Cut a small potato in half . On the cut face carve out a raised A . Do this for the other capital and small letters . Get a metal plate and put some big pins in rows and columns down this frame . Mount your potatoes with the letters arranged in the message that you want on this frame with the cut edges facing outwards . Now if you dip this frame in ink and then press it on a piece of paper you will have just printed the first page of your book !
Before the invention of printing each page had to be written by hand and any spelling mistake meant the whole page had to be done again , so books were expensive .With printing one man could print out hundreds of pages a day .
To print the second page one after finishing the first one just rearrange the potatoes on the frame to spell out the text for it . When all pages are finished bind them together in books .This is moveable type one of the most significant inventions of humankind which allowed millions to read books and was first done by Chinese and then reinvented in the West in 1400s .
Flying .
Humans can see that birds which are heavier than air do fly and so they tried to use the same flapping wings but failed .
Birds fly not because they flap but because their wings are curved like a shallow bowl turned upside face down on a table . As they move forwards air has to go from the front edge of the wing to the back over the curved surface and also below the wing . The top air has to travel a longer distance so it is more thinly spread out . Now air exerts a pressure in all directions and the top air because it is thinner cant exert the same downward pressure as the bottom air can exert upwards as it has more molecules per square centimeter .So the bottom air tends to lift the bird up .
The same principle holds in a plane . The wings are curved with the circular bit on top and flat underneath .As the engines drive the plane forwards air rushes across the top and bottom and provides lift . The heavier the plane the longer the wings you need . Recently humans have also flown 20 miles under their own power cycling with the feet but the wing spans needed were enormous and the material had to be very light .
Steam Engine
When a pot of water with a lid starts boiling the steam pressure lifts the lid up and can push it off . If you make a rubber ring round the lid margin then it becomes air tight and the steam cant escape and the lid lifts even more . Attach a rod to the top of the lid and it rises . When the steam cools down it creates a vaccum in the pot and the lid is pushed down . This up and down motion of the lid is used to drive engines .
The British were the first to invent it and use the power of the burnt coal to run their factories and conquered half the world with all the arms they made in these factories . Othe countries managed it later . The steam and the similar oil enginies are one of the most important human inventions ever .
Photography
Certain chemicals of silver when exposed to light become darker . The light reflected back from the white areas of the object or the person being photographed falls on the film at the back of the cameras and exposes the silver which darkens . The rest remains as before . In a dark room the film is washed to wash away the non exposed original chemical and only the original image remains.
Electric generator It was found that if a wire is moved up and down in a magnetic field ie between the North and South poles of a magnet , an ele ric current is generated in it . This current can be used to do work from the end of the wire . In a dam the falling water is guided so that it pushes such a wire up and down in a magnetic field and the electricity generated is then sent to homes . it is easier to have the wire wound round a magnet to get a circular motion .
Electric motor If an electric current is passed through a wire which is resting in a magnetic field it moves up and down . So electricity is converted to useful work .Electric motors and generators have given us goods and wealth undreamt of even by kings inm olden days.