Define and explain terminal velocity.

Terminal velocity is the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.

In more detail, terminal velocity is a concept in physics that describes the maximum constant speed that a falling object reaches when the force of gravity pulling it downwards is equal to the drag force acting upwards on it. This happens when the object is no longer accelerating and is falling at a steady speed.

When an object first starts falling, it accelerates due to gravity. However, as its speed increases, the air resistance (or drag) acting against it also increases. At a certain point, this drag force equals the gravitational force acting on the object. When these two forces are balanced, the object stops accelerating and continues to fall at a constant speed. This speed is what we call the terminal velocity.

The value of terminal velocity depends on several factors. These include the mass of the falling object, its surface area, its shape, and the density of the fluid it's falling through. For example, a small, dense object like a steel ball will have a higher terminal velocity than a large, light object like a feather. Similarly, an object falling through air will reach a lower terminal velocity than the same object falling through a denser medium like water.

In the real world, terminal velocity is an important concept in a variety of fields. For instance, it's crucial in understanding how parachutes work. When a parachute opens, it greatly increases the surface area of the falling object (the parachutist), which increases the drag force and reduces the terminal velocity to a safe level. Similarly, animals like squirrels and certain types of spiders can glide or 'fall with style' thanks to their body shape, which allows them to reach a low terminal velocity and land safely.

In conclusion, terminal velocity is a fundamental concept in physics that describes the maximum constant speed that a falling object can reach. It's determined by a balance of forces and depends on several factors, including the properties of the falling object and the medium it's falling through.