Overview
This lecture introduces Newton’s First Law of Motion, explaining how the motion of objects is affected by balanced and unbalanced forces.
Newton’s First Law of Motion
- Newton’s First Law states: A stationary object with zero resultant force remains stationary.
- A moving object with zero resultant force continues moving at the same velocity (same speed and direction).
- Velocity changes only if a resultant force acts on the object.
Resultant Forces and Motion
- If all forces on an object are balanced (resultant force is zero), motion does not change.
- For a stationary object: balanced forces mean it stays still.
- For a moving object: balanced forces mean it keeps moving at the same velocity.
Examples of Balanced Forces
- Two equal and opposite forces (e.g., 50 N right and 50 N left) result in no change in motion.
- A moving car at constant speed has the driving force balanced by resistive forces (like friction).
Unbalanced Forces and Changes in Motion
- A non-zero resultant force causes acceleration (change in speed or direction).
- Stationary object + resultant force = accelerates in the force’s direction.
- Moving object + resultant force in opposite direction = decelerates (slows down).
- Resultant force can also change the direction of an object’s motion.
Key Terms & Definitions
- Resultant Force — The total force acting on an object after all forces are combined.
- Velocity — The speed of an object in a given direction.
- Resistive Forces — Forces that oppose motion (e.g., friction).
Action Items / Next Steps
- Review Newton’s First Law in your revision workbook.
- Practice with example questions on Newton’s First Law.