If an object is at rest, it will remains at rest, and if an object is already moving at a constant velocity, it will continue to move at that constant velocity.
Only if a resultant force is introduced, will this change. Only a resultant force can make a resting object move, or change the velocity of a moving object.
In other words:
A resultant force would be needed to:
move a resting object
change the velocity of a moving object
It is said that an object remains at rest (or continually moves at a constant velocity) because of
it's INERTIA.
An objects MASS indicates its INERTIA.
Larger masses have larger INERTIAS, making them more difficult to move.
Key points to remember.
Point 1
The resultant force equals to zero for:
a) objects that are at rest.
b) objects that are 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
Simple Questions
1. What is the size of the resultant force that acts on a resting object? zero
2. An object is moving at a constant velocity of 20ms-1.
2.1. What is the size of the resultant force that acts on this object? zero
2.2. What property of matter keeps the object moving? it's inertia
2.3. If the object never experiences a resultant force, will it eventually stop? No, it will never stop since a resultant force is the only property that can change the velocity and make it slow down to stop.
So without a resultant force, it could never possibly stop.