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Have you ever wondered why a feather falls slower than a bowling ball? Or how skydivers can safely land after jumping from thousands of feet in the air? The answer lies in understanding two key physics concepts: air resistance and terminal velocity.
Let's unravel this mystery with a thought experiment inspired by the brilliant Simone Giertz, a robotics enthusiast and YouTuber known for her quirky inventions.
Imagine you're holding two spheres of the exact same size. One is made of heavy iron, and the other is made of lighter wood. You climb aboard a plane and, with a daring spirit, decide to drop both spheres from a dizzying height.
Here's the riddle: Which sphere experiences greater air resistance once both reach terminal velocity?
Before we dive into the answer, let's break down the concepts at play.
Air Resistance: The Invisible Force
Air resistance, also known as drag, is a frictional force that objects encounter as they move through the air. Picture yourself walking into a strong headwind – you feel the air pushing against you, making it harder to move forward. The same principle applies to objects falling through the air.
Terminal Velocity: The Speed Limit of Freefall
When an object first starts falling, gravity pulls it downwards, causing it to accelerate. As the object gains speed, the force of air resistance pushing upwards also increases. Eventually, the upward force of air resistance becomes equal to the downward force of gravity. When this happens, the forces are balanced, and the object stops accelerating. It now falls at a constant speed known as its terminal velocity.
Solving the Riddle
Now back to our falling spheres. You might be tempted to think the heavier iron sphere experiences greater air resistance because it's heavier. However, here's the catch: both spheres have the same size and surface area, and we're assuming they have the same surface roughness.
Since air resistance depends on the object's shape and surface area, both spheres experience the same amount of air resistance at any given speed.
But here's where the difference in weight comes in. The heavier iron sphere has a greater force of gravity acting on it. To reach a terminal velocity where the upward force of air resistance equals the downward force of gravity, the iron sphere needs to be falling at a higher speed compared to the wooden sphere.
In Conclusion
While both spheres experience the same amount of air resistance at terminal velocity, the heavier sphere needs a higher terminal velocity to balance out the stronger gravitational force acting on it.
This riddle highlights how seemingly simple physics concepts can have counterintuitive answers. So, the next time you see a feather gracefully floating down or a skydiver expertly maneuvering through the air, you'll have a deeper appreciation for the invisible forces at play.
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