First easy access

Objective:

To make the buoyancy force perceptible for children, to teach the connection between buoyancy and water displacement

Plastic tub or bucket with a capacity of at least 5 liters (depending on the size of the selected immersion objects), preferably transparent

Different sized objects such as: Balloons, balls, bowls, pots, small bowls or similar.

If necessary, washable pen for marking on plastic tub or bucket

A small balloon, pot or similar is immersed in the water and a large balloon, pot or similar for comparison. The task is to feel which one requires more force.

Variations:

You can use a variety of objects for this experiment, but make sure you have suitable buckets or basins.

Hang a piece of plasticine, stone or other heavy material that sinks on a "fishing rod" and allow the weight to be felt. The further the body dives into the water, the lighter it feels until it is completely submerged.

Hang a piece of plasticine, stone or other heavy material that sinks on a rubber band. The deeper the object is submerged, the less the rubber band is stretched until the object is completely submerged.

It is easier to push the smaller objects under water.

The deeper an object is pushed under water, the more force is needed to push the object down (or the stronger the object is pushed upwards by the water). This is easy to feel when slowly pushing under water.

The following applies to balloons and balls: However, once the object is completely submerged under water (and has thus displaced the maximum possible amount of water), you do not need to exert any more effort to submerge it any further. Pots or small bowls may only be submerged up to the rim (if the vessels are submerged and filled with water, a much smaller amount of water is displaced and the buoyancy is no longer noticeable in most vessels).

When comparing, the water level can be observed or documented in parallel, see (link) Buoyancy regular relationship

When the larger object is immersed, the water level rises more than that of the smaller object until it is completely submerged, then it no longer rises.

Similarly with the heavy bodies "on the fishing rod": The deeper the body dives into the water, the lighter it feels, until the point at which it is completely submerged, see above. The observation described above is also possible for the water level.

Which object is pushed up more by the water?

Does the water push up equally strongly if the object is only pushed slightly under water or as far as possible (or completely in the case of balls or balloons)?

What happens to the water level?

The following applies to all questions: While working, always ask for the children's interpretation patterns, e.g. "Why do you think ...?" or have them write them down on the worksheet.

What else could you try out to find out when an object is pushed up strongly? What characteristic of the object does this depend on? (Children could guess: shape, surface, amount of water in the container, etc.)

Make assumptions and formulate questions - raise initial general questions, possibly initial assumptions

Observation and targeted observation - comparative targeted observation (short period of time) with the possibility of including a significant side event (water level rise) in the observation, possibility of reflecting on the focus - what are side events?

Verbalize observations, assumptions, findings and feelings as such

Describe facts and present them appropriately - Possibility of using worksheets to provide symbols, helpful language patterns or similar to familiarize students or to give students a free choice of presentation

If balloons or balls are used, terms such as pushing down air should be avoided. This would support the idea that bodies float if they contain air. This idea only partially captures the phenomenon of buoyancy. Buoyant forces also act on a stone (for example, it could be carried more easily in the water - or the buoyancy can be felt on the "fishing rod"); you will find ways to visualize this buoyancy in the experiment "Finding buoyancy regularity".

When preparing the water-filled containers, make sure that there is still enough space for the water to rise to the top.

Buckets or basins must be large enough for the objects that are to be immersed.

If the balloon (or ball) is suddenly released, it will shoot up out of the water. This may cause a lot of flooding, so it is advisable to let the children make their first explorations slowly and hold on to the balloon throughout. As the balloon bounces upwards, however, you may notice that the buoyancy acts upwards.

If balls or balloons are so large that they just fit into the bucket or pool, the question: "Which is more difficult to push under water - the small or large ball?" can lead to children finding the small ball more difficult as it has no guidance, so to speak. The question should therefore be asked more precisely, e.g: "Which object takes more force to push down?"

(Transparent buckets can be purchased relatively easily with a large portion of foam wafers).

Learning prerequisite: none, possibly experience with the gravitational pressure of water

The proposed material focuses the experiment on the different volumes of an object. In this way, the children's experiences are guided in a result-oriented manner. They are guided to recognize the dependence of buoyancy on the displaced volume of water. Without prior knowledge, children could also assume that buoyancy depends on surface properties (e.g. smooth or rough), shape or other factors. The shape is decisive insofar as a distinction must be made between solid and hollow shapes. In the case of ships, the fact that the hollow shape displaces more water and therefore has greater buoyancy is used. Other explanatory patterns of the children should be taken into account.

Feel the water pressure: If your hand is in a plastic bag, you can feel exactly how the gravitational pressure of the water presses the bag against your hand (provided no water gets into the bag!).

Tube on a funnel closed with balloon skin, the deeper under water, the more the balloon skin is pressed in, or water-filled balloon with tube and water column according to the Swimming and Sinking Manual (Möller) p. 23

Further experiments - differentiation possibilities:

Buoyancy quantitative relationship

Buoyancy qualitative relationship - Archimedes' principle

Experiments on pupils' ideas - Sinking object in a small or large container