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

Task 8

WORKSHEET

Materials and tools for a working group:

sling, polystyrene ball, stopwatch

It is suitable to create a contextual situation for task 8. For example, a teacher with pupils can talk about how far they can throw a ball and what it depends on how far it will be shot. It focuses on the fact that someone can throw a ball very far, another, on the contrary, only relatively close. The aim is for pupils to try to identify the selected characteristics of the situation (variables) that could be reviewed later. For example, it can be argued that a light ball can be thrown further because we would need more strength for the hard. It is also important how we throw the ball, in which direction, etc. Subsequently, the teacher suggests that they should explore how the direction of throwing the ball affects how quickly and how far it will hit the ground. However, the teacher will inform the pupils that it is necessary to carry out the examination so that the pupils are sure that any differences were caused by a real change in the direction of throwing the balls. Even the same person fails to throw the ball in the same way, so he recommends throwing the balls with a sling.

To make the activity safe for children, it is suitable to shoot soft objects such as polystyrene balls or foam balls. Also, it is not appropriate if the activity is carried out in a small room, because even soft objects fired by a stronger sling-shot can hurt up close, so it is good to carry out activity in the gym, on the corridor or outdoors.

The teacher asks the pupils to look at the four different ways of firing a ball using a sling (Task 8). Their task will be to create an order in which they think the balls will fall to the ground. The goal is to find out which ball falls to the ground later. After the predictionsare made, the teacher discusses with the pupils how to carry out the activity. The time spans that the balls fall on can be measured using the stopwatch, but also by simple comparison. In the latter case, it is necessary to fire all the balls at once (four pupils at the same time make a beep). In any case, it is important to agree on how much the pupils will pull the slingshot so that some of the balls will gain more energy to move when fired.

The aim is to realize that if we act on the ball in the same direction as gravity, the ball‘s movement is the fastest. However, if we act in the opposite direction, the ball‘s movement slows down to zero and then accelerates backwards. This means that such a ball will fall at the latest. In order to realize this, the teacher leads them to sign the verification to indicate which direction the force of gravity exerts on the ball and to compare how it is related to the direction of action of the ball we are using with the sling. Consequently, the pupils formulate a conclusion in which they evaluate the direction in which the ball is to be applied in order to keep the ball in the air as long as possible.