Physical qualities (volume, force, time, weight)

Volume

Volume measurement means measuring of the space that the measured substance or body occupies.The measuring instrument for volume measurement is a graduated cylinder. It can directly measure the volume of liquid or powdered substances. We measure the volume of the solid body easily by immersing it in water (or other liquids). The volume of the measured body is determined by the difference in volume of water before it is immersed and submerged. A graduated cylinder can also measure the volume of gaseous substances. Just fill it with water and turn it into a container with a little water so that all the water stays inside. We then use the tube to blow the measured gas inside.The graduated cylinder can be easily made from any container of a suitable size (for example, a PET bottle) by filling it with a known amount of water and gradually drawing the scale. However, beware of a systematic error! Every physical measurement is subject to error. If the error is predominantly positive or negative, proportional errors can be added with a sequential pouring. Therefore, it is advisable to pour out the water after few steps and check the applied scale by pouring in a known amount of water.Such a graduated cylinder can be used for making a spirometer (an apparatus for measuring the volume of the lungs. The volume of the lungs of a grown up man is roughly 4.5 litres so it is useful to use a 5 Litre jerry can.

Weight

Scales based on different principles are used to determine weight. Balance scales that are common function on the principle of comparing the weight of an object of unknown weight to known weights. The most commonly used scales, however, are those working on the principle of deformation of elastic body (for example the spring).The scale can be easily made from common office supplies. A spring, a rubber band and a ruler can be used. We firmly fasten the deformed object at one end and deform it by the load of the other end. Nearby we place a sheet of paper on which we draw the scale while using known weights.

Time

Time was recorded and determined already in the period before the Neolith (8 000 B.C.). From the beginning, the natural phenomena that repeated with regularitywere used to determine the current period. The most obvious and easily observable objects, which showed the highest accuracy in their periodical repetitions, making it possible to determine accurately the current period, were the Sun, the Moon and stars. However, it was not easy to determine accurately the current time or the season. Therefore, more understandable methods of measurement had to come. Primarily, from practical reasons which was time telling. To measure the time hourglass or water clocks, which work on the same principle (the liquid or the sand poured out from the top container into the lower container in a certain time) began to be used. Although you would not be able to read what time, it was from these. For this purpose, another system began to be used – the sundial.

How to make a sundial

It is not difficult to make a sundial. A rod stuck in the ground or fastened to a vertical surface will suffice. Then you only need to watch the time on your watch and record the position of the shadow every whole hour. Sundials can also be made from paper.For the sundial to work correctly, the pointer must have a direction parallel to the earth axis. For our latitude, this means a slope of the pointer roughly 50° from the horizontal direction, pointing north (Fig. 1). If the clock is placed on a vertical wall, the pointer must be around 40° vertically and facing south when viewed from above.

Due to the earth‘s axis inclination and the ellipse‘s trajectory of the Earth round the Sun, the Sun does not move evenly across the sky during the year. Therefore, during the year, sundials are gaining time or are delayed. The difference against the even time that the watch shows is up to 16 minutes. Therefore, the sundials are equipped with a correction table (Fig. 2).According to the current date, we find the value in minutes that must be added or subtracted in the table.

When designing the sun clock, we have two options:

1. We can set the right solar time on the dial. The clock is then equipped with a correction table including the correction to the longitude.
2. When calibrating the dial, we include the time delay given by the longitude. The clock is then provided with a correction table that includes only the correction by date.

Force

Dynamometers are usually based on the principle of deformation of elastic body (especially the spring). Based on this principle, a dynamometer can be constructed using ordinary materials in order to measure the tension force. A rubber food hose (approx. 3 m long) will suffice. We will tie one end of the hose to the firm handle. Gradually, all pupils will pull at the other end. Whoever pulls the hose most, applied the greatest force. For the objectivity of the measurement it is advisable to draw a line on the hose and to plot the best performances on the paper located nearby. If we attach the hanging weight to the hose and then pull it, we can provide our dynamometer with a regular scale in Newtons. Another non-traditional and very simple dynamometer measuring the strength of the press is a PET bottle.We will fill it with water, put matches of a various length into the bottle and we will close it. This is the principle of a physical toy called Cartesian diver. If we squeeze the PET bottle, the air contained in the matches is compressed and water is pushed into the volume of the matches. The density of the match increases and it begins to fall to the bottom. Since each match is of a different length, a different force is needed to sink it. Whoever sinks more matches wins. Be careful, the matches will soak in the water and the dynamometer stops working