Gravity, Air Resistance, and Friction
A falling object experiences gravity's pull, creating a force equal to its mass × gravitational acceleration 9.81m/s2. For a 14 kg bowling ball, this force is -137.2 N (negative because it points downward).
Air resistance opposes motion through air, acting in the direction opposite to travel. When a falling bowling ball experiences 45 N of air resistance, the net force reduces to -92.2 N, slowing its acceleration.
At terminal velocity, air resistance perfectly balances the weight of the object. For our bowling ball, air resistance would equal 137.2 N upward, resulting in zero net force and constant velocity.
Pro tip: Friction always acts in the direction opposite to motion or potential motion. There's a big difference between static friction (before movement starts) and kinetic friction (during movement).
Friction comes in two types: static friction acts on stationary objects resisting movement, while kinetic friction acts on objects already in motion. Both types depend on the normal force and a coefficient of friction specific to the surfaces in contact.