4.1

• An object reaches terminal velocity when the force due to air resistance acting on it is equal to the force of gravity. At this point, the falling object reaches a maximum falling speed. The net force on the object is zero.
• Gravitational field strength is the force per unit mass

  g = 9.8 N /Kg
• Mass is the quantity of matter in an object. The only way to change mass is to add or remove matter.
• Weight is a measure of the force of gravity, Fg, acting on an object. Weight is a vector quantity, and its magnitude is measured in Newtons (N).