I.2. The stages of performing an experiment

Practical activity is one of the main tools of human knowledge and it is natural that in learning physics, science par excellence experimental, it should provide the most appropriate evidence to substantiate the theory. Learning physics through experimental activity will be the most challenging and interactive way, producing a permanent incentive and a positive attitude towards the content of the lessons and not just a passive assimilation of knowledge.

The experiment represents a reproduction, with the help of special devices, of the physical phenomenon during the lesson, in the most favorable conditions for its study.

🔦 Remark

The experiment serves both as a source of knowledge and as a method of learning. To experiment means to intentionally cause certain phenomena, under certain conditions, to study them and the laws that govern them.

Observation and measurement are fundamental activities in physics. Starting from the observation of some natural phenomena experiments are performed in the laboratory, in which measurements are made in order to find the physical laws and mathematical formulas that govern the studied phenomenon.

To perform an experiment you have to go through the following steps:

1) Establish your goal in the proposed experiment (for example, measuring some quantities, studying a phenomenon, studying the operation of a device, demonstrating some laws, etc.).

2) To identify the theoretical notions useful in carrying out the experiment.

3) To procure the necessary materials.

4) Strictly comply with labor protection rules to prevent injuries.

5) Respect the way it works.

6) Carry out the experimental determinations and, if necessary, record the data in a table.

7) To process experimental data.

8) Identify sources of error.

9) To formulate conclusions regarding the objective of the experiment.

👀 Experiment: How to determine the density of a magnet

Needed materials:
3 natural magnets of different sizes, scales or scales, water in a graduated cylinder, ruler, graph paper (math sheet).

Experiment description:

• Weigh each magnet in turn to determine its mass.
• Measure the volume of each magnet with the graduated cylinder.
• Fill in the data in the following table and process it.

• Gives the result of the measurement:

• Graph the body mass according to its volume. You will get a straight line. If you choose an arbitrary point on the right, you will find the body mass at a certain volume. For example for the red dot: we have m = 18,5 g and V = 4 cm³ .

What do you notice?

For a certain substance, the higher its mass, the higher its volume.

Experiment conclusion: Density is a constant for a particular substance, being equal to the ratio of mass to body volume.

👀 Experiment: Experimental verification of Pythagoras' theorem.

Needed materials:
Ruler, graph paper (math sheet).

Experiment description:

• Draw three right triangles of different sizes on the graph paper.
• Measure, for each, the length of the hypotenuse (the side opposite the right angle) and the two legs (catheti).
• Fill in the data in the following table and process it.

What do you notice?

The more the hypotenuse squared, the more the sum of the squares of the legs (catheti) increases.

Experiment conclusion:

• In a right-angle triangle, the square of the hypotenuse is equal to the sum of the squares of the two legs (catheti).

🔐 Apply what you have learned: Homework

In the three right-angle triangles from experiment no. 2, draw the height corresponding to the hypotenuse and note the foot perpendicular to the hypotenuse.

Using the ruler, measure these heights and the projections of the legs (catheti) on the hypotenuse.

Complete your determinations in the following tables and process the data:

Compare the results obtained in the last two columns of the table and draw the conclusion of your experiment. The equality you get is called the The Height Theorem. Write the statement of this theorem.

Compare the results obtained in the last two columns of the table and draw the conclusion of your experiment. The equality you get is called The Leg (Cathetus) Theorem. Write the statement of this theorem.