IB Physics SL

Data and Observations

The Physics group decided to pursue the following goals during the field trip:

The results from these experiments gave us information on the physical aspects of the beach.

Purpose: to discover the frequency of the waves on the beach of Grumari Apparatus: Long measuring stick
Theory: f = 1/t
Procedure:

The measure of frequency was done by holding a long stick in the water and timing how much time it took for five waves to pass over the section and only the section where the stick was.
Done in the morning and in the afternoon in order to check the frequencies after the tides had changed.

Data Table #1: Frequency measured at 9:30 AM
Time taken for 5 waves to cross the stick:

Calculations of frequency:

Data Table #2: Confirmation of Results ( Measured at 9: 45 AM)
This experiment was done later at a shallower area (sand bank)

Data Table # 3: Frequency measured in the afternoon (1:00 PM)

Data Recollection:
From morning to afternoon and from shallower to deeper water there was no significant change in the frequencies of the waves.

Purpose: to discover the amplitude of the waves at Grumari.
Apparatus: Long measuring stick that had color changes at every 50 cm.
Procedure:

The amplitude of the waves was measured by holding the same stick used for frequency and subtracting the normal height of the water from the crest of the wave.

In Shallow water:

In Deeper water:

Yet these results are merely approximations due to the large scale used.
(The markings or color changes were only occurring every .5 m)

Purpose: to discover how deep one can see into the water.
Apparatus: Seechi Disk
Procedure: Unleash the string and let the disc sink into the water. Cease yielding string when the black marks on the disc become no longer visible.
Visibility: approximately 4 m

Purpose: to discover the slope of the terrain of the beach of Grumari.
Apparatus: Two long measuring sticks and string.
Procedure:

Place the two sticks at a certain distance in line with each other. Tie the string to each of them and adjust the string until its angle with the stick is perpendicular. Measure the two different heights of the sticks and calculate the slope.
Repeat this for each different terrain.

Analysis of Sand

Analysis of White Sand

Primary Dune:

Inter Tidal

IB Physics SL Conclusions

According to these soil samples, the sand tends to get thinner near the primary dunes and thicker near the water. This happens because the sand at the primary dunes has in its composition a lot of clay, which is the product of organic matter decomposition. Most probably this organic matter has existed in that soil much before the actual halophytes (plants which are tolerant to salt) have evolved. A theory, further explained in the group's conclusion, suggests that it might have been originated initially by glycophytes (plants which are not tolerant to salt) who had grown in the area and were killed by the high concentration of salt. Ever since then, the organic matter, which enables the growth of higher orders of plants in the area, has been renewed at every generation.
The sand is coarser near the water because it receives a lot of fragments of shells and crustaceans, often smashed by the frequency and strength of waves after they die and are brought to the beach by the currents.