|Do heavier objects fall in less time?
|Question Date: 2016-02-16|
The simplest answer is: no, an object's weight
usually will not change its falling speed. For
example, you can test this by dropping a bowling
ball and a basketball from the same height at the
same time--they should fall at the same speed and
land at the same time.
But that's not always true if there is a lot of
drag such as air resistance. Air resistance
happens because objects bump into lots of air
molecules as they fall. The air molecules get
knocked away and take some of the kinetic energy
away from the object, which makes the object slow
down. For example, if you drop a styrofoam cup and
a metal cup the same way, the metal cup might
reach the ground first. This is because the weight
of the metal cup gives it more inertia, which
makes forces like drag affect it less.
Sometimes, people will use their knowledge of air
resistance to make things move faster or slower.
Parachutes are designed to have a lot of air
resistance and fall as slow as possible. On the
other hand, the noses of planes are designed to
"cut through the air," which is a way of saying
they have low air resistance.
In physics, no - all objects fall at exactly
the same rate. However, air slows down falling
objects, so on Earth (or any planet with an
atmosphere) a heavier object will reach the ground
in less time. To see what happens to falling
objects without air, watch this video:
In real life, heavier objects sometimes fall
faster than light objects, but not because of
gravity. Gravity makes all objects increase
their speed at the same rate, regardless of how
big they are. But if you drop 2 things
outside, the air molecules may slow down one thing
more than another.
For instance, a rock will be slowed down less
by the air molecules than a feather because of
their different shapes. But if you drop a rock and
a feather in a vacuum, which is somewhere without
any air, then they will fall at the same exact
speed. The experiment of dropping things in a
vacuum has actually been done and it has shown
that they objects do fall at the same rate.
Some times. In the absence of air resistance,
all objects will accelerate towards the source of
gravity with the same rate. This was nicely
demonstrated on the moon when an astronaut dropped
a feather and a hammer, and they both took the
same time to fall towards the surface of the moon.
On Earth, there is much more atmosphere than on
the moon (which is very convenient for sustaining
life, I might add), so air resistance becomes
important in some cases. For objects with very low
density or with very high surface area (such as a
feather, or a kite), the air might exert a strong
enough force to slow the descent of an object, or
even lift it up if the wind is blowing strongly
enough. (Things like dust can stay floating for a
long time if the particles are small enough.)
So, if you're on Earth where objects are
falling through air, a heavier object may fall
faster than a similarly-sized lighter object, but
it usually won't be noticeable to us because the
effect is often quite small for most things we
deal with in practice. (That is to say, bigger
than a tennis ball, and falling from a height of
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