* Net Force: When multiple forces act on an object, we consider the *net force*. This is the overall effect of all the forces combined.
* Equilibrium: If the net force is zero, the object is in equilibrium. This means:
* Static Equilibrium: The object is stationary (not moving).
* Dynamic Equilibrium: The object is moving at a constant velocity (unchanging speed and direction).
How Forces Cancel:
* Equal and Opposite: The most common way for forces to cancel is when they have the same magnitude (strength) but act in opposite directions. Think of a tug-of-war – if both teams pull with equal force, the rope doesn't move.
* Vectors: Forces are represented by vectors – they have both magnitude and direction. When forces are not directly opposite, we need to consider their angles to see if they cancel. We can use vector addition to determine the net force.
Examples:
* A book on a table: The force of gravity pulling the book down is balanced by the normal force from the table pushing upward.
* A skydiver reaching terminal velocity: The force of gravity pulling the skydiver down is balanced by the force of air resistance pushing upward.
* A car moving at a constant speed: The engine's forward force is balanced by friction and air resistance.
Key Points:
* Equilibrium doesn't mean no forces are acting, it means the forces are balanced.
* If forces are unbalanced, the object will accelerate (change its speed or direction).
