Laws of Motion

Chapter three of Objects in Motion is Newton's Three Laws of Motion.  I collected several different demonstrations for this class, and thanks to The Happy Scientist, we demonstrated all three with a scale and some hand weights.

I created a worksheet so they could fill in all the different demonstrations we did during class.  I did a demonstration and then read from the book, did another demonstration, and so forth.

The First Law is that of inertia.  I placed a baseball card on top of a glass, and then stacked coins on top of the card.  I asked them to predict what would happen to the coins when I horizontally flicked the card away (they said the coins would fly off everywhere.)  Of course they dropped into the glass, and I let them try it a few times.  I also gave each of them some thick paper (bookmarks, actually) and a stack of pennies.  I instructed them to place the bookmark on the edge of the table so half of it was off of it and then to put a stack of coins on the bookmark.  They quickly pulled the bookmark out from under the coins and the stack remained intact on the table.  (The boys, of course, experimented with ways to make the coins spill...)

Another demonstration we did used a wheeled cart and a stuffed animal.  Shoving the cart made the toy fall off the back; stopping the cart suddenly made the toy fall forward.  We discussed the usefulness of seatbelts.

Finally, we wrapped up with The Happy Scientist: Newton's Laws that demonstrates all three laws in one activity.  You do not need a subscription to view this particular file, but I highly recommend it.  For $20 a year you get a wealth of videos, experiments, and science information.  Robert Krampf does a great job, and many of his videos are quite funny as well as interesting and informative.  All you need is a bathroom scale--the type with an analog display (digital won't work)--and a heavy object (hand weights work well.)  The kids are fascinated with how the scale changes as the weights are rapidly pushed up or pulled down.  Simple yet impressive!

Towers and Parachutes

Week 3 introduces us to the famous legend of Galileo dropping objects from the Tower of Pisa.  We completed the student exploration guide of the ExploreLearing Free Fall Tower Gizmo.  Another free tower simulator, Galileo Drops the Ball, and many other science simulators are available from SEED.

Before starting the Gizmo I gave a simple demonstration.  I took a feather and a ball and asked which would fall faster; then I dropped a small toy and a large toy.  Some were surprised that the second set of objects hit the ground simultaneously.  Next I dropped a book and a sheet of paper, and they fell at different rates.  Finally, I placed the sheet of paper on top of the book and dropped them; they fell at the same rate.  That got them thinking about concepts that they could explore further with the Gizmo.

After learning about air resistance, terminal velocity, and vacuums, I gave the 3 physics groups a challenge.  They each needed to build an egg parachute that met two criteria.  First, the egg had to fall without breaking; second it had to fall more slowly than a rock dropped simultaneously.

Each of the three groups were all successful, and had very different designs.  The older boys used a large sheet of newsprint for the parachute and a thick cardboard cone to hold the egg.  It's a good thing it didn't rain that day...

The girls covered fabric with lamination, adding in straw stays for the parachute and along the strings; they had a foam cube for the harness, decorated with flowers.  It fell the fasted of the three, but still slower than the rock.

The younger boys used a trash bag for a parachute and a cut up egg carton for the harness, with a good amount of duct tape to hold it all together.

I gave them two weeks for construction.  The day of the drop was very windy.  All the kids (21 of them) gathered for the event.  You can see the videos of each parachute being dropped out a window, a team member dropping the parachute and an adult dropping a rock.

Pendulums

Our third week of co-op we performed the pendulum experiment described in the book.  We had three fishing weights (labeled 1, 2, and 3), three lengths of string, and a stopwatch. I created a data sheet (link goes to Google Docs) for them to fill in; they will need three of them to record data for the entire experiment.

This is one experiment in which the kids are very much surprised by the results.  They expected that lifting the weight higher up would increase the time for 10 swings; they also expected a heavier weight to make a difference.  Only the length of the string matters.

Related Gizmos:  Period of a Pendulum and Pendulum Clock

Ellipses

We are working our way through Objects in Motion: Principles in Classical Mechanics by Paul Fleisher. The first lesson is about Kepler's Laws of Planetary Motion.

A key moment for Kepler was when he abandoned circular orbits for elliptical ones, so I designed an activity around ellipses.  I cut a large foam board into quarters, one for each student, and tacked paper to it.  They put two push pins along the horizontal midline of the paper, slipped a string with the ends tied together over it, and drew an ellipse by drawing the string taut with a pencil and circling the push pins.  They moved the pins progressively farther, then closer, and observed what happened to the ellipse.  We discussed how a circle is a special form of an ellipse, just as a square is a special form of a rectangle.

I then discussed Kepler's Second Law and shaded in a pie piece away from the sun and close to the sun.

For the elementary group we skipped the third law.  For the middle school kids I simply wrote the formula and we discussed what it meant, including exponents and proportionality.  They got the fact that distant planets orbit more slowly and related that to the force of gravity.

If you use ExploreLearning Gizmos like we do, there's one on Ellipse and another on Kepler's Laws.

Discount for Upcoming Live Online Immunity Class

I will be teaching a six-week class on the immune system for high school students called Immunity in Sickness and in Health.  The class runs from January 17th until February 21st, Mondays from 1:30 to 2:30 live over the Internet.  All you need is a computer, headphones, and a microphone.  The course costs $90, with a $15 discount for early registration if you register before November 1st.