
If it's at 6 o'clock and drives to 12 o'clock it hasn't driven 0 degrees around the roundabout it's 180 degrees. The same would be true for 3 - 9 or any 2 points you like at opposite sides of the roundabout.

But say it was 0 degrees, then why when it drives from 12 o'clock back to 6 is that 180 degrees? Why if it continues to 12 o'clock again, this time do we go from 180 to 360 when all it has done is drive another 0 degrees.?

12 o'clock to 12.30 is the minute hand pointing up to the minute hand pointing down - 180 degrees which is the rotation of the car. 12 00 to 12.00 is 360 degrees which is the orbit of the roundabout to get back to the origin.

Edited by Graveworm on Monday 11th December 01:02

[bmwmike]

Undertake in L1 but with the horn held down to make them aware is surely the right answer.

Or the old L1 L2 flash L3 straight back across their bows to L1.

[snuffy]

If a car performs a U-turn, it has described a semi-circle. So whilst it's now facing the opposite direction, it has travelled 180 degrees. But it is not back at the place at which it started; it's at the opposite point to where it started.

In order to leave a roundabout at the same point at which it entered, it needs to perform another U-turn, i.e. another 180 degree turn, giving a total of 360 degrees.

It does not matter if that U-turn is on road, round a mini-round about, or a huge roundabout over a motorway.

[911hope]

snuffy said:

If a car performs a U-turn, it has described a semi-circle. So whilst it's now facing the opposite direction, it has travelled 180 degrees. But it is not back at the place at which it started; it's at the opposite point to where it started.

In order to leave a roundabout at the same point at which it entered, it needs to perform another U-turn, i.e. another 180 degree turn, giving a total of 360 degrees.

It does not matter if that U-turn is on road, round a mini-round about, or a huge roundabout over a motorway.

Think about the fact that doing a u turn on a roundabout does not have you entering and exiting at the same place. ( Other side of the road ).

Just like any other U-turn, which is is 180 degrees.

Circle you turn around can be any size. 1cm or 1000km.

[Graveworm]

911hope said:

snuffy said:

If a car performs a U-turn, it has described a semi-circle. So whilst it's now facing the opposite direction, it has travelled 180 degrees. But it is not back at the place at which it started; it's at the opposite point to where it started.

In order to leave a roundabout at the same point at which it entered, it needs to perform another U-turn, i.e. another 180 degree turn, giving a total of 360 degrees.

It does not matter if that U-turn is on road, round a mini-round about, or a huge roundabout over a motorway.

Think about the fact that doing a u turn on a roundabout does not have you entering and exiting at the same place. ( Other side of the road ).

Just like any other U-turn, which is is 180 degrees.

Circle you turn around can be any size. 1cm or 1000km.

Forget which way the car is facing or travelling when it leaves the roundabout as that is not what was being discussed and has nothing to do with describing how far around a roundabout it traveled.

Again the circle you drive around is approximately 360 degrees or exactly 360 if you return all the way back to the beginning, there are some track entrances to roundabouts so a full 360 is possible. It doesn't matter if it is 1cm or 1000km. The car, if it drives off in the opposite direction is at 180 degrees to where it was before it entered the roundabout, but it has driven 360 degrees around a circle to get there. You keep describing the effect on the car by driving around the roundabout not the roundabout.

Consider the case if a car is already on the roundabout or started and finished it's journey on the roundabout. Even if you have no idea where it enters or leaves or indeed if it never enters or leaves and just drives around how can you describe how far it travels around the roundabout in degrees?

Edited by Graveworm on Monday 11th December 11:41

[911hope]

Graveworm said:

Forget which way the car is facing or travelling when it leaves the roundabout as that is not what was being discussed and has nothing to do with describing how far around a roundabout it traveled.
Again the circle you drive around is approximately 360 degrees or exactly 360 if you return all the way back to the beginning no matter if it is 1cm or 1000km. The car if it drives off in the opposite direction is at 180 degress to where it was but it has driven 360 degrees around a circle to get there.
What if a car is already on the roundabout or started and finished it's journey on the roundabout. Even if you have no idea where it enters or leaves or indeed if it never enters or leaves and just drives around how can you describe how far it travels around the roundabout in degrees?

And subtracted 90 degrees at entry and another 90 at exit. 360-90-90=180.

