Why do maple tree seeds spin as they fall?
One of many people’s favorite nature walk memories, is watching or playing with spinning maple tree seeds. But, have you ever wondered why they spin? In this tutorial, we are going to look at the science behind why maple seeds spin – and the reasons why they need to spin. Are you ready? Lets get started!
What are maple seeds?
Before we explore how and why maple seeds spin, it will be nice to take a minute and think about what a maple seed is. A maple seed is a type of seed known as a samara, or helicopter seed – a seed that flies with wings. And, it comes from the maple tree. It is not the only type of flying tree seed, but is the one I will focus on here.
What does a maple seed look like?
If we take a closer look at a maple seed, we will start to notice some interesting features. See if you can find one to examine. When you pick it up, you should notice that it is made up of a heavy ‘seed’ at one end of a long, thin wing. And, if you look even closer, you should notice that one side of its wing is thicker, smoother and rounder, while the other side is thinner, rougher or jagged
Why do maple seeds spin?
If you try to balance it on your finger, you should notice that the heaviest part of the seed – the ‘seed’ bit, is right at one end of the seed, meaning its center of gravity is somewhere near the middle of the seed (wing). This combination of wing structure and center of gravity is what makes a maple seed spin.
If you drop your maple seed, you should notice that it always falls with the heavier ‘seed’ at the bottom and the lighter wing at the top. This makes sense, since the seed is their heaviest point. And if you look even more closely, you should start to notice that your seed always spins in the direction of its smoother, rounder, thicker edge. But, why?
Maple seeds make mini torpedoes!
To answer this question, some clever scientists decided to run an experiment and see if they could find out. So, they dropped their maple seeds down into oil and air, and recorded the air flow around the seeds and their movements as they fell. Their results were pretty amazing. As every seed fell, it made its own mini tornado! It is all down to three factors: gravity, drag and resistance.
Gravity always pulls the heavy end (the seed) downwards, while drag (wind resistance) is greatest on its widest area – the wing. This pushes the wing upwards, so it acts like a parachute and slows the samara’s fall. Finally, air flow over the surface of the samara changes between the rough and smooth edges of the wing – over the rough edge, there is a lot of turbulence, while the smooth, rounded edge has less resistance.
This difference in resistance, directs the flow of air above the seed, creating a spiral or vortex of air above the falling seed. This spiral of air makes the samara spin in the shape of a mini tornado narrow end towards the seed and wide end towards the wing – spinning the seed as it falls.
But, why do seeds need to spin?
So, we now know how maple seeds spin, but have you ever wondered why they need to spin? What’s the point of spinning when they could just fall straight down, instead? It is all down to competition and survival.
Let’s recap a few maple seed facts: They have wings; they spin as they fly; their wings act as parachutes, slowing them as they fall. So, what does this mean? It means that the maple tree has evolved to help its seeds get as far away from the tree as possible.
First, by acting as a parachute, the speed at which the seed falls, is slowed down, making it stay longer in the air, giving it a longer time in the air, and a bigger gap in which to catch the wind. Then, the wings act like sails, helping the wind blow the seed further away. Lastly, spinning like a helicopter, helps the seed stay aloft even longer, giving the seed time to blow even further away.
Seeds fly for survival
But, why should this all matter? Why is blowing so far away important for the seed? The answer is a matter of survival and evolution. If the seeds plopped straight down beneath their trees, they would end up competing for sunlight, water and minerals. There is also a risk of cross pollination. Whereas, the seeds that manage to get away and find their own space to grow, can grow stronger and bigger – because they are no longer in competition with their parents!
Well… there we go! A quick overview about why maple seeds spin as they fall. I hope you enjoyed this tutorial? Let me know in the comments. Happy nature walking and see you soon!
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