Why do you need to install application program/software in your computer?

Also called a "setup program" or "installer," it is software that prepares an application (software package) to run in the computer. Unless the application is a single function utility program, it is made up of many individual files that are often stored in several levels of folders in the user's computer.

Explanation:

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.