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

Task 21

WORKSHEET Workshop

Materials and tools for a working group:

inclined planes (eg 50cm and 300cm boards), 2 identical toy trucks, load

The task is to determine whether the weight of a car affects how quickly it moves downhill. Thus, pupils will find out whether the heavier objects move on an inclined plane faster or slower. Partial task is to find out if this applies to any long boards. The heavier car is accelerating less than a lighter car due to the greater frictional force. However, it is also true that a heavier car accelerates more than a lighter car. Therefore, lighter car will reach the end of the board earlier. However, when we do the same observation on a long (equally inclined) board, the heavier car will overtake more easily and be the first end of the board. If we continue to observe cars, the heavier car will travel a greater distance, as it has increased momentum as it moves down the board.

After identifying the research question (Will the weight of the object affect the speed of its movement?), The teacher leads the pupils to make predictions, the first only for observation ona 50 cm long board. Pupils mark 1 and 2 with the appropriate boxes for those cars they think will be the first or the second. Subsequently, the teacher discusses the practical implementation of the verification with the pupils. In order not to measure the time (quite difficult to measure it appropriately exact way), they will create two equally inclined planes (it is advisable to incline the boards to less than 45 degrees to slow down the movement of the car and thus better register which one will be at the end of the board as first), on which both cars will run at the same time. It is very important to use the same cars, while one of them loads the load, the greater the better the difference in weight is. For this important moment, the teacher warns them to be aware of the planning of the verification.

After constructing inclined planes, pupils verify their predictions. It is very important to run the cars at the same time, so it is good if the carsare started by the same person who can better capture the same moment. It is necessary to repeat the observation several times, it is necessary to repeat it until the pupils perceive the observed result as proved, ie. they trust him. They record the observation result in the verification and evaluate the predictions.

While trying to answer the research question, the teacher asks pupils whether cars would behave the same if they were moving on a longer board. It leads pupils to create the conditions for moving cars on a three-meter board. After making predictions and justifying them, the teacher focuses on the design of the verification procedure. Although partly illustrated by the figure in the table in Task 21, it is only a scheme to which conditions need to be determined. For example, a teacher will point out that if we want to find out whether the length of the board affects whether heavy or light car will reach end of the board first, pupils should create a board that is equally inclined, only longer. He therefore suggests that the „slope“ (angle) of the board from the first part of the task be measured by their own gauge, which they created in the tenth task, and using the same gauge to adjust the three-meter board so that the angle is the same. They should thus obtain different long but equally oblique boards. The verification procedure will then be the same as in the first part of the task. The result of the verification will record and evaluate their predictions and then try to answer the research question. The answer to the research question and what the new one finds will conclude.