What is a Force? A force is a push or pull A force gives energy to an object, sometimes causing it to start moving (inertia), stop moving, or change direction. A spring scale is used to measure force. The unit of forces is a Newton (N)

What is Net Force? Usually, more than one force is acting on an object. The net force is the combination of all the forces acting on an object.

Calculating Net Force Forces applied in the same direction are ADDED together.

Forces applied in opposite directions are SUBTRACTED Forces applied in opposite directions are SUBTRACTED. (The smaller force is subtracted from larger force and direction of larger force is used)

Balanced and Unbalanced Forces When an object is not in motion, the forces are balanced (the forces acting on it are equal in all directions; a net force of 0 N) When an object is in motion, there are unbalanced forces acting on it (force in at least one direction is not the same as others). (A net force is not 0 N)

Two types of Forces 1. Gravitational—force of attraction between two objects; it’s dependent on the mass of the objects and the distance between them. The greater the mass of an object, the greater its force of gravity will be As the distance between two objects increases, the gravitational force decreases

Two types of Forces, continued 2. Frictional—a force that acts in the opposite direction of motion; friction must be overcome by a force.

3 Types of friction Sliding—solid objects slide over each other For example, sliding down park slide

Rolling friction—the use of wheels or bearings results in rolling friction. It is a lesser force than sliding friction. For example, roller blading on street

Fluid friction—gases and liquids offer resistance to moving objects Fluid friction—gases and liquids offer resistance to moving objects. This is also a lesser force than sliding friction. For example, swimming in ocean or racecar driving—air pushes against car