Task 23

Materials and tools for a working group:

• board, jar with lid, ruler (measuring tape), water (eventually prasticine)

The goal of the task is to find out whether the friction depends on how heavy object is moving on the surface. First, the teacher discusses the predictions with the pupils, introducing the question so that the pupils understand it the same way. The task is to propose a procedure how the pupils would find that they need more strength to move a heavier object. After making predictions, the teacher discusses them with the pupils. Further they choose one of the proposed procedure (if it is appropriately credible) or follow the procedure proposed in task 20. The procedure for verifying the prediction is that we place the object we are examining at the top of the board, which we begin to lift slowly. At the moment when the container begins to slide over the surface of the plate due to the constant force of gravity, the pupils measure the height at which the plate had to be lifted to force the object to move the object on the inclined plate.

Since the objective of the task is to find out that friction depends on the weight of the object, pupils use a jar with a lid for thisinvestigation, for example a plastic food container with a lid. To keep the size of the object the same, they gradually add different amounts of water or plasticine to the container and examine whether the heavier container slides later. If the pupils use plasticine to increase the weight of the container, it is advisable to fasten the plasticine to the container so that it does not move during the tilting of the plate in the container, which can impact the container wall and move it over the plate before moving the plasticine in the container.

Pupils repeat each measurement the three times to obtain three numbers for each of the three situations. On the basis of these data, they formulate a conclusion in terms of verifying predictions and answering a research question related to the magnitude of the frictional force and the weight of the object.