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Calculating Pressure on Soil

By Nurhazizah, a teacher at SMP Labschool STKIP Muhammadiyah

Calculating Pressure on Soil
Students using bricks to prove the implementation of the formula for pressure as it applies in everyday life.

ABDAYA, ACEH –  Learning Science is often assumed to involve  mainly the memorization of formulae and testing them. Contrary to this assumption, as part of an investigation of the relationship between force, pressure, and the size of the area over which the pressure is exerted, I invited students to conduct experiments that facilitated their understanding of the material.

Initially, I explained the influence of pressure in everyday life, for example, most students' shoes become worn more quickly under the heel than at the front. Then we compared a sharp knife and a blunt one, and invited the students to observe the  difference between the feet of a chicken those of ducks.

Next, the students were divided into groups to conduct experiments. Materials provided included three bricks, rulers, pencils and a worksheet. Then, the students looked for the material they needed in the school yard. This was loose soil which becomes mud when it is wet.

Next, they placed the bricks in different positions on the mud. They compared the amount of pressure from each brick in different positions using a ruler to measuring the depth and breadth of the impression the brick had made on the mud.

The formula for the pressure exerted by the brick is the amount of compressive force divided by size of the area under pressure from the bricks, with the formula P = F/A, where P is the pressure, F is a compressive force and A is the size of the pressured area. Another example of this effect is when hammering nails; the pointed ones are easier to hammer in than the blunt ones.

"Today, we proved that the factors affecting the pressure are the amount of compressive force and the size of the area under pressure. The greater the surface area of the brick, the smaller the pressure generated. The smaller the surface area of the brick, the greater the pressure generated by the brick," explained Kamelia, an eighth grade student.


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