3 CHANGING THE MOVEMENT OF AN OBJECT REQUIRES A NET FORCE TO BE ACTING ON IT

Task 10

Materials and tools for a working group:

material for pulleys and pulley blocks production according to worksheet instructions, dynamometer

The aim of the task is to investigate the combination of fixed and free pulley, where in this case it is not just a comparison, but also a quantitative measurement, that is why the effort exerted will be expressed by the value of the variable (measured on the dynamometer scale). In the first part of the task, pupils construct individual pulleys and use a dynamometer to measure the force needed to lift the load. They write down the data. In order to develop the ability to measure, it is advisable to encourage the pupils to repeat the measurements, so they repeat the measurement for each situation three times and enter all the data in the prepared fields in the table. Alternatively, it is possible to obtain data the way that each group carries out one measurement and provides the measured values each other. Here, however, the values may vary, giving a place to discuss what may have caused differences in the measured values. If the measurement is done the same way, everyone must get the same results. If the results were not the same, the measurement was probably not exactly the same. Being aware of this connection also belongs to the development of the idea of the science process.

The task is partly constructional in nature, since the design of a free pulley assembly requires design thinking and skills. Working with measured values is more or less naturalistic; the pupils conclude from the measured data. The teacher can help pupils to draw conclusions by drawing their attention to trying to evaluate when the pulling of the load is easiest. An essential part of the conclusion is the reference to measured data. This means that the pupil must support his/her conclusions with the measured data, thus ensuring that the pupil argues the outcome of his/her observation. The process of argumentation is an essential element of the development of scientific communication.

In order to make the conclusion easier and at the same time to learn how to convert the obtained data into a graphic form, their task is to record the measured data into the prepared diagram. In order not to calculate the average value of the three measured values, they record all measured values in the diagram. Students should have a graph in which the first two sets of columns are approximately the same (the same force is needed to pull the load with a fixed pulley and without a pulley), the pulley value is halved and the pulley value is reduced again. The decreasing tendency of the diagram clearly shows which pulley design makes it easier for us to work. It is also interesting to discuss with children why a fixed pulley is used if it does not reduce the force needed to pull the load. Pupils can try to find an explanation online and further discuss the findings.