1

Just Chat! / Re: What would chairs look like if our knees were on the back of our legs?

« on: 25/02/2013 13:25:34 »

I don't think chairs would look any different, though stools might be the better option since we might perch much like a bird rather than sit. The big problem might be getting your trousers on and off.

LOL...Can you imagine trying to ride a bicycle... 

2

Just Chat! / Re: Will my septic tank explode if I put dog poop down the toilet?

« on: 25/02/2013 13:17:48 »

Clever idea menageriemanor , my grandfathers thatched 300 year old cottage has no indoor toilet, only an "out house" of the "bucket & chuck it" variety. All the contents are buried in deep furrows between his rose beds, and I can tell you that they really thrive. After centuries of occupancy [ my ancestor built the cottage ] the soil around the cottage is unbelievably rich. The ashes from the fire are also added to the earth. I think our ancestors could teach us a thing or two about sustainable living. 

3

Physics, Astronomy & Cosmology / Re: Are Photons "pushed" or "pulled ?

« on: 25/02/2013 12:50:28 »

By the way, someone could complain that speed + direction = V is sloppy notation since you can't add a speed to a direction.

Yeah but you can tell from the context that the plus sign is being used as a logical and rather than a summation off terms, right?

Thank you PMB. Some on these pages have suggested my mathematics is weak, but although it's not great; it got me through electrical engineering.   

4

Technology / Re: is it possible to make a gun that could fire a projectile into space

« on: 25/02/2013 12:28:46 »

I would imagine they fired the gun at 55* to prevent overshooting the target and not because different laws of physics apply to German artillery!!!

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Technology / Re: is it possible to make a gun that could fire a projectile into space

« on: 12/02/2013 21:52:20 »

As far as I am aware a gun can achieve it's greatest velocity when fired at an angle of  45°. If this is the case what speed and distance would the projectile [that reached an altitude of 112 miles fired at near 90°] have attained had it been fired at 45°?

As far as I remember a gun will have it's greatest range , for a given muzzle velocity, when it's at 45 degrees (assuming a few things, notably a flat earth).
If I wanted the greatest muzzle velocity, I would point it down. gravity might not help much, but it would help.

In the real world, the usual model* for range doesn't work terribly well. The biggest problem is that it ignores air resistance.
If you are trying to ram air out of the way at hypersonic speeds, air resistance is hugely important.
45 degrees is no longer the "right " answer and a calculation of the range isn't going to be very good.
As an indication, the (lower bound to the) velocity I calculated for the HARP projectile was 1700 m/s. The real speed was about twice that.
* Like this
http://en.wikipedia.org/wiki/Trajectory#Uniform_gravity.2C_no_drag_or_wind

You say [if I read you right] that in the real world firing the projectile at 45 degrees s no longer the "right" answer! At what angle in your world would you fire the gun for maximum range?

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Physics, Astronomy & Cosmology / Re: Are Photons "pushed" or "pulled ?

« on: 12/02/2013 20:15:04 »

I thought speed + direction = V for vector?

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Physics, Astronomy & Cosmology / Re: Are Photons "pushed" or "pulled ?

« on: 12/02/2013 19:20:01 »

It's generally easier to talk about beams or pulses of light than photons, as quantum mechanical photons are odd beasts that don't really behave like little bullets flying along through the universe. 

So if we have a pulse of light, it's velocity can change, since velocity includes direction and gravity can deflect it.  It's speed doesn't change, since we measure speed locally, meaning as the pulse flies by us.  We could sit anywhere along its bent path and measure it to travel at the speed of light.  The total time it takes to go between two points will change if you put a large mass in the way, since light travels on a curve and even though it moves at a constant speed along that curve, the total distance it has to travel increases.

I am confused? What is the difference between velocity and speed?

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Technology / Re: is it possible to make a gun that could fire a projectile into space

« on: 12/02/2013 19:03:59 »

As I thought 90 degrees hits the ground before the  45 degree vector and 45 degrees has the absolute range of any cannon fired projectile .[/i]http://www.physicsclassroom.com/mmedia/vectors/mr.cfm

9

Just Chat! / Re: English queen.. What for?

« on: 12/02/2013 18:50:12 »

Let's not start an argument from a thread that has been dead for many years. 

Thanks
imatfaal / moderator

  I was unaware that responding to or giving ones opinion on an old post was forbidden. My sincerest apologies. What is the exact cut-off point for responding? Perhaps it might be a good idea to remove posts that you deem no longer active.

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Technology / Re: is it possible to make a gun that could fire a projectile into space

« on: 12/02/2013 18:39:40 »

Projectiles go furthest in the horizontal plane for a given muzzle velocity when fired at 45degrees to the horizontal (although I think this angle ignores air resistance)  - but the muzzle velocity itself is independent of the angle of inclination.

Surely a projectile fired in the horizontal would hit the earth sooner since it,s trajectory means that it begins to fall the moment it leaves the barrel?

11

Physiology & Medicine / Re: Does composition of breast milk differ for male or female babies?

« on: 12/02/2013 18:23:37 »

I would like to ask if mother's milk who just delivered a baby boy contains more or double the amount of nutrients than a mother who delivered a baby girl? I have just read that in an article but I would like to know if that is true or it is just a hoax. Thanks

What if a mother gave birth to mixed twins? I very much doubt that one breast had "Gold Top" on tap and the other "Semi Skimmed". lol...it must be a hoax. 

12

Physiology & Medicine / Re: Stress->Cortisol->Glucose->Diabetes?

