Becky McCoy
Lesson Title: Introduction to Circular Motion
Timing: 60 minutes
Target Audience: 11th and 12th Grade Physics Class
Objectives: Students Will Be Able To: • Define Centripetal Force • Describe Circular Motion with words and pictures • Give examples about Circular Motion & Centripetal Force • Use thought experiments to determine what would happen in a hypothetical situation The Teacher Will Be Able To: • Identify confusion about Centripetal and Centrifugal Forces • Introduce students to Circular Motion concepts. The aim is not to give equations or specific answers this lesson, but expose students to material.
Standards Assessed: New York State Standards •
Standard 4.5.1 Explain and predict different patterns of motion of objects (e.g., linear and uniform circular motion, velocity and acceleration, momentum and inertia). o xi. Verify Newton’s Second Law of Circular Motion
Misconception(s) Addressed: • Centrifugal force • Objects moving in a circular motion will remain in that pattern even if the centripetal force is removed
Prior Knowledge: Mechanics and Kinematics Units Aim: Explore Circular Motion and Centripetal Force Concept Map Vocabulary: No concept map created for this unit.
Necessary Preparation: COPIES MATERIALS • One marble for each group • One Manila folder for each group
Becky McCoy • • • •
String with rubber washer attached at the end Large beaker Rubber ball Computer with projection equipment
SET UP • Have pieces assembled for activity • Have videos loaded before class
Becky McCoy
Lesson Plan Aim: Explore Circular Motion and Centripetal Force Physics Push-Up: Circular Motion Thought Experiments (5 minutes) Students read description of Circular Motion demonstrations and use thought experiments to discuss the viability of each with the person sitting next to them. Before cleaning the floors in his apartment, Isaac Newton decides to try a Physics experiment. He fills his bucket halfway with water. He then spins the bucket in a vertical circle at a constant speed. When the bucket is over Mr. Newton’s head, what will happen to the water? After getting dressed for an evening of astronomical observations, Johannes Kepler attempts to perform a Physics demonstration he had recently heard of. He took a small coin and a metal coat hanger and assembled them so the coin balanced on the bottom end of the hook of the coat hanger. Next, Kepler began to swing the coat hanger in a circle; will the coin stay on the coat hanger?
Activity: Circular Motion Examples and Discussion (35 minutes) Materials: • One marble for each group • One Manila folder for each group • String with rubber washer attached at the end • Large beaker • Rubber ball Procedure: •
Draw the diagram below (A should be slightly curved). o Ask students to predict which path the marble will take upon exiting the curved folder and describe why. • Have each group (or table) collect one folder and marble. They should hold the folder horizontal and form it into a gentle curve, holding it against the table. • One student should roll the marble towards the edge of the folder and observe the pattern of the marble once it exits the folders’ curve (A, B, or C?). See top view picture below.
C A
B
Becky McCoy
• Once students have been able to perform about 10 trials, ask students to describe what they saw and why the marble continues to travel in a straight line (Newton’s First Law). o Ask questions such as, “Why does it need the folder to follow and what happens when there’s no folder.” • Take a string with a weight at the end (rubber washer works well) and swing it above your head in a horizontal circle. o Ask students what keeps the washer in a circular pattern (the tension from the string). • Draw the following picture on the board:
Road
Car
• Ask students what keeps the car moving along the curved road? First focus on the car relative to the road and then the people relative to the road. o Car to Road: The friction between the tires and the road keep the car moving in a circular motion. A decrease in friction (due to rain, snow, etc.) could cause the car to veer off the road. Sand and guardrails could help to prevent serious accidents in these conditions. o People to Road: The car door keeps the people from continuing in a straight line. If the door were to open, the people would fall out since the force of the turning car would not keep them moving in the circular direction. • Complete the circular road that was started above on the board. Face in the direction of the board and point with your right hand in the direction of the car’s natural velocity and with your left hand where the force is pulling (the center). Repeat this at the top, the left, and the bottom of the “road”, showing that the force is always pulling towards the center of the circle, hence Centripetal Force. • Finally, place a ball in a large beaker. Hold the open end of the beaker and spin around. Ask students to describe why the ball does not continue in a straight line. Next, hold the bottom of the beaker and spin around, asking students why the ball flies out of the beaker. • Allow time for students to ask questions and have discussions.
Becky McCoy
Activity Summary: Video and Demonstration (10 minutes) Show the video http://www.youtube.com/watch?v=Jpbgg2TRCuw of the Hammer Throw Olympic Event. Point out the circular motion and the ball’s movement in a straight line upon release. NOTE: It would be ideal to show the Bill Nye segment on circular motion first, but it is not available online at the moment. It had Bill Nye driving in circles with a dummy in the passenger seat and when he opens the passenger side door, the dummy falls out. At this point it is important to discuss the difference between rotation and revolution. Rotation is a single object spinning around its own axis (a revolving door or the Earth). Revolution is one object moving in a circular pattern around another (the hammer around the throwers head or the Earth around the Sun). Have students stand up and rotate around their own axis by spinning to face each side of the room. Then have them revolve around their chair by walking around it twice. Select several students to explain the difference and give examples of each.
Homework: Summaries and Predictions (5 minutes) Students should write a one page summary of what they learned today including examples of circular motion in their every day lives other than what was discussed in class. Students should watch this video http://www.youtube.com/watch? v=XB8pUth5clE&feature=related and predict how the water stays in the bucket.
Exit Strategy: As students leave, have them show you the difference between revolving (around you or a friend) and rotating (spinning to face each side of the room).
Extension Activity: Show students the bucket spinning video from the homework, discuss for a bit, and hint to them that this activity will be done next class.
Assessment: Formative student assessment through question and answer Listening to student discussions Student response to homework
Resources: Mike Shum http://www.youtube.com/watch?v=XB8pUth5clE&feature=related http://www.youtube.com/watch?v=Jpbgg2TRCuw
Notes & Adaptations:
