Over the weekend, my students and I took a private tour of the Lick Observatory on Mount Hamilton. We got to see a couple different telescopes, hear about the research they’re involved in, and learned about the life of James Lick. Unfortunately, clouds were rolling in and the humidity was too high to use the big telescope for viewing (don’t want condensation on the optics). But I was able to set up my telescope (outside the dome in the photo above) so everyone got to see Saturn and Jupiter before we had to head down the mountain. It was actually pretty dark when the above photo was taken, that is the Milky Way appearing vertically by the dome and an airplane trail crossing over the dome. I highly recommend taking a fieldtrip to a local observatory if you have one in your area.
Instead of lecturing on the force of gravity this week, I had the high school students use a physics simulator at the Physics Classroom website to figure out for themselves how the force of gravity depends on the distance between objects and the mass of the objects. They have an activity sheet you can download that steps you through this activity. By moving the sliders you can change the mass of the moon and the planet, or you can move the moon closer or farther from the planet. This interactive works on smart phones and tablets as well as laptops.
Students set the masses and then recorded the Force at different distances. The handout does not require a graph, but I had them make a graph of their data. One student used a graphing calculator to do a best fit to his data and found that the force depends on 1 over the distance squared.
Students then kept the distance fixed and changed one of the masses and found that the force of gravity depends linearly on mass.
I also set up a demo that demonstrates how massive objects curve space-time by stretching a large piece of spandex-like fabric over a hula-hoop and then balancing it on chairs to keep it level. When a large marble is place in the center the fabric stretches and curves the fabric (space-time)
The larger the mass, the more the fabric is curved. Students took turns making smaller marbles orbit the large marble. We also increased the ‘mass’ of the ‘star’ in the middle by pulling down on it from below. I also talked about LIGO and how they’re measuring the vibrations on the fabric of space-time, which are gravitational waves. Here are videos on the subject.
Students were to read Chapter 5 Gravity in Foundation of Astronomy and watch the following Crash Course Astronomy this week.
We also did the How Do We Know What the Milky Way Looks Like? Activity from the Big History Project Unit 2 under Other Material. Since we can leave the Milky Way galaxy, the images that we see of it are not photographs but artists renderings based on what we can infer from our observations. Students were asked to pretend that they had never seen the outside of the building we were in and to write down a description of the house using only information they could gather from inside. They also had to write down what they could tell about about an ancient group of people from just a few photos of archeaological evidence.
The middle school class did the same activity sheet on gravity using the website but I started the class with a presentation on Newton’s Laws, the difference between speed and velocity, acceleration, forces and gravity. I skipped the presentation with the high school class since many of them had taken physics with me already. I did not require the middle school students to graph their data, but sketched the graphs on the white board. We also did the BHP How Do We Know What the Milky Way Looks Like? activity and played with the fabric of space-time.
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