1. Balanced and unbalanced
By: Francisco, Raissa

2. Net force
net force is the overall force acting on an object. In order to calculate the net force, the body is isolated and interactions with the environment or other constraints are represented as forces and torques in a free-body diagram.

3. friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
There are several types of friction:
Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction "stiction" between non-moving surfaces, and kinetic friction between moving surfaces.
Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other.
Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces.
Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

4. Inertia
Inertia is the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction or state of rest. It is the tendency of objects to keep moving in a straight line at constant velocity.

5. gravity
Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including planets, stars and galaxies.