« on: 12/02/2013 18:11:15 »

I have had type one diabetes for over 30 years. If I get annoyed I can actually feel my adrenalin glands pumping away and causing pain in my kidneys. The first and most obvious effect it has on a diabetic is to rapidly drop his blood sugar levels down to hypoglycaemic levels which causes very stressful and frequently uncontrollable rash behaviour and if untreated with glucose unconsciousness. Occasionally the opposite can happen and the blood sugar level will rapidly rise to hyperglycaemic levels, this is caused by the adrenalin activating glycogen, which is a type of glucose stored in the liver. When a person unaffected by Type 1 diabetes experiences stress or the fight or flight scenario their pancreas automatically stops pumping insulin into the blood stream. A diabetic is handicapped in this sense since their insulin injection regime means that there is always insulin in the blood and they are unable to "turn it of" so to speak. All of this has the effect of making diabetics prone to "flying of the handle" and living in a "high stress mode" which unfortunately makes them very susceptible to strokes, heart and kidney failure and aneurysms not to mention much more likely to pick up and die from infections that most people easily "dust off". 

13

Physics, Astronomy & Cosmology / Re: Are Photons "pushed" or "pulled ?

« on: 12/02/2013 16:54:33 »

Hi,JP. Thanks for the useful info and your ideas. But another question: If a photon which has mass and is travelling at light speed "can" be pulled by gravity, would that "pull" not add a net velocity to the photon?

14

Physics, Astronomy & Cosmology / Re: If a bomb explodes in space, is there a shockwave?

« on: 12/02/2013 16:36:29 »

I'm just watching Superman 2 and he explodes a bomb in space which releases the baddies  :0

Would it create a shockwave?

It would create a wave of expanding gases in which a shock wave would be propagated, there would however be little or no bow shock ahead of the expanding gases as would be the case in an tropospheric explosion. 

15

Physics, Astronomy & Cosmology / Re: Why does the Moon look large in a camera picture?

« on: 12/02/2013 16:27:49 »

The Moon appears small when viewed high up in the sky. The Moon appears vary large when viewed near the horizon. This is due to an optical illusion.
Our brain may be fooled, but surely a camera should show the actual size of the Moon at all times. Why is the camera being fooled too?

The moon only ever looks big in a photo if you took the picture with a telephoto lens. The 50-58mm standard lens on a 35mm camera negative barely show the moon as a pin ***** even though it looks as one would see it with the naked eye through the view finder. I never really understood this effect because the standard lens is very close to the perspective and image seen by the human eye, yet we perceive  the moon as quite large in the sky?

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Physics, Astronomy & Cosmology / Are Photons "pushed" or "pulled ?

« on: 12/02/2013 15:54:42 »

Just a muse, but are photons and other parts of the electromagnetic spectrum pushed or pulled after propagation?

17

Physics, Astronomy & Cosmology / Re: Could the weird shiny thing be part of a spacecraft?

« on: 12/02/2013 15:40:02 »

I'm just hearing about the "weird shiny thing on Mars" and so I looked up a picture. I'm wondering if it could be part of a spacecraft? NASA, ESA, the Russians and the Soviets have sent many probes to Mars, many of witch failed. There MUST be refined metal scattered around the surface of Mars.

I do agree that when we do learn what it is it will likely be boring. But how cool would it be to find a bit of refined metal on Mars?

I just took a look at the"weird shiny thing" on the net, and yes; it does indeed seem to be "a weird shiny thing!!!". If it is part of a space craft it's likely to have come from one off the Curiosity rovers own  descent stages.
The explosive bolts from the heat shield or part of the shield itself. Explosive bolts from the parachute shroud or again part of the shroud,the chute also had explosive bolts and clamps. The ingenious sky crane also had numerous explosive bolts and clamps. The fact that the "shiny weird thing" is so close to the landing site would leave me to believe that it is a part related to one of the descent stages probably the crane.

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Just Chat! / Re: Hi I'm Sheepy !

« on: 12/02/2013 15:19:24 »

Hi There,

I'm Sheepy !

I'm a newbie and I love all things to do with net curtains and I thought this site would be very apt for my net curtain fix. TNS  = The Net curtain Site yes ?

Looking forward to discussing net curtains and net curtain related issues with ewe all.


Here's a piccy of me posing in front of luffley net curtains....

 [ Invalid Attachment ]

Me Posing In Front Of Net Curtains Just Moments Ago

By way of reciprocal niceness ewe can post one of ewe in front of net curtains too !!



Hugs and shmishes


mwah mwah mwah !!




xxxxx

Keep well clear of Wales and Ballymena Sheepy!!!!!

19

General Science / Re: how can you make a glue formula

« on: 12/02/2013 07:37:47 »

A very good "glue" trap for rats can be made by filling a shallow baking tray with a mixture of cornflour and cold water. Mix it to it.s semi-liquid state and set your bait in the middle as soon as the rats feet hit the mixture it becomes rock solid and inescapable. 

20

General Science / Re: Is there a "potential energy" radio?

« on: 12/02/2013 06:58:05 »

No, I am not talking about some miracle energy device, I am talking about pulling up a mass and letting it drop (slowly with the help of gears) to run a generator.

Has anyone here seen anything like this to operate, say, a small radio?

I remember seeing a WW2 Japanese emergency radio beacon that used a weight and pulley clockwork drive. It was standard issue on their big bombers. If one went down and the crew survived they would set up the radio beacon on it's tripod and set the pulley in action the radio would then transmit an emergency signal. The Americans and British were not so lucky as they had to continuously in turns hand crank a radio attached to a dynamo. Not a nice job in tropical heat!!!