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Don't forget towels and cloths!

Standard cubes for various materials can be borrowed from the physics learning workshop for a deposit. (Similar cubes are now also available in teaching material shops).

Appropriate measuring equipment is required to carry out the weight and volume measurements.

A set of scales is required as some experiments are to be compared with objects of the same weight in terms of their floating properties. You cannot rely on subjective feelings. For some people, a 100g piece of metal, for example, feels heavier than a 100g piece of plasticine due to its smaller volume. However, the respective objects must weigh exactly the same. As an alternative to measuring with the scales, you can also carry out a blind test in which the objects are compared blindly (i.e. with eyes closed or behind a box) while hanging on strings.

In order to be able to observe the water displacement well, the cross-section of the container in which the objects are tested should be as small as possible and adapted to the test objects (see also didactic background). A ml scale enables precise quantitative measurement. (Link to slides?)

Caution trap:

It is often stated that the buoyant force of a floating body is greater than the force of gravity or that the buoyant force predominates. This is technically incorrect. In a floating state, buoyancy and gravity are exactly equal. If this were not the case, the body would experience an upward force and would have to be accelerated in this direction. You can find more information here: (Link: to the technical background on buoyancy).

Children often encounter the topics of floating and sinking in everyday life. From these experiences, children often already have the prior knowledge that wood floats and metal sinks.

The physical phenomenon of buoyancy, which is related to the topic of floating and sinking, is fundamental to many other natural phenomena. The underlying laws also apply to gases, so many weather phenomena cannot really be understood without an understanding of the buoyancy of warmer air masses (and therefore air of lower density).

Experimental work in the classroom offers the opportunity to develop subject-specific methodological skills in the area of scientific working methods. To enable children to plan simple experiments themselves in the long term, it is important to repeatedly question and think through scientific methods together with the children, such as deriving a question from a phenomenon, formulating an assumption, considering the focus of observation, designing fair experiments (parameter variation) or documenting the results.

Every scientific topic should be used to initiate scientific ways of thinking and working. Keeping an eye on both target levels, the development of specialist knowledge and the development of scientific working methods, is a challenge in science lessons. In order to be able to plan the development of skills, the scientific working methods that can play a special role here are listed for the individual experiments.

However, the list under "References to scientific working methods" is not further specified. For example, under the point "Observing and targeted observation", both short and strongly guided observation tasks are conceivable, as well as longer observation tasks in which pupils reflect on the focus of observation. According to the Perspective Framework for Science Teaching (GDSU 2013), children should be enabled to answer questions increasingly consciously in experiments and also apply scientific methods increasingly consciously. The experiments are marked according to the subject level, but the different levels of competence development are not specified. The development of skills is taken into account insofar as the requirements for the scientific working methods in the listed experiments increase with the complexity of the content.

The experiments listed can therefore be used in lessons to increasingly use subject-related characteristics for comparative observation as well as to focus on an increasing number of characteristics. There are experiments (investigations) with simple observations (floats/sinks), as well as those in which immersion depth, displacement or buoyancy can be observed both qualitatively at first and later, if necessary, quantitatively and comparatively. While the documentation can be kept very simple for the simpler experiments in terms of content, a series of measurements naturally requires more comprehensive documentation, e.g. in a table. Both content and methods can be made increasingly complex.

One of the four ways of thinking, working and acting related to the scientific perspective is: "Trace natural phenomena back to regularities" With the ...., the ... relationship, a language pattern suitable for primary school is offered for a regularity. This is pointed out in the various experiments in which this language pattern also promises an increase in learning content.

Due to the complexity of the topic of "swimming and sinking", the topic should be well structured when preparing the lesson (see above). In the experiments, the material is already structured in such a way that the parameter variation is taken into account; only the volume or only the weight is varied. Considerations as to why it is necessary to change only one influencing factor (one variable) and keep the others constant can be made together with the children afterwards. For example, after exploring the relationships, you could consider whether the knowledge gained would also have been possible with experimental material in which the objects differ in more than just one size.

