Answer 1:
Sounds like an interesting research problem. Like
for many problems, there is a lot of information
you can draw from, but it's difficult to figure
out how to apply it. I still think it's worth
trying! Here's my attempt.
A useful way to think about this problem is in
terms of elasticity of the collision between the
ball and the ground. In a perfectly elastic
collision, the ball collides with the ground
and bounces off with as much momentum as possible.
In this kind of collision, the ball loses no
energy, so no sound is made and no heat is
generated. If you let the ball continue to bounce
in a perfectly elastic way, it will never stop
bouncing. (This is not practical: any collision I
know how to set up is not perfectly elastic.)
The opposite situation is a perfectly inelastic
collision. In this case, the ball collides
with the ground and loses all of its momentum and
all of its kinetic energy. All of that energy is
converted into heat or soundusually both.
Imagine dropping a cannonball on the grass: you
end up with zero bounces and a lot of noise.
You found that the collision between the soccer
ball and natural grass field is more elastic than
the collision between the soccer ball and turf
field. Why? The difference must come from
the ground surface, so let's think about what
factors can affect elasticity. Maybe the dirt
below the natural grass plays a role, or the under
layer below the turf (often rubble or gravel).
We could test how many times a soccer ball bounces
on similar dirt or similar gravel and see if that
lines up with the grass surfaces. I would also
consider the arrangement and texture of the grass.
Think about how corrugated cardboard is stronger
than flat sheets. The way that the grass weaves
together (or doesn't weave together) might affect
the elasticity.
