Tuesday, November 10, 2009

Ok, back to my story: Last summer, my family spent the summer on a nice little island called Texel. We had a lot of seagulls there.On a "windless" day (yes I neglect air resistance), when my sister discovered open shells and a crowd of seagulls on the small patch of stone in the center of our garden, she asked me how the seagulls now, how to drop the shells to open them. Call me a bad brother, but I explained it like this:

"A seagull, dropping a shell on a stone, is a good example of projected motion. The key to this kind of motion is to seperate horizontal movement from vertical movement. Starting with horizontal movement, you have to remember Newton's laws (My sister is smart so she knows about Newton). According to this law, the shell will move horizontally with the same initial velocity the seagull flew with when it dropped the shell, until it is stopped by the stone it lands on."

Here my sister interrupted me:" So we can know how far the shell went from the point the bird dropped it, by stopping the time and multiplying it with the velocity the seagull flew with?" I really didn't expect her to understand Physics that well. "Yes exactly." I responded.

"But that's not all of it.The second part of the motion is vertical. Starting without an initial downward velocity it is important that we remember that gravity pulls the shell down with 9.8m/s^2 at all times. So the vertical motion is different from the horizontal motion, because it is accelerated. Knowing the time the acceleration and the initial vertical velocity (0), it is easy to determine the final velocity and the hight the seagull had when she dropped the shell."

"But how does the seagull know, how high to fly before they drop the stone?" my sister asked.
Yes, she really asked that. Unfortunately I had no idea. I really like physics but Biology is not my favourite subject."Mhhm, you know...." I started..."The birds have the final velocity they need to open the shells saved in the "how-to-open-a-shell" part of their brain, so they only need to apply their Physic rules, substitute their initial velocity and the final velocity, solving for the time, substitute time into the y-equation and solve for the hight.."
My sister still thinks seagulls are physics experts and calculate everything....am I a bad brother now?


  1. really good story, it really helps me understand the topic