Task 24

Materials and tools for a working group:

board, wooden block, ruler, plasticine

In addition to weight, the level of the friction force that acts in the opposite direction depends on the size of the surface by which the article is placed against the pad. This means that if we have the object we want to move, it is advisable to place it on the side that has the smallest surface, resulting in less frictional resistance when moving on the mat. The task is formulated inductively, so the teacher does not express this thesis, but suggests a research question in the word: Does the size of the friction force depend on the surface by which the object touches the surface on which it moves?

After introducing a research question the teacher discusses with pupils theirpredictions and the way in which this phenomenon could be explored. As the task is formulated inductive way, it is important to use the procedures suggested by the pupils if they would provide sufficiently credible (objective) data to unambiguously verify the proposed predictions.

If the teacher does not have sufficient time for proposing investigation procedures, he/ she can offer the pupils procedure prepared in advance (as shown in the table in Task 21). However, in this case, he is assured that pupils perceive the link between the proposed procedure and the research question.

To carry out the verification, pupils will need a block whose sides are significantly different. To verify that a larger frictional force is exerted on the object when it is lying on the surface by larger side, they use the same board lift procedure as in Task 20. Pupils should find out that the smallest friction occurs when the object moves along the smallest side (in the case of picture is page B). The problem arises somewhat with the stability of the object, especially when it is built on side B. Sometimes the cuboid tends to overturn before it moves. To prevent this, we can reduce the center of gravity of the cuboid by gluing plasticine pieces around the perimeter of the sides of the block. If we do, then we have to stick the same piece of plasticine to the cuboid also in other tested situations (when the cuboid stands at the edge of A, and C), so that we do not change the weight of the object, since the magnitude of the friction force also depends on the weight of the object that moves along the pad.

They will verify their predictions and try to conclude on the basis of the measurements. At the end, they can evaluate their predictions and also answer the research question about the relationship between friction and the size of the surface by which the object slides on the board.