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4768 posts

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Topic # 86433 6-Jul-2011 20:36 Send private message

....are all the points inside the object moving at the same velocity?"


That advert is really bugging me.  His counterexample of the truck moving round the pivot is wrong because it isn't even moving at a constant velocity. Since velocity involves speed AND direction, not just speed and so traveling in a circle isn''t a constant velocity - it involves constant acceleration. (acceleration being a change in velocity)

So the fact that the objects inside the truck are not moving at the same velocity as each other is totally irrelevant because his first premise (that the object is travelling at a constant velocity) isn't even true

[/geek rant]

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671 posts

Ultimate Geek
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  Reply # 490301 6-Jul-2011 21:51 Send private message

I dont see travelling in a circle as being acceleration since the object is only changing the direction it is travelling - not knowing math, I believe it may be called angular velocity.

Given a central point, objects at the front of the car (facing that point) would move slower than those at the back of the car. I think this is because the radius of the circle would be larger for those at the back of the car and given the same time as those at the front they would need to travel faster in order to make it around the circle at the same time as those at the front of the car.

As I said, I dont know math, so just guessing.




TwoSeven



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  Reply # 490330 6-Jul-2011 22:32 Send private message

http://en.wikipedia.org/wiki/Acceleration#Circular_motion

"An example of a body experiencing acceleration of a uniform magnitude but changing direction is uniform circular motion. In this case, because the direction of the object's motion is constantly changing, being tangential to the circle, the object's velocity also changes, but its speed does not. This acceleration is directed toward the centre of the circle and takes the value:"



532 posts

Ultimate Geek
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  Reply # 490377 7-Jul-2011 00:26 Send private message

Both velocity and acceleration are vectors and acceleration is the change in velocity. So in fact for circular motion (or any other non straight line motion) there are two accelerations.

One is due to the change in the magnitude of the velocity vector and for circular motion that is tangential to the circle.

The other is due to the change in the direction of the velocity vector and is perpendicular to the velocity vector, so for circular motion it points to the circle's centre. This is the centripetal acceleration and for an object moving at constant speed its magnitude is equal to speed**2/radius. This results in a force on the object pointing to the centre of the circle as force=mass*acceleration.

Note that this is not the so called "centrifugal force" that we think we feel pulling us away from the centre of motion when in a car, for example; that is a ficticious force that does not exist. We are tricked into thinking it exists because in our own frame of reference, that being the inside of the car, we are motionless but feel the car under us being accelerated by centripetal force into the circle which we interpret for ourselves inside the car as an acceleration of us (and thus a ficticious "force") in the opposite direction.

It is important to note that if the plane in which the motion takes place is not horizontal gravity has an effect on the motion around the circle.


I knew my physics would come in handy one day (but in fact have also done a bit of this stuff associated with the behaviour of high powered boats :-) )

428 posts

Ultimate Geek
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  Reply # 490385 7-Jul-2011 07:17 Send private message

Well, not really caring about whether it is correct or not, I absolutely love this add. I'm sure it's really every blokes way of demonstrating a mathematics principle.

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  Reply # 490398 7-Jul-2011 08:33 Send private message

Vectors and scalars - now that's geeky...

Respect!

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Ultimate Geek
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  Reply # 490402 7-Jul-2011 08:40 Send private message

I haven't seen the advertisement - whose is it and what channels is it being played on?

Thanks



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  Reply # 490405 7-Jul-2011 08:46 Send private message

Byrned: Well, not really caring about whether it is correct or not, I absolutely love this add. I'm sure it's really every blokes way of demonstrating a mathematics principle.



The thing is, if he had actually said ‘speed’ instead of ‘velocity’ then he would have been absolutely correct. But instead the script writer decided to sound more scientific by using velocity, but instead ended up just being plain wrong.

298 posts

Ultimate Geek
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  Reply # 490411 7-Jul-2011 09:03 Send private message

NonprayingMantis:
Byrned: Well, not really caring about whether it is correct or not, I absolutely love this add. I'm sure it's really every blokes way of demonstrating a mathematics principle.



