Balanced & Unbalanced Forces (AQA GCSE Physics): Revision Notes
📚 Revision Notes
5.1.8 Balanced & Unbalanced Forces
Balanced Forces
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Balanced forces occur when two or more forces acting on an object are equal in size but opposite in direction. As a result, the net force on the object is zero, and there is no change in the object's motion.
Key Points:
- No Acceleration: When forces are balanced, the object remains at rest if it was initially at rest, or continues to move at a constant velocity if it was already in motion.
- Equilibrium: The object is said to be in equilibrium.
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Example:
- Stationary Object: A book resting on a table experiences balanced forces. The gravitational force pulling the book downward is balanced by the normal force exerted by the table pushing the book upward.
- Constant Velocity: A car moving at a constant speed on a straight, level road has balanced forces if the driving force from the engine equals the resistive forces (e.g., friction and air resistance).
Unbalanced Forces
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Unbalanced forces occur when the forces acting on an object are not equal in size or not opposite in direction. This results in a net force that causes a change in the object's motion.
Key Points:
- Acceleration: When forces are unbalanced, the object will accelerate in the direction of the net force. This means the object will speed up, slow down, or change direction.
- Change in Motion: The object is not in equilibrium and will experience a change in velocity.
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Example:
- Accelerating Car: When a car speeds up, the driving force from the engine is greater than the resistive forces. This unbalanced force causes the car to accelerate.
- Falling Object: An object dropped from a height experiences unbalanced forces due to gravity pulling it downward, while air resistance acts in the opposite direction. If the object is in free fall, gravity is the dominant force causing acceleration.