Answer 1:
Great question! I think the best way to tackle
this is by thinking about forces and
acceleration.
An object traveling through the air experiences
a force that will eventually control its distance.
We can separate the force on that object into
two parts.
The first force is gravity. This force
is directly proportional to mass: the more mass
the object has, the stronger the force of gravity
will be. Because of this, it turns out that
gravity does not matter when we compare
distance traveled by objects with different
masses.
The important part of the force is air
resistance, also called drag. The drag force
is proportional to the speed of the object,
because the faster the object is moving, the more
air molecules it will bump into, slowing it down.
But this force is not affected by the mass of
the object.
Now we want to know how the speed of the object
will be affected by the force. In physics, instead
of saying "the change to the speed," we usually
say accelerationit's the same idea. (Just
keep in mind that in our problem the acceleration
is negativeit's "deceleration.") To find
the object's acceleration, we take the force and
divide by the object's mass. This is known as
Newton's second law of motion, which we
usually write as F = ma (the force is
mass times acceleration).
So let's say we have two objects with the
same size but slightly different masses,
and we throw them at the same speed. Both objects
will feel a similar drag force, but the effects on
their speed will be different, according to a
= F/m. The heavy object will feel small
changes to its speed (its acceleration is close to
zero), while the light object will slow down a lot
(its acceleration is a large negative number).
In the end, the heavy object will travel
farther, since it was less affected by air
resistance.
Now that you've seen this example using
Newton's second law of motion, we can use a
"shortcut" for this kind of problem by thinking
about inertia. Inertia tells you how much an
object resists changes to its speed. The more
inertia it has, the more force it needs to speed
up or slow down. Newton's second law of motion
tells us that inertia is just mass. (Well, at
least in this case. There are different types of
inertia for dealing with changes to other types of
motion like rotation.)
If you try to test this in an experiment, there
is one more important thing to consider. If you
throw two objects "as hard as possible," it's
possible that you are applying the same force to
both objectsand as we talked about, that's
different from causing the same acceleration.
If you apply the same force to two objects, the
heavier object will end up being launched at a
lower speed because of its high inertia. To fix
this, you want to accelerate both objects for long
enough to get them to the same speed.
Best,
Click Here to return to the search form.
