Newton's First and Second Laws

This lesson covers inertia, the equation F = ma, and balanced and unbalanced forces, as required by the Edexcel GCSE Combined Science specification (1SC0). Newton's laws are the foundation for understanding how forces affect motion.

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Newton's First Law

Newton's First Law states: An object at rest will remain at rest, and an object in motion will continue to move at a constant velocity, unless acted upon by a resultant force.

In simpler terms:

• If the resultant force on an object is zero, it stays still or keeps moving at the same speed in the same direction.
• If the resultant force is not zero, the object will accelerate (change velocity).

Examples

A book on a table: The weight of the book acts downward and the normal contact force acts upward. These forces are balanced (resultant = 0 N), so the book stays at rest.

A car at constant speed on a straight road: The driving force equals friction plus air resistance. The resultant force is zero, so the car continues at constant velocity.