text: 1. gravity is acting straight down, centrifugal force is acting towards the wall, and friction is holding her against the wall.  Obviously the centrifugal force and friction together are stronger than the gravity, or she would fall.\n\n2. The book was "at rest" -- an object tends to stay at rest unless acted on by an external force (that's inertia).  The book's mass (weight) gave it enough inertia to overcome the friction with the dashboard, so when the car moved the book didn't move with it, but tried to stay where it was.\n\n3. the surface area of the skydiver before opening the parachute doesn't offer much air resistance, so the skydiver is mostly being acted on by gravity and reaches terminal velocity fairly quickly.  Once the parachute is opened, the surface area of the skydiver/parachute combination is many times greater than it was, greatly increasing air resistance -- which slows the acceleration due to gravity enough to allow the skydiver to make a soft landing.\n\n:)