Task 19

Materials and tools for a working group:

paper clip, magnet, paper, fleece, plasticine

The aim of the task is to find out that the intensity of the friction force acting against the movement of the objects on the surface depends on the object and the surface on which the object is moving on. The measurement procedure is the same as in the previous task. The principle is that the magnet attracts the paper clip from a smaller distance if it is on a surface that causes greater friction. I it is necessary to exert more force on it to move the object.

Pupils place the paper clip on the paper and find out from which distance it will be pulled by the magnet. As in the previous task, the magnet must always be approached by the same side (either the north or south pole of the magnet) to obtain comparable results. The measurements are repeated three times to eliminate any measurement error. Then they put the clip on piece of fleece and repeat the measurement. The third measurement is made with a paper clip placed on a thin plasticine layer. Research surfaces can be replacedby others, of pupils´ choice. Interesting results can be obtained, for example, by observing the attracting of a clip placed on a fine sand paper or laid on straws.

They will conclude from the investigation when greater friction occurs, i. when it is necessary to use more force to move the object placed on the surface and when, on the contrary, less. Pupils compare the surfaces on which the paper clip moved more heavily with those that moved more easily. Based on the observed similarities and differences, they try to characterize the properties of surfaces that reduce or increase friction. The more different surfaces the pupils try, the more credible results they obtain.