Sunday, June 12, 2016

Bird bounces golf ball

This video showed up in my newsfeed this morning. How many cute puppy or click bait videos I watch is directly related to how early I hear, "Mommy, I awake. Come downstairs with me? Peas mommy?"

Apparently this was videotaped in Brazil on a golf course. The bird is a Brazilian Siriema and there are several opinions on why the bird does this to begin with in the comments:

"It thinks its an egg, its trying to crack it."

"No it just eats eggs, it thinks its a nut or a shell."

"See that hop? Its playing! My birds play like that."

Regardless of the reason, it's adorable. But it also demonstrates physics! Imagine that, physics works in Brazil, too. A Siriema can be 70-90 cm so its fairly tall. We can see the bird deliberately throw the ball down and it bounces higher than can be seen in the frame.

A standard American size golf ball (because there is a difference apparently) is 42 mm. You might be able to use the golf ball information to figure out the exact height of the bird. I attempted it roughly with paint but I do mean roughly since I ended up with about 0.5 meters. If anyone does a better job please let me know!

When I first watched it the sound was off—it disturbs "MickeyDonald" watching—but the sound is a great clue! In fact there is little audio except for the bounce. When I downloaded the video I got a video file and a corresponding audio file. I pulled the audio file into Audacity (my all time favorite FREE audio software) and selected just the bounce sequence. Luckily the very quiet golf course makes it easy to pick out those little bounces.

You can play the audio for students or use the original video to ask them to find the time of each bounce. If your students try to find the time visually they may include the time from the bird throwing the ball, the ball bouncing and then the ball returning. This would not be the proper time that the ball was in the air because it would include the ball's, albeit short, time from the bird's mouth to the ground.

I found the time from the first bounce to the second to be 1.55 seconds and the time between the second bounce and the third to be 1.25 seconds. Given this information alone students should be able to figure out how high the ball goes even though the whole bounce is not in the frame.

Taking the full time from bounce to bounce students know how long the ball was in the air which was the time up and down. If they divide 1.55 by two they will get the time to just go up or to just go down. I tend to lean towards thinking of the ball on the descent, falling from rest during that 0.775 seconds. Then it is easy to calculate d = (1/2)at2 based on that time and gravity at 9.814 or 10 m/s2 depending on your class level. Based on that I got that the ball reached a max height of an impressive 2.95 to 3 meters in the first bounce and 1.92 to 1.95 meters on the second.

What else can you do? Well, recall the height of the bird.

"If the bird were to drop it from its own height, less than a meter, would it have gone that high?" Hopefully your students say "No." (PGA regulations banned the use of Flubber in golf balls in 1961.)

"So why does it bounce so high?" Imagine an excited "oh, oh pick me!" from the back of your classroom. "The bird threw it down!"

You try to hide your pride and ask, "So what did the bird apply?" And you hear a resounding chorus of "A force!"

You can bring this discussion into energy:
  • If the 45.93-gram golf ball (yes they have strict standards) achieved that height, how much gravitational potential energy does it have at its max height?
  • How much work must the bird have done?
  • How much gravitational potential energy was lost between bounces?
  • Where did that energy go?
  • If you approximate the distance that the ball moved while the bird was applying that force (based on the height of the bird) how much force did the bird apply?
If you think of anything else to be learned or demonstrated from this video please let us know in the comments!

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