The moon and its gravitation
Through throw, throw the ball here…” shouted 12 year old Pratham, as he eagerly waited for his friends in the opposite team to throw the ball that he would catch. He always dreamt of becoming Yuvraj Singh, the best fielder a team can ever have, according to him. The ball was thrown and it took a projectile path before reaching him. But to everyone’s surprise, Pratham dropped it. He hardly ever dropped a catch!
He looked up at the sky and wondered if the ball had fallen too fast.
Soon, he heard his mother calling and had to go do his homework.
That night he was watching the space series that was going on, on one of the science TV channels. He was amazed to see the vastness of the earth, the dark space and the surface of the moon, full of craters. The commentary mentioned that the moon being smaller than the earth, the gravitational force was also six times smaller.
He saw astronauts jumping about on the moon, in slow motion. `Why are they jumping in slow motion,’ he asked his mother.
`That is not slow motion, it is real. They can jump like that because the gravity is very less there,’ she explained.
`What fun. If we played cricket on the moon, I would never lose a catch,’ said Pratham.
`What? Now switch off the TV and go to bed’, his mother ordered.
A few days later, some strangers came to his class and their class teacher introduced them as Education Specialists. “We will ask you a question. You can think about it for a while and then tell us whatever you think is the correct answer. The question is about the moon and its gravity”
The question was put up on the board.
If you are standing on the moon holding a pen, and you let it go, it will
- a) Float away
- b) Float where it is
- c) Fall to the ground
- d) Float towards the earth
(This question is a part of ASSET test, which is a diagnostic test for children. This question was put to around 3,668 students across the country. Only 15% of the students chose the Option C, which is the correct answer and 42% chose Option A, the most common wrong answer while 25.70% opted for Option B and 15.30% selected Option D.)
Pratham and his classmates Jia, Mansi, Manoj and Dhruv, got very excited. Pratham was sure he could answer this question, even before he heard the question.
Jia replied, “Of course it will fall down!”.
Dhruv responded, “I don’t agree with you that it will fall down. I think it will move towards the earth.”
After a moment of silence, Mansi said, “I think it will float where it is.”
Manoj did not agree. “I think it will float away in space,” he said.
The question baffled Pratham. If a man can jump on the moon, a pen should also fall on the ground. It was too simple an answer. There must be a catch somewhere. Wait, a man is heavy, a pen is very light. And if a man can jump in slow motion, a pen will practically float. But will it float away or will it stay where it is? But on earth, a pen will definitely fall on the ground. So maybe it will float towards the earth?
After thinking for five minutes, he was nowhere near the answer. Can you help Pratham find the correct answer? Can you understand where he may have gone wrong in his reasoning? We shall get deeper into the minds of students, including kids like Pratham and his friends. What goes on in their minds when they select particular options and the reasons behind those options will be dealt with in the latter half of the article.
How do children form misconceptions?
Misconceptions form in a variety of ways. Often misconceptions are passed on by one person to the other. In other cases, students may be presented with two correct concepts, but combine or confuse them. Sometimes students make, what to them seems like, a logical conclusion, but is simply drawn from too little evidence or lack of experience. The first step is to be aware of and diagnose students’ misconceptions.
`Have you understood?’ is a phrase often heard in classrooms. Students’ responses to this question tend to be mechanical as the question itself is perfunctory. Ensuring real understanding requires much more than just asking this routine question.
A matter of gravity
We discussed misconceptions students have about the concept of gravitation.
The students were asked the following question:
If you’re standing on the moon holding a pen, and you let it go, it will
- Float away
- Float where it is
- Fall to the ground
- Float towards the earth
(This question is a part of ASSET test, which is a diagnostic test for children. This question was asked to around 3668 students of class 6, across the country The correct answer is C, the pen will fall to the ground.)
Pratham was desperately trying to find an answer to the question. He wasn’t able to decide whether the pen will float towards the earth, float where it is or fall down. His instantaneous response was C; the pen will fall to the ground. But when he heard his friends choosing other options he was puzzled.
Some of you may be puzzled: Didn’t we learn all about the foundations of physics when in school? The answer is “yes” or “no,” depending on the interpretation.
The Educational Specialists who had gone to Pratham’s class were shocked to find children saying that the pen will not fall down. They tried to investigate the reason for the incorrect answers.
Dhruv, who said that the pen will float towards the Earth, had a very interesting reason to it. He said, “Just like Earth, even Moon has its gravity But the gravity of Earth is stronger than the Moon. So, just as a stronger magnet pulls things towards itself, even Earth will pull that pen towards itself because of its greater gravity”.
Manoj who said that the pen will float away in space, gave a reason that the Moon does not have any gravity and moreover, since there is no gravity in space, the pen can float away.
The Educational Specialists were totally bowled over by the reasons given by the students. They were surprised to find such reasons, and questioned children hoping to unearth more faulty reasoning among children. “Why do children think that the pen will float where it was let go?”
Mansi said the pen will float where it was “because it’s mass is very less.” The interviewer asked her, “So what will happen if I drop a heavy hammer on the moon?” She replied, “The moon has a weaker gravity as compared to Earth. But it will still fall down because it is heavy but the pen will not because it is lighter. They both will fall down only if dropped on Earth because Earth has a stronger gravity.”
Isn’t this interesting?
How do children respond in a situation they are unfamiliar with? How do they think in such a situation? What exactly goes on in the minds of students when they are faced with such a situation? These are some of the most challenging questions yet to be answered.
Research shows that when students face such a situation, they tend to answer based on the prior exposure they have had to the concept being asked. If the situation is completely new, as in the one that the students, in this case, faced, they try and relate it to a similar situation encountered before. The answer may not be totally correct scientifically. But they hold on to it because it satisfies all the criteria they have set in their mind and that fulfills their logical thirst. Any other answer and reason given that might contradict their logic would probably be considered as an error initially It is only when their own reasoning becomes contradictory that they are able to give up the incorrect reasoning and accept the correct scientific reason. This can happen only if wrong reasoning is investigated.
In this case, the very basic understanding of gravity seems to be missing that any two objects, whether they are on earth or anywhere in space, exert a force called gravity directly proportional to the product of their masses; however, it is inversely proportional to the square of the distance between them. In simple terms, as the distance increases, gravity decreases.
A common misunderstanding is that heavier things fall faster on earth than lighter ones because of their mass. But the scientific reason is that it is because of the difference in air resistance, and not the difference in mass! This misunderstanding may play a role in students choosing a wrong option in this question.
Students like Manoj do not seem to have grasped the basic understanding that any object that has mass exerts gravity. Students like Mansi seem to have partially understood the concept.
While students thinking like Dhruv probably try and relate gravity to magnetism and hence end up answering an option that seems to be logical to them but is scientifically incorrect.
Is teaching the right concept enough? Can we be sure that if Sir Isaac Newton himself came and taught this concept, the students would have been clear about the concept? The answer probably would be no! It is important to understand how students think, the reasoning they have so that the latter part of conveying the concept in an effective manner becomes simpler.