At the same time the Egyptians invented the ‘shadow clock’, other cultures also developed a need to organize their time more efficiently. Amongst others, the Chinese, Greeks and the Romans developed another device for telling the time known as a ‘sundial’. Sundials do not necessarily work better than shadow clocks; it is just a slight variation to the shadow clock. Make your own ‘sundial’ to tell the time in this science experiment:
WHAT YOU NEED:
• Stiff card
• Thick cardboard
HOW TO PROCEED:
1. On a stiff piece of cardboard, draw a right-angled triangle as in the diagram above. The short sides of the triangle should be about 150mm long, whereas the long side will be about 200mm, depending on the longitudinal angle used for your town. Make sure that you also add the base, below the dotted line.
2. Cut out the triangle, and make a fold along the dotted line to form the base for the triangle to stand on.
3. Make a thick base for your sundial out of corrugated cardboard or wood of about 150x300mm in size. Draw a semi-circle on the base as shown in the diagram above.
4. Glue the folded part of the triangle firmly to the base and place the sundial on a flat surface outside so that the triangle points north / south.
5. Mark the position of the shadow that falls on the base every hour. Notice that the shadow travels the same distance along the semi-circle every hour. On a sunny day you will now be able to tell the time by looking at the position of the shadow on your sundial!
In the above science experiment we have built a time indicating device called a ‘sundial’. This works because of the fact that shadows change direction, depending upon the time of day. The position of the sun in relation to a specific location on earth changes throughout the day as the earth rotates around its own axis every 24 hours. A ‘sundial’ like this one, uses a shadow’s position to tell the time. The position of a shadow on the semi-circle depends on the time of day, but it also depends on the season of the year. That’s because the sun’s position at a certain time of day is different in different seasons.
The obvious problem with ‘sundials’ and ‘shadow clocks’ is that they don’t work during nighttime! The king of Egypt, was not satisfied having to check the position of the stars to know what the time is during the night, so one of his princes made him a water clock. A water clock works by taking a big bucket of water, fills it with water up to a specific line and then cut a small hole in the bottom of the bucket and marked off lines on the bucket after each hour had passed. The problem with a water clock is that water flows more slowly or quickly when the temperature changes. The same principle was used but the water was substituted with sand to make a sand clock. The inventor of the sand clock is unknown, but the sand clock or hourglass was commonly used in ancient times and is still used today.