That's why it is equivalent to a u turn, which is 180 degrees.

Consider a motorway roundabout where it is common to enter from a slip road at a tangent to the circle on the left. Turning from where you came would have you leaving at a tangent on the right after a 180 degree rotation (a semi-circle). In this case the left turns on entry and exit would not apply.



The best way to address this subject is using the maths to find the accumulated rotation.

Co

[Cliftonite]

PLEASE stop all this off-topic roundabout stuff! It has all been discussed so many times before!

You are just going round in circles!

[911hope]

Cliftonite said:

PLEASE stop all this off-topic roundabout stuff! It has all been discussed so many times before!

You are just going round in circles!

Left turn -90
Straight on 0
Right turn +90
U turn +180
Left turn after a go-around +270...

.....Where it all started....
.....and correct.....


Guess what 360 is....all the clues are above.

[Graveworm]

911hope said:

Graveworm said:

Forget which way the car is facing or travelling when it leaves the roundabout as that is not what was being discussed and has nothing to do with describing how far around a roundabout it traveled.
Again the circle you drive around is approximately 360 degrees or exactly 360 if you return all the way back to the beginning no matter if it is 1cm or 1000km. The car if it drives off in the opposite direction is at 180 degress to where it was but it has driven 360 degrees around a circle to get there.
What if a car is already on the roundabout or started and finished it's journey on the roundabout. Even if you have no idea where it enters or leaves or indeed if it never enters or leaves and just drives around how can you describe how far it travels around the roundabout in degrees?

And subtracted 90 degrees at entry and another 90 at exit. 360-90-90=180.

That's why it is equivalent to a u turn, which is 180 degrees.

Consider a motorway roundabout where it is common to enter from a slip road at a tangent to the circle on the left. Turning from where you came would have you leaving at a tangent on the right after a 180 degree rotation (a semi-circle). In this case the left turns on entry and exit would not apply.



The best way to address this subject is using the maths to find the accumulated rotation.

Co

It's not rotation it's orbit. But if you turn 90 degrees left then 90 degrees right you have turned 180 degrees you are just facing in the same direction you started that's not the same as never having turned. You can't subtract anything it's like saying drive a mile north and a mile south you have driven 0 miles instead of 2.

But this is done you keep repeating the same without any source for it, loads of people have tried to correct you and many sources have been posted so have a great Christmas

[911hope]

said:

Get a maths book for Christmas.

[Graveworm]

911hope said:

said:

Get a maths book for Christmas.

Sounds great whilst I was waiting I went to the department of Maths at Berkeley and they gave me this to tide me over.
https://math.berkeley.edu/~gbergman/misc/numbers/3...

University of Berkley maths depth said:

... suppose you are driving, and come to a roundabout (a little circle in the road that you have to drive through). If you go 180° around the roundabout and exit, then you are continuing in the direction you started. You must go 360° around to go back where you came from

[donkmeister]

Can we just talk in radians please?

We'll still argue over whether it's pi or 2*pi, but at least we'll have pi(e).

ETA I can't be arsed to show my working but if you have linear momentum, then apply a centripetal force to orbit 2*pi radian, then remove said force and resume your original course, there has been a zero change in linear momentum. Whereas a 1*pi radian turn would invert the direction of said momentum. So, physics agrees that a 360 turn is a full lap of the roundabout and resuming the original course. Whether you are going on the car rest frame or the roundabout rest frame is irrelevant to the answer.

Edited by donkmeister on Monday 11th December 19:48

[donkmeister]

Graveworm said:

911hope said:

said:

Get a maths book for Christmas.

Sounds great whilst I was waiting I went to the department of Maths at Berkeley and they gave me this to tide me over.
https://math.berkeley.edu/~gbergman/misc/numbers/3...

University of Berkley maths depth said:

... suppose you are driving, and come to a roundabout (a little circle in the road that you have to drive through). If you go 180° around the roundabout and exit, then you are continuing in the direction you started. You must go 360° around to go back where you came from

This, for me, is the plumbing argument. Is it a 45 degree bend or a 135 degree bend? Had that one a few times

[mko9]

What if the entire roundabout is on a giant turntable that rotates in the opposite direction and at the same rate as the steering input?

[Cliftonite]

Roundabouts!

For Pity's sake, please STOP IT !!!