Materials and tools for a working group:

Materials and tools for a working group:

balloon, string, straw, wool, thread, scissors

The task is partly focused on investigating the action of the friction force and also on the investigation of the effect of air resistance. The teacher starts the activity with a stimulating situation in which he inflates the balloon and further releases it. He discusses with pupils about what causes this object to move. In principle, it should be clear from the discussion that the force that causes the movement may not be often visible, but it certainly affects the body if it started to move (as in the wind or drafts). It is enough to generalize that the body moves due to moving air. Sometimes objects move in the direction of air movement (for example, in the wind stream, hair dryer, etc.), otherwise they move in exactly the opposite direction. In this case, it is the principle of the Newtonian Third Law, but the pupils are not yet able to understand it in this sense of action, so it suffices if they have enough experience of how this phenomenon behaves under different conditions.

The teacher asks the students if they think that how long a balloon is flying depends on how much we inflate the it. He suggests to try it out. He guides pupils to see how they will verify this prediction (see scheme in Task 16). The device needs to be made long enough, preferably through the whole class. If we inflate the balloon more, it will move quite a bit around the string.

Pupils try whether it works and then try to makepredictions according the table in the worksheets. First, they make a prediction for a balloon that is more inflated. They also create a predictionabout balloon shape. In this investigation, it is necessary to ensure the same inflation of two balloons of different shape, for example by using of a balloon pump. In principle, a wider balloon has more air resistance than a narrow balloon. However, the difference is only apparent with very large differences in balloon diameter.

Another prediction the pupils make and then verify is whether the distance the balloon will move on the string depends on string quality in comparison to the straw we use. The string is replaced by a thick, fluffy wool that fills the entire straw area and causes much greater friction. Conversely, a thin thread reduces friction, especially when it is a thread with a smooth surface or a nylon.

Similarly, they also investigate whether the distance the balloon is able to travel depends on how rough the straw we use is. The point is that pupils realize that it is not just a string, but also a straw that can change observed results. The question is whether these two surfaces rub against each other only in a small surface or around whole the inner perimeter of the straw. The larger the surface of the straw is, the greater friction we can expect, and the upward movement of the balloon.

To realize this, the teacher leads them to try to draw the image of the force on the balloon as they move (of course they only draw those they perceive). In addition to the gravitational force, they should also draw the direction of action of the escaping air on the balloon and also the frictional force that acts in the opposite direction as the balloon-moving force. After exploring, pupils try to draw a conclusion in which they generalize when the balloon gets the most.