What is inertia used for?
Inertia is not really a tool to be used...
Inertia is basically an object's resistance to being moved. It
stems from Newton's 2nd law of motion, which states that the net
force on an object is equal to it's mass multiplied by its
acceleration. Fnet=ma. So, the larger the mass of the object, the
more force is required to accelerate it.
To actually answer the question completely, we have to consider
every situation in which an object has a net force on it, and so
you really can't do that because it happens every day, every where,
on virtually everything. Consequently, I'll provide a couple of
examples instead...
Inertia is used for ice skating... Inertia is the reason that an
ice skater can glide long distances across the ice without pushing
off. This is because the friction force of the ice (which is trying
to stop her) is not high enough to make her mass decelerate.
Inertia is used to annoy shoppers pushing shopping carts... When
you push the shopping cart, you apply a force to it. The heavier
the cart, the harder it is to get moving. Inertia describes the
reason a heavier cart is harder to move.