Salty Sam’s Fun Blog for Children
Number 504
Radar
Hello Everyone
There are many craft that pass by my lighthouse, large and small.
Captain Jack brings his boat full of summer visitors around several times a day and l wave to them, if l have time.
There are sailing boats and motor boats and the odd fisherman too.
But the most beautiful of all are the sleek, gleaming-white luxury motor yachts that l occasionally see.
You will notice that on top of the highest part of them there is always a revolving part.
This is their radar.
The radar on board is just one of their modern navigational instruments along with GPS, sonar used to detect the depth of water under the boat and other sensors they have on board.
They can use their radar to detect any craft that is around them at a distance.
The radar can detect distant objects and tell the captain where they are and how fast they are travelling and in what direction.
Marine radars like this are used to prevent collusion with other ships and also to navigate. The captain or navigator can fix the position of their boat by picking up signals from things they can see on their map (called a chart) like islands, lightships and buoys that emit signals.
ln ports, vessel traffic service radar systems can monitor ship movements and regulate those movements if the area is busy so that collisions can be avoided in any crowded places.
Radar signals are reflected off and scattered in many directions by materials that have good conductivity of electricity like metal and water. (That means they let electricity pass through easily.)
Some signals will be absorbed but enough bounce off an object to be monitored by the device sending out (or transmitting) the signal (or radio waves).
lf the object is moving towards or away from the transmitter, there will be a slight change in the frequency of the signal due to the Doppler Effect.
You will hear the Doppler Effect in action when you notice a vehicle with a siren race past you on the street.
The siren sounds different as it comes towards you compared to when it is going away from you. This is because the sound waves in front of a moving vehicle move at a different frequency compared to behind it.
The Doppler Effect is sometimes also called the Doppler Shift.
Radar receivers are usually in the same place as the transmitter, but don’t have to be.
What you see revolving at the top of a boat is the receiving antenna.
lf you have ever tuned a radio to a radio station, you have been picking up radio signals at different frequencies as you turn the knob.
A radio station will broadcast its shows using a frequency unique to it.
The frequency will have a number followed by (kHz) which stands for kilohertz.
Radar is actually an acronym. The letters that make up the word stand for radio detection and ranging.
The beginning of radar started with experiments carried out by Heinrich Hertz in the late 1800s.
He proved the existence of electromagnetic waves. One of these electromagnetic waves we call radio waves.
Hertz found out that radio waves were reflected by metallic objects.
This is why radar can be used to detect ships and aeroplanes.
(Hertz is a word used in science today. lt is contained in the word kilohertz.)
At the beginning of the next century, other systems were developed using the principle. A system like this could be very useful for ships to avoid each other in the fog when they could not see each other – in the day or night.
During the 1930s, modern radar systems were developed by several countries as top secret projects. War was brewing.
Modern radar uses short pulses of radio energy to detect surrounding objects.
Once the war broke out in 1939, the work was speeded up and the development of the magnetron in the UK meant that relatively small systems could be built to use in the war effort. Being so small, the system could be carried on an aircraft – and even submarines could be seen from the air.
The magnetron was more powerful and accurate than anyone else had been able to produce.
Radar could be used on ships and submarines too.
Radar could be used on the ground to detect enemy planes approaching. Anti-aircraft guns could be manned and ready for action.
lt could be used to detect ships off the coast.
The magnetron was a significant invention that helped to win the war.
Pilots could find their way in the dark.
The population was told to eat carrots to gain this superpower. Carrots have Vitamin A which is good for your eyes. (Too much Vitamin A is bad for you.)
The radar developments were secret.
During war, money and resources are often found to help speed up scientific developments if they are thought to be useful in order to secure victory.
Nowadays, radar systems have lots of different applications.
They are used in medicine allowing doctors to see inside the body or set up heart monitors and the police use radar guns to catch speeding motorists.
Radar guns only detect speed not position. They are sometimes used by sports people to measure their speed of movement; like how fast they run or hit a golf ball.
Astronomers can use radar principles to help them detect the size and shape of objects in space.
Spacecraft visiting other planets have carried radar devices to map the surface of the planet they are observing and gathering data about.
Air travel has become safer. Air traffic control at airports uses radar.
ln the 1970s, ground penetrating radar was developed and this enabled archaeologists, architects and treasure hunters to look underground without digging it up first. This application is especially useful for people looking for unexploded bombs that have worked their way underground and can’t be seen from the surface.
But one use you will see every day of radar is the weather forecast.
The Meteorological Office uses radar systems to follow the movement of cloud formations and weather fronts in order to predict what weather patterns are coming our way.
They can see how clouds are being formed as warm air is rising and they can see thunderstorm activity.
They can even see the rate at which distant rain is falling!
During World War ll, military radar operators noticed that weather elements like rain and snow would create noise in the returned echoes they were monitoring.
After the war, scientists started working on developing equipment to make use of this phenomenon.
Ever since, the technology has been periodically updated.
Weather forecasts are especially important when weather warnings need to be issued to a nation; or at least an area of it; and they are constantly important to shipping. Weather warnings relate to heavy rain or snow or high winds.
Most radar systems are now designed to operate using radio frequencies that are not affected by rain or atmospheric gases; but weather stations use radio frequencies that will detect this kind of weather phenomena.
There are different kinds of radar.
Radar technology can be used for monitoring human activity too, which means the doors in the Rocky Bay Supermarket can open automatically for people pushing heavy trolleys – and foxes can set off security lights in your garden.
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And see you again next Fun Friday!