The thing is, if he had actually said ‘speed’ instead of ‘velocity’ then he would have been absolutely correct. But instead the script writer decided to sound more scientific by using velocity, but instead ended up just being plain wrong.


Agreed.  This is BASIC high school physics, and to get it wrong (IMHO) destroys the credibility of the message they're trying to send - albeit an otherwise valid one.  Kind of like having a big fat spelling mistake in the middle of a printed advertisment.




Things are LookingUp....  A photo from my back yard :-)
http://www.astrophotogallery.org/u141-rodm.html 

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  Reply # 490425 7-Jul-2011 09:25 Send private message

John2010: I haven't seen the advertisement - whose is it and what channels is it being played on?

Thanks


532 posts

Ultimate Geek
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  Reply # 490454 7-Jul-2011 10:08 Send private message

Thanks trig42.
I think that they must have edited the VW into an old Hilux ad as the mud, dog, etc all seems familiar. Smile  

223 posts

Master Geek
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  Reply # 490459 7-Jul-2011 10:19 Send private message

John2010: Thanks trig42.
I think that they must have edited the VW into an old Hilux ad as the mud, dog, etc all seems familiar. Smile  


Except the Amarok looks infinitely better than a Hilux!

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  Reply # 490834 7-Jul-2011 22:22 Send private message

Benjip:
John2010: Thanks trig42.
I think that they must have edited the VW into an old Hilux ad as the mud, dog, etc all seems familiar. Smile  


Except the Amarok looks infinitely better than a Hilux!


no way! hilux ftw 





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Ultimate Geek
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  Reply # 490909 8-Jul-2011 08:41 Send private message

LookingUp:
NonprayingMantis:
Byrned: Well, not really caring about whether it is correct or not, I absolutely love this add. I'm sure it's really every blokes way of demonstrating a mathematics principle.



The thing is, if he had actually said ‘speed’ instead of ‘velocity’ then he would have been absolutely correct. But instead the script writer decided to sound more scientific by using velocity, but instead ended up just being plain wrong.


Agreed.  This is BASIC high school physics, and to get it wrong (IMHO) destroys the credibility of the message they're trying to send - albeit an otherwise valid one.  Kind of like having a big fat spelling mistake in the middle of a printed advertisment.


Except I doubt the typical buyer of this product would be a high school physics type (excuse the stereotype).

I guess it's a bit like those movies that aren't technically acurate, or the dog that says "bugger" or Toyota's ad with the flying fox - you have to allow for a bit of artistic licence.

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Ultimate Geek
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  Reply # 490926 8-Jul-2011 09:22 Send private message

Byrned:
LookingUp:
NonprayingMantis:
Byrned: Well, not really caring about whether it is correct or not, I absolutely love this add. I'm sure it's really every blokes way of demonstrating a mathematics principle.



The thing is, if he had actually said ‘speed’ instead of ‘velocity’ then he would have been absolutely correct. But instead the script writer decided to sound more scientific by using velocity, but instead ended up just being plain wrong.


Agreed.  This is BASIC high school physics, and to get it wrong (IMHO) destroys the credibility of the message they're trying to send - albeit an otherwise valid one.  Kind of like having a big fat spelling mistake in the middle of a printed advertisment.


Except I doubt the typical buyer of this product would be a high school physics type (excuse the stereotype).

I guess it's a bit like those movies that aren't technically acurate, or the dog that says "bugger" or Toyota's ad with the flying fox - you have to allow for a bit of artistic licence.


Err no - not excusable.  The presenter is giving us a physics lesson and GETTING IT WRONG.  There is no excuse for that.




Things are LookingUp....  A photo from my back yard :-)
http://www.astrophotogallery.org/u141-rodm.html 

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  Reply # 490937 8-Jul-2011 09:42

Amarok sounds too much like Anorak
And Toureg... Toerag???

What wrong with VW and their vehicle naming?
Apparently their naming is all checked out in the US where anoraks and toerags are unkown. Seems the UK public has also been cringing..

Makes the Isuzu Mysterious Utility sound cool for gods sake!




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Nothing is impossible for the man who doesn't have to do it it himself - A. H. Weiler

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