Science/8/Focus on Physical Science 1.0 The velocity of an object is the rate of change of its position. As a basis for understanding this concept:
a. Students know position is defined in relation to some choice of a standard reference point and a set of reference directions.
b. Students know that average speed is the total distance traveled divided by the total time elapsed and that the speed of an object along the path traveled can vary.
c. Students know how to solve problems involving distance, time, and average speed.
d. Students know the velocity of an object must be described by specifying both the direction and the speed of the object.
e. Students know changes in velocity may be due to changes in speed, direction, or both.
f. Students know how to interpret graphs of position versus time and graphs of speed versus time for motion in a single direction. 2.0 Unbalanced forces cause changes in velocity. As a basis for understanding this concept:
a. Students know a force has both direction and magnitude.
b. Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.
c. Students know when the forces on an object are balanced, the motion of the object does not change.
d. Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.
e. Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).
f. Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.
g. Students know the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system.
Students will create an apparatus which will enable them to whirl a stopper on a string and while simultaneously reducing the radius of the circular motion. Using this apparatus, students will investigate concepts of conservation of angular momentum and centripetal force. Students will then describe and explain other situations, both in sports and elsewhere, where the conservation of angular momentum can be observed.
Students will conduct a qualitative investigation of the relationship between the radius and the rotational speed of a stopper that is tied to a string and whirling in a circle. The students will make a hypothesis, conclusion, and present their findings to their peers. Through discussion, they will formalize an understanding of the conservation of angular momentum. They will apply the concepts they develop in this activity to other situations they have witnessed.
Students will be able to:
Formulate a hypothesis.
Describe their investigation using words and pictures.
Record observations about the relationship between rotational speed and radius.
Interpret their observations to form a conclusion.
1 rubber stopper with hole (other soft/blunt object can be used if it there is a way to securely fasten them to a string), 4 feet of string or fishing line, the barrel/tube from a ball point pen, safety glasses for each student
Optional: Rotating office chair
Anticipatory Set (Lead-in):
Ask if any students have ever watched Olympic figure skating or Olympic diving. Ask if anyone can guess how these sports are similar to water swirling down into a bathtub drain. Discuss with them briefly that circular or rotational motion is involved in all these cases. Tell them that they are going to watch a short video on the science of figure skating and then do a short activity to learn some details about circular motion and angular momentum.
Lesson Plan Procedure:
Note: This lesson assumes prior knowledge of inertia and the conservation of momentum. If necessary, these should be briefly reviewed before the video.
Before showing the video, mention that in addition to learning about the science of figure skating, the students also will see in this video that it is possible to be an athlete and a scholar (the skater, Rachel Flatt, is also an AP Physics Student.)
Hand out the activity “worksheet: Whirling Stopper”. Go over the task and the equipment. Clarify the terms radius of curvature and rotational speed.
Give students approximately 15 minutes to complete the activity and the worksheet questions 1-4. They can also do question 5 in class or for homework.
Ask students to share their answer to question 4, the relationship between radius of curvature and rotational speed.
Closure (Reflect Anticipatory Set):
If time and equipment permit, you can use a swiveling office chair to perform the same demonstration of angular momentum that was shown in the video. Also, you can ask a student to describe more specifically how this relates to diving, and specifically why do divers tuck?
Another closure option is to watch a slow motion video of a figure skating “quad” jump which involves four turns in one jump. The students can watch and clearly see the arms and legs go in to increase rotational speed and then go out to slow down the rotational speed upon landing.
Assessments & notes
Plan for Independent Practice:
Have student think of an example not discussed in class and answer question 5.