The past two weeks have been ridiciously busy. My eldest son and I worked the Livermore Airport Open House all day one Saturday – telling kids about rocks, fossils and lapidary while watching pilots do acrobatics with their airplanes. The next morning we got up EARLY to catch a flight to Portland and spent all of Monday at Discover Reed College, flying home late Monday night. I had never been to Oregon before and it was beautiful. We were both struck by how green Portland was. There are only two seasons where we live, brown (hot, dry summers) and green (if we’re lucky and actually get our rainy season). Unfortunately we also happened to see the wildfires in California as we flew directly over them on our way home.
This past weekend I taught a 4-H Archery Leader course, teaching other adults and teens how to teach archery. This is always a lot of fun because the people are great and we spend most of the weekend outside at the archery range. In the picture below the teen in green is teaching the other, my younger son (who is pretending he doesn’t already know archery) proper shooting form with a piece of elastic. Note the brown hills as mentioned earlier – I’m ready for rain!
Since I’ve been so busy I didn’t have a lot of time to prepare for class today and when I woke up to the news from LIGO I decided we would do some current events at the beginning of class. I showed the following two videos and had a lot of discussion with the students on what it meant and why its so cool.
Next week the class is actually going on a fieldtrip to iFly so we spent the rest of class calculating our own terminal velocities (this was an activity that iFly provided us). When you jump from a plane you do NOT accelerate forever, at some point the force of air resistance becomes large enough to cancel out the force of gravity (your weight) so that the total force on you is zero. If the total force is zero, then your acceleration is zero and you fall at a constant velocity. We talked about different factors that contribute to the force of air resistance – the density of air, your speed (think about walking versus running in deep water) and your area – if you spread out your body as you fall the air will resist your movement with a great force than if you move your body into a streamlined position. There’s also a drag coefficient which depends on your shape. Students estimated their surface area by assuming their body was made of a series of rectangles and ellipses, measured the length and width of each rectangle, calculated the area and added them up. Students also had to find their mass in kg. I have a scale with a switch on the bottom to change the units from pounds to kg so students were able to measure their mass in kg. Most found they had a terminal velocity of around 40 m/s or roughly 90 mph. Next week when they are at iFly they will find out if their estimates were correct.
Here’s a website that steps you through some calculations for terminal velocity,