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

Task 7

WORKSHEET

Materials and tools for a working group:

materials and tools for constructing pendulum proposed by pupils

In previous tasks (1 to 6), the pupils examined what influences the pendulum movement. It is appropriate to formulate a general conclusion. Pupils should answer the initial research question about what characteristics of the pendulum affect its oscillation rate. When making a conclusion, they should refer to the data obtained from the investigations they have recorded in the tables for each task. Creating a justified conclusion belongs to the development of the idea of the science process and can be significantly influenced in this period.

Consequently, the teacher can create a situation that evokes the transfer of the gathered information. The taskof the pupils is to design a pendulum that will swing in the intended way, namely 30 oscillations per minute. Pupils should not create unsubstantiated guesswork in solving this task and solve the problem by trial and error (even if this is one of the solutions). It is preferable to focus the pupils on what results they have obtained in each of the tasks 1 – 6 and use these results to make a reasonable prediction. It may be that some of the pendulums that dealt with the tasks 1 to 6 were oscillating just as expected in the seventh task. At that time, it is sufficient to justify the result obtained from the solution of the given task. In principle, it is the development of the ability to „read“ the measured data and justify any other predictions.

Pupils are expected to design the weight, size, length, and triggering height of the pendulum based on the pendulum experience they have obtained during the previous investigations. They then verify their prediction by measuring the pendulum swing rate. If this is not confirmed, they adjust the pendulum to oscillate in the expected manner. When adjusting the pendulum, the teacher observes the pupils‘ variables on the pendulum. If they try to change something other than the length of the pendulum, he/she will suggest them that by solving previous tasks, they found that only the length of the string on which the weight was placed influenced the rate of oscillation.

After examining the pendulums (tasks 1-7), the teacher with the pupils discusses what causes the pendulum to swing. The aim is to realize that when the pendulum bob is triggered, it is attracted by gravity, but at the same time it is held by a fixed string, so it does not fall down but continues upwards. It is also important that children realize that Earth‘s gravity causes the pendulum to accelerate when it falls down. The same force – gravitational – causes the pendulum to decelerate smoothly as it moves up.

Tasks 8–15 

In Tasks 8–15, pupils explore different situations where objects are set into a motion by variously large forces acting in different directions with respect to the action of gravitational force. It is suitable to encourage pupils to discuss about the presence of a gravitational force, which acts constantly on the objects observed, always towards the center of the Earth. It is therefore appropriate that in each of these tasks, pupils record in the schematics of the observed situations the direction in which the force of gravity exerts on the object which they give in a certain force.

Since in each task pupils cause movement of objects (for example, shooting objects using sling-shots, catapult or air flow), the teacher also leads the pupils to try to indicate how the force exerted, which puts the object in motion, works and how gravitational force acts on the same object. In this way, the pupils‘ attention is drawn to realizing that the resulting movement of the object is not only due to the force we exerted, but also by the force of gravity. With regard to the thinking of children of this age, it is not yet to be expected that they will understand the folding of forces to which these activities create predisposing ideas. Therefore, it is not the task of the teacher to explain the observed phenomena in this context to the pupils. It is enough to focus the pupils‘ attention on the fact that each object, whether at rest or in motion, is objectto gravitational force.