Newtons First Law

In other words :
A resultant force would be needed to move a resting object.
An object moving at constant velocity remains moving at THAT constant velocity.
Resting objects remain at rest because of a property of matter called INERTIA.
INERTIA is also responsible for maintaining an objects constant velocity.

Key points to remember.
Point 1
The resultant force equals to zero :
a) for objects that are at rest.
b) for objects moving at a constant velocity.

Point 2
If an object is at rest, or if it is moving at a constant velocity:
a) thus the resultant force equals zero.
b) balanced forces act on the object

Point 3
Inertia is the property of matter that:
a) keeps resting objects at rest
b) keeps an object moving at its constant velocity

Example
A bus is being driven with 50 passengers at a constant velocity of 60km/h.
One of the passengers is standing, What happens?

…thinking… There are 52 things moving : the bus, the driver, and 50 passengers. All 52 things are moving at 60km/h and this velocity will be maintained by their individual “inertias”. That’s what inertia does; it maintains constant velocities!

Answer
The bus: The bus slows down because it receives a resultant force (it has brakes).
The Driver: The driver slows down because he receives a resultant force by his seatbelt.
The Seated Passengers: The 49 seated passengers slow down because each receive a resultant force (they would put their arms forward to the seat in front)

The above 51 objects each received a resultant force, that then affected their inertia.

The Standing Passenger: The single standing passenger would not receive a resultant force. His inertia is thus unaffected, and he would continue moving forward at 60km/h as a result of this inertia. Since the bus and other passengers are all now slower, he would fall forward. Oops!