When investigating correlations, it is extremely important to only change one variable at a time and to keep other influencing factors constant (as far as possible). (This is known as the variable control strategy.) Knowing that variables such as color or surface structure of the object have no influence on buoyancy, these variables can be disregarded in the experiments. For children's research questions, it can be important to vary these parameters if an assumption (e.g. the surface structure could have an influence) is to be confirmed or rejected in the experiment. Depending on the children's preconceptions, assumptions and questions of this kind can play a role. It is therefore important to keep all conceivable variables in mind, even if only two parameters are specifically varied in the experiments listed. Scientists cannot know the result of an experiment (in this respect, they are like children). They have to plan an experiment in such a way that the result is as clear as possible. This also includes clarifying which variables could have an influence and deciding which variables should be kept the same and which variables should be changed, i.e. varying the parameters in a targeted manner. Children should use individual experiments in science lessons as examples to repeatedly think about decisions of this kind in order to learn the special method of gaining scientific knowledge.

However, there are a number of other scientific methods that need to be learned at primary level before the targeted variation of parameters can be understood. The topic of swimming and sinking offers opportunities for every age group in elementary school, as well as for differentiation within the class.

However, there are a number of other scientific approaches that need to be learned at primary level before the importance of parameter variation can be understood. The topic of swimming and sinking offers opportunities for every age group in elementary school, as well as for differentiation within the class.

For primary school pupils, density as a quotient of mass and volume is a difficult quantity to grasp

When it is worked out that weight and volume are important properties of an object that determine its buoyancy, an important insight is gained. (In later physics lessons, the distinction between the concept of mass and the everyday concept of "weight" plays an important role. In elementary school, this distinction would be premature).

Density describes a material property that determines buoyancy. As an intermediate concept, the weight of the material can also be used instead of density in elementary school, which in turn can be concretized and visualized using the weight of a unit cube.

However, an understanding of buoyancy as a material property is not sufficient to answer the question "Why does a ship float? To clarify the question of why a ship made of metal floats while a cube made of metal sinks, it is necessary to think beyond the concepts of the buoyancy of materials. Experiments, observations and considerations that take water displacement and buoyancy into account help here.

A special feature of the topic of swimming and sinking is that more sophisticated scientific methods can also be practiced, as the displaced volume, for example, can be measured and compared using very simple means. When working with water as a liquid, there is also the tactile aspect that the density of approx. 1 g/cm³ makes it easier to recognize and measure Archimedes' principle (see also technical background on buoyancy). Appropriate materials can be used to measure and calculate in the whole number range up to one hundred or one thousand in order to get to the bottom of Archimedes' principle.

It is important to structure this complex topic well in class. If both aspects of the topic (buoyancy of material and buoyancy of ships) are dealt with, it should become clear under which conditions the different explanatory patterns apply.

When investigating the buoyancy of materials, the relationships are easier for pupils to understand if the focus is on one parameter, either the weight or the volume, and the other parameter is kept constant when selecting the objects. In this way, an understanding of systematic parameter variation (see link on the structure of scientific working methods) can also be initiated (see Perspective framework for science lessons). The suggested experiments include experiments in which either the weight or the volume of objects is kept the same. (If necessary, see the link on the development of scientific working methods)

In the further investigation of buoyancy, the observation of water displacement is essential for understanding. The containers in which the buoyancy is to be tested must therefore be carefully selected. The cross-section of the container should be as small as possible so that the rise in the water level can be easily observed and must be adapted to the respective test objects.

The water displacement of an object cannot be specified in general terms, as the displacement depends on the position in the water: Floating objects, for example, displace more water when they are submerged than when they are floating. The sub-item Displacement (link) shows possibilities for structuring the choice of material.

Further experiments can be found here (link to experiments for pupils) to address common everyday ideas that are not very viable from a physical point of view and should therefore be changed in lessons.

Many people intuitively think that the weight of an object determines whether it floats or sinks in water. In fact, however, it is not the weight, as a heavy tree trunk, for example, floats, while a light pin sinks.

A simple rule can be formulated for objects that are completely immersed in water, such as a tree trunk or a pin: If the density of the material is less than the density of the water, then the object will rise to the surface of the water. If the density is greater, the object sinks to the bottom. Density is the ratio of mass (what we call weight in everyday life) and volume of a body; a common unit is g/cm³. (The same applies to other liquids with a different density).

If you put a metal toy boat on the water, the boat can float despite its higher density. However, if the boat were completely submerged, it would sink to the bottom. In this case, the buoyancy does not depend on the buoyancy of the material (as with a tree trunk or a pin), but the shape is a decisive influencing factor.

Further technical information on the question "Why does a boat float?" can be found in the buoyancy section.

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