Chapter 3 Lab #7:
Using collisions, students will demonstrate Newton’s first law of motion.
Chapter 3 Lab #7:
Using collisions, students will demonstrate Newton’s first law of motion.
As many of you know, the Learning Cycle is an approach to science instruction developed by Atkin and Karplus in 1962 while working on the SCIS (Science Curriculum Improvement Study) project. This approach puts the phenomena first. Names and numbers are brought into the picture only after students are allowed direct contact with the phenomena. Although there are a number of variations on the theme, the essential learning cycle consists of three phases. These phases include exploration, concept development and application. The “Learning Cycle” method may be used to teach virtually any topic in physics and that includes Newton’s Laws. The forces exploration consists of a “smorgasbord” of twelve activities relating to Newtons laws. This exploratory’s emphasis is on the introduction of Newton’s 1st, 2nd and 3rd laws. At each station students are asked to perform one or more activities and answer questions based on their observations. These stations use a variety of manipulatives. Some stations feature common household items; others use either commercial devices or teacher-produced apparatus. I would like to share some of our students’ favorite stations with you. During the last 30 years, Dr. James Hicks and I have assembled exploratory activities that we’ve used to introduce each major topic (for example, forces, energy, optics, wave phenomena, electricity, magnetism, etc.) in our physics classes. These collections contain both time-honored “experiments” and activities that Jim and I have concocted or borrowed from our students or other teachers.
Here are some guidelines for the “Newton Adventure”:
Newton’s 1st law (a.k.a., Galileo’s Law of Inertia.)
Not with my dishes you don’t!
Haven’t you always wanted to try the old table cloth and dishes trick? To perform this time-honored magician’s trick, place some old dishes (you may want to begin with a single plate) on a smooth tablecloth. Grab both ends of the tablecloth and, without hesitation, pull the tablecloth out from under the dishes as quickly as you can.
The Physics Van Outreach program http://van.hep.uiuc.edu
Tee off time…
Balance an embroidery hoop on the mouth of an empty flask or glass soda or catsup bottle (see photo). Now place an inverted golf tee on the top of the hoop. Note: a piece of chalk with a flat bottom also works well. Make certain that the tee is directly over the mouth of the bottle. Now take a deep breath, and remove the hoop by quickly grabbing the inside center of the hoop.
i) What happened to the tee?
ii) Why did the tee drop into the container?
iii) Repeat the experiment, this time quickly grab the outside of the hoop. What happens now? Can you explain your observation? That is, why does the tee only fall straight down when the hoop is grabbed on the inside?
Bend a stiff piece of wire, such as a coat hanger, into the shape shown in the figure. Using two sticks of modeling clay, fashion two spheres of clay around each end of the wire. Balance the center point of the wire on the top of your head. Make certain that the wireframe does not come in contact with your ears. Now quickly spin around.
From The Physics Classroom Online high school physics tutorials
Fill a medium sized beaker, wide-mouth glass, or coffee cup 1/2 full with water. Place the container, a pizza pan, a cardboard cylinder fashioned from a file card, and a hard-boiled egg near the edge of a table as is shown in the figure. The egg and cylinder must be directly over the beaker. Also, the pizza pan must extend beyond the edge of the table. Believe it or not, the object of this activity is to knock the pizza pan and cardboard cylinder out from under the egg so that the egg will fall straight down into the beaker!
To accomplish this feat, a broom will be used as a pizza pan “launcher.” Place the broom handle next to the edge of the pizza pan. With your foot on the bristles of the broom, “cock” the broom by pulling the handle away from the pan. This will put the handle under tension. Now, without hesitation, release the handle. With luck, the egg should drop into the beaker. For a greater challenge, increase the number of eggs, beakers, etc.
In this “eggsperiment” you will use two eggs, one marked with an “O”, the other with an “X.” Spin the egg marked with an “X.” Now stop the egg with your hand. Immediately after the egg stops, remove your hand. Describe what happens. Now spin the egg marked with an “O.” Again stop the egg with your hand and then quickly release it. Describes what happens this time.