Love and kisses
Salty Sam
www.christina-sinclair.com
Bill and Bob’s Joke of the Week
Bill: When you see a half glass of water, do you see it as half full or half empty?
Bob: Well, technically a it is always full. lt may be half full of water, but also half full of air!
Salty Sam © Christina Sinclair 2015
Unauthorized use and/or duplication of material from this blog without express and written permission from this blog’s author and owner is strictly prohibited.
Links may be used to www.christina-sinclair.com
Picture Gallery
A studio used to create a radio show
Ship radar
Buoy
White is cloud and light blue is rain
A weather front
A weather front depicted on a map
The Doppler Effect
THE SALTY SAM NEWS DESK
This week, the children and I went for a long walk in the countryside.
You never know this time of year when the winter weather will suddenly hit and make you feel like you would really rather be inside.
We like walking in the autumn months.
Rocky Bay becomes less crowded as the holiday-makers drift off.
The colours of the leaves are beautiful.
In recent years, Bill, Bob, Emily and Henry have been busily collecting tree seeds to grow in pots. They grow them in their own gardens and they grow them in Auntie Alice’s garden too because there is far more space there. It is their contribution towards the trillion trees scientists say we need to plant to help with the problem of global warming.
Auntie Alice always says that it is better to do something about a problem than just complain about it.
The children use recycled items as pots to keep the cost down.
They use recycled items from their own kitchen like yoghurt pots and juice boxes and they collect them from neighbours’ houses too after they have been rinsed out.
This spring, they had more baby trees than ever that needed to be planted out so that they had plenty of room to grow.
They had already planted trees all over town!
I told you about how Auntie Alice set up a stall at the Rocky Bay Campsite in the summer and gave the trees away to the holiday makers there in exchange for a small donation to the Rocky Bay Animal Rescue Centre.
All the trees had to be labelled so that the people taking them would know they had room for a tree of that species. Some were taken as presents.
The children helped Auntie Alice and they all collected a nice sum of money and found lots of new homes for their trees.
They had three stalls in all over the month of August.
The trees were taken far and wide to find new homes.
So of course this autumn the children were out collecting seeds again. Some seeds, like conkers, are very hard to resist.
We have to take a bag with us because our pockets just aren’t big enough!
Sometimes you do get creepy crawlies caught up in the seeds but they run away when we tip the bag out again.
Of course, not all the seeds will grow.
Some are not ‘viable’.
But there will be plenty that will be.
Auntie Alice might set up another stand at the campsite next August and she might set one up at the Annual Rocky Bay Flower Show too.
After all, the Rocky Bay Animal Shelter will always need funds.
The children will have small saplings to sell.
And we just can’t resist collecting tree seeds.
A trillion is a very big number isn’t it?
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Quick Quiz
Do you know what these scientists study?
- geologist
- volcanologist
- botanist
- physicist
- zoologist
- astronomer
- chemist
- entomologist
- anthropologist
- ornithologist
lt’s the Weekend!
HOW TO MAKE A PRESENT SOCK
Is it too early to start making presents and decorations?
Probably not, if you have lots to make!
*You can make this sock as long as you want it to be by adding rows of knitting in the middle – to give you plenty of room for presents!
The project is made in garter stitch to make it robust.
If you wanted to make a few, you could embroider initials on them.
SOCK SIDE (KNIT ONE)
Using 4mm knitting needles and red dk yarn cast on 15 stitches
Knit 1 row
Increase 1 stitch at each end of the next 3 rows of garter stitch
Increase 1 stitch at the end of the next row
Knit 1 row
Repeat the last 2 rows 5 times (27sts)
Knit 7 rows
Decrease 1 stitch at the end of the next row
Decrease 1 stitch at the beginning of the next row (29sts)
Repeat the last 2 rows 3 times (35sts)
*Knit 51 rows of garter stitch (it is here you can add extra present room)
Change to white dk yarn
Increase 1 stitch at each end of the next knit row
Then knit 40 rows of garter stitch
Cast off
SOCK SIDE (KNIT ONE)
Using 4mm knitting needles and red dk yarn cast on 15 stitches
Knit 1 row
Increase 1 stitch at each end of the next 3 rows of garter stitch
Increase 1 stitch at the beginning of the next row
Knit 1 row
Repeat the last 2 rows 5 times (27sts)
Knit 7 rows
Decrease 1 stitch at the beginning of the next row
Decrease 1 stitch at the end of the next row (29sts)
Repeat the last 2 rows 3 times (35sts)
*Knit 51 rows of garter stitch (it is here you can add extra present room)
Change to white dk yarn
Increase 1 stitch at each end of the next knit row
Then knit 40 rows of garter stitch
Cast off
TO MAKE UP
- Sew around the red part of the stocking using red yarn and over-sew stitching with right sides together
- Turn the stocking the right way out
- Sew each side of the white part of the stocking using white yarn and over-sew stitching and turn the top down
- Crochet 30 chains into a length of white yarn to make a hanging loop and sew this into place
- Neaten all ends
Please note that the material on this blog is for personal use and for use in classrooms only.
It is a copyright infringement and, therefore, illegal under international law to sell items made with these patterns.
Use of the toys and projects is at your own risk.
©Christina Sinclair Designs 2015
Quick Quiz Answers
- geologist – rock formations
- volcanologist – volcanoes
- botanist – plants
- physicist – physics
- zoologist – animals
- astronomer – space
- chemist – chemicals
- entomologist – insects
- anthropologist – humans in historical and present societies
- ornithologist – birds
Embroidery Stitches
