Thursday, November 21, 2019

gravity - Different density objects falling on Earth's atmosphere?


So I finally understood why 2 objects with different masses, free falling from the same distance reach Earth's surface at the same time (due to the objects Inertia). Now when the objects fall in the atmosphere (from what I understood) the parameters of the air resistance are, the speed and cross-sectional area of the objects. So let's say we throw 2 objects that are spherical and have the exact same volume (thus eliminating the cross-sectional area parameter) but different mass, making speed the only parameter of the air resistance. The heavier object (object A) will fall to the surface faster than the lighter one (object B) because its terminal velocity is higher.


So having all those things in mind my question is this: When dropping objects A and B at the same time (inside the atmosphere), will they fall at the same exact same speed UNTIL such time when object B reaches its maximum velocity?



Answer



No the denser sphere pulls away from the lighter sphere immediately. Just think about the instant they're both dropped and they fall some tiny amount of distance. They both run into the same amount of air molecules in the short distance but the net effect of those air molecules is less on the heavier of the two objects because it has more mass and therefor more momentum.


You don't have to wait until one of the objects reaches its terminal velocity. It's obvious which is denser just moments after they start falling.


No comments:

Post a Comment

classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

I am studying Statics and saw that: The moment of a force about a given axis (or Torque) is defined by the equation: $M_X = (\vec r \times \...