A prime example of balanced forces acting on a moving object is reaching terminal velocity.
Understanding Balanced Forces
In physics, balanced forces are two or more forces applied to an object that cancel each other out. When forces are balanced, the net force on the object is zero.
- Key Point: While balanced forces result in zero net force, this does not necessarily mean the object is stationary. According to Newton's First Law of Motion, an object experiencing zero net force will either remain at rest or continue moving at a constant velocity (constant speed in a straight line).
Terminal Velocity Explained
Consider an object falling through a fluid, such as air or water. Initially, the main force acting on it is gravity, pulling it downwards. As the object accelerates, it encounters a resistance force from the fluid, known as drag (or air resistance in the case of air). The drag force opposes the motion and increases with the object's speed.
As the falling object's speed increases, the drag force also increases. Eventually, the drag force becomes equal in magnitude and opposite in direction to the force of gravity.
According to the reference provided: "Terminal velocity is a good example of balanced force because the gravitational force and the air resistance balance each other. The terminal velocity is reached when the force of gravity is equal to the drag force on an object."
At this point, the net force on the object becomes zero.
Why Terminal Velocity is an Example
Even though the forces are balanced (gravity down, drag up), the object is still moving. Since the net force is zero, the object stops accelerating and continues to fall at a constant speed – this constant speed is called terminal velocity.
Here’s a simple breakdown:
| Force | Magnitude at Start of Fall | Magnitude as Speed Increases | Magnitude at Terminal Velocity |
|---|---|---|---|
| Gravity (Weight) | Constant | Constant | Constant |
| Drag (Air Resistance) | Low | Increases | Equal to Gravity |
| Net Force | High (downward) | Decreases | Zero |
| Motion | Accelerating (speeding up) | Accelerating (slowing rate) | Constant Velocity |
This scenario perfectly illustrates how balanced forces can act on a moving object, maintaining its motion without causing further acceleration.
For instance, a skydiver falling through the air reaches terminal velocity when the upward force of air resistance matches the downward force of gravity. They continue to fall, but their speed no longer increases.
