Does a heavier object fall faster to the ground, than a lighter object? Well, one would have thought that this question had been settled with Galileo’s famous experiment at the Tower of Pisa, but looks like it’s not quite the case. What do you think would happen if you place a sheet of paper on top of a book you are holding, and drop the book? Do you expect them to fall together, or do you expect the paper to ‘stay back’ and fall slower to the ground? Answer this question, and verify your answer by actually trying this out before you read further… what did you find? surprised?
I have tried this with several students, teachers and intelligent adults over the years, and most are surprised at what they see. Why do we continue to believe that heavier objects fall faster than lighter objects, even though we might have read that they fall at the same rate or even solved many problems using equations that show they do? This probably happens because we do not grasp the idea of air resistance- air being invisible, seeing the slow drifting fall of a leaf or a feather, we may interpret such experiences to form the idea that ‘lighter objects fall slower.Even if we understand the idea of air resistance (which most older children or adults do), we may still be wrongly extrapolating the idea that heavier objects experience a higher gravitational pull to conclude that they would also fall at a faster rate. It is quite ‘intuitive’ to think that a heavier object will fall faster than a lighter object and not entirely wrong- it is just a limited idea that applies only in special cases.
Check out this 1.5 minute clip of a conversation between grade 8 students- you can see that it’s not easy to understand why an object is falling faster if it’s mass has not increased- till you start understanding the idea of air resistance. A lot of learning or teaching science well is about challenging our incorrect intuitive notions, and replacing them with proper scientific ideas.
So how could one challenge one’s incorrect ideas? One approach is through careful observation. Drop a heavy brick and a tightly crumpled paper ball at the same time from the top of your school building and check when these reach the ground. (Make sure of course that there is nobody around- inform your teacher and others about this experiment so that everyone can witness what happens, and importantly remain safe out of the path of these objects :-)).
But does that 1% doubt still linger in your mind about whether a feather would reach the ground at the same time as a heavy bowling ball? What would it take to be 100% sure- only way is to drop these objects in a vacuum environment- where would you find one! Fortunately for us, this expensive experiment has been done- watch the amazing clip below from BBC’s Human Universe series.
Wasn’t that amazing?
At the end of the clip though, we are told that Einstein would say that the ball and feather are actually not falling or moving at all! How crazy is that! Check out this clip from PBS Nova on Gravity- Newton vs Einstein. If you are still in school though, it is unlikely that this is going to be on your test, as most adults with a technical/ scientific background and many science teachers (just like me) would still struggle to understand this ‘space-time’ fabric stuff. Keep in mind that reality (what happens) is what it is- beautiful and complex, and as science tries to find explanations and underlying rules for how the world works, we keep improving our explanations (scientists call these ‘models’). Hopefully our models keep getting better with time, but they are still an approximation to reality…