Terminal velocity facts for kids

Terminal velocity is the speed an object reaches when it's falling through a fluid, like air, and stops getting faster. Imagine dropping a toy or a ball. At first, it speeds up. But eventually, it reaches a point where it can't go any faster. That's its terminal velocity.

This happens when two main forces become equal. One force is gravity, which pulls the object down. We call this the object's weight. The other force is air resistance, which pushes against the object as it falls. When the pull of gravity is exactly balanced by the push of air resistance, the object stops speeding up and falls at a steady rate.

Besides how heavy an object is, its terminal velocity also depends on its shape and how big its cross-sectional area is (how much of it faces the air as it falls). A flat, wide object will have more air resistance than a small, sleek one, even if they weigh the same.

How Does It Work?

When an object first starts to fall, gravity is the strongest force, so it speeds up. As it gets faster, the air resistance pushing against it also gets stronger. Think about sticking your hand out of a car window – the faster the car goes, the harder the air pushes on your hand.

Eventually, the air resistance becomes so strong that it perfectly matches the pull of gravity. At this point, the net force on the object is zero. Since there's no longer an unbalanced force, the object stops accelerating and continues to fall at a constant speed. This constant speed is the terminal velocity.

Examples in Real Life

A great example of terminal velocity is a skydiver. When a skydiver jumps out of a plane, they start to fall very fast.

Skydivers

A skydiver falling in a belly-to-earth (face down) position usually reaches a terminal velocity of about 195 km/h (122 mph). This is the fastest they will fall in that position.

It takes a little while to reach this speed. A skydiver might reach half of their terminal velocity in about 3 seconds. But it takes about 8 seconds to reach 90% of it, and even longer to get to 99%. This shows how the forces slowly balance out.

If a skydiver pulls in their arms and legs, making their body more streamlined, they can reduce air resistance. This allows them to fall faster. Their terminal velocity can increase to about 320 km/h (200 mph). This is almost as fast as a Peregrine falcon diving to catch its prey!

Images for kids

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  This graph shows the settling velocity (Ws) of a sand grain in water. It's similar to terminal velocity but in water instead of air.

See also

In Spanish: Velocidad límite para niños