Newton's first law of motion, also known as the law of inertia, states that an object at rest stays at rest, and an object in motion continues to move at a constant speed in a straight line unless acted upon by an unbalanced force. This means that objects behave predictably; they will not start moving or change their motion unless a force causes them to do so. For example, a ball will not roll off a table unless a force acts upon it, such as being kicked, and a moving object will not alter its speed or direction without an external force acting on it [2][3][5].

The law incorporates two key ideas: 
1. An object at rest cannot move unless a force is applied.
2. An object moving at a constant speed cannot change its speed or direction without an unbalanced force acting upon it [3][4]. 

In essence, this law signifies that forces need to be unbalanced in order to change an object's state of motion [1][5].

What is Newton's first law of motion?

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