(Teacher’s note: One egg is raw and the other is hardboiled)
Give the “Strobe Revolution” a gentle spin and watch it continue spinning in a state of near perpetual motion. Amazing!
Newton’s 2nd Law: Jelly Jar Accelerometer
An accelerometer is a device that may be used to determine the direction of an object’s acceleration. An accelerometer also gives the direction of any unbalanced force acting on an object. There are many types of accelerometers. One of the simplest is made out of a jar, a bobber and some string.
To construct an accelerometer, glue a string to the inside center of the lid of a jelly or peanut butter jar. The length of the string should be slightly less than the height of the jar. For reasons of safety, a plastic jar is always preferable. Attach a plastic bobber to the free end of string. After filling the jar with water, with the bobber and string on the surface of the water, place the lid on the jar. Now tighten the lid and invert the jar. The bobber should now be located just below the glass bottom of the jar. If it’s dragging on the glass bottom, remove the lid and slide the bobber along the string so that it is closer to the lid. You are now ready to use your accelerometer.
Newton’s 3rd Law: That’s Repulsive!
Obtain two small magnets. Can you make the two magnets attract each other? Repel each other? Place the two magnets on the table and align them so that they repel each other. Bring them close together and then release them.
Arrange two small magnets so that they attract each other. Separate the
magnets so they are one or two centimeters apart and then release them.
Using two spring scales, have a tame “tug of war” with your partner. Observe the readings on the two scales during the tug of war (don’t pull too hard!).Questions:
The Big Push…
With your lab partner, hold two bathroom scales back to back. Now push on the scales and observe both readings.
Up Up & Away!
The Balloon Helicopter is a toy Newton would have loved! Blow up the balloon and attach the hub to the blade assembly. Now release the helicopter and watch it go!
The students have completed the exploratory. What’s next? During the next segment of the learning cycle, the concept development phase, basic principles emerge, terminology is introduced, and mathematical relationships are derived. With the teacher serving as a guide, students construct meaning from observations made during the exploratory. How is this accomplished?
I generally engage students in class discussion immediately after their laboratory activity. The wonderful news is that students do not have to be coaxed into participating. The exploratory almost always leaves kids with unanswered questions. This produces what Piaget referred to as disequilibrium. In this state, students have a need to know and are motivated to ask questions. This phase is particularly exciting because the teacher and students are given an opportunity to listen to each other’s explanations. With the guidance of the teacher, meaning and understanding begin to emerge from conflicting ideas.
In addition to discussion, a variety of methodologies may be employed during this concept development stage of the learning cycle. They include reading, computer work, or demonstrations. At this time, it may even be appropriate for the students to return to the laboratory to test a hypothesis that was brought up during class discussion.
During the last phase of the learning cycle, students return to the laboratory where they engage in real-life applications of their newly acquired knowledge. These activities may be done in a conventional laboratory or in some rather unorthodox settings. Regardless of the venue, students apply the physics they have just learned in a meaningful and quantitative way.
For the last 25 years we’ve had students push cars with bathroom scales in the school’s parking lot as an application of Newton’s Second Law of Motion. The bathroom scales provide a known force and regularly dropped safety cones are used to obtain the vehicle’s acceleration. We use the acceleration and force to calculate the vehicle’s mass. While this may seem a little strange, it illustrates to students that the material studied in class pertains to objects both small and large. Of course students always want to push things to the limit and this annual event is certainly no exception.
Each year I ask students to bring in their own cars for the lab. I usually get cars ranging from a sub compact to a SUV. A few years ago a student said he could arrange for a couple of vehicles that might be interesting to use, but he wasn’t saying what he had in mind. When my class convened in the parking lot the next day, there sat a school bus and a Hummer ready to be pushed. Mind you, this was when the Hummer had just become commercially available. Not only did my students go wild, but there were cheering students, teachers and administrators leaning out of every single window of our four-story school.
As my students pushed the two “monsters of the midway” and a variety of other cars and trucks, hundreds of witnesses saw Newton come through one more time. It might be said that conventional learning went out the window for a while that day, but the force was certainly with real-life physics!