5.2 Angular Motion. Motion and Force. Objective. Materials. Introduction /// TEACHER ALERT /// Directed Instruction. Content

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1 5.2 Angular Motion Motion and Force Objective Students will define angular motion and distinguish between rotational and periodic motion. Materials Blackline Master 5.2A Discover: Amusement Parks Blackline Masters 5.2B C Levers Blackline Masters 5.2D E Yo-yos (ADDITIONAL ACTIVITY) Transparency T-05A Wild Rides /// TEACHER ALERT /// For Lesson 5.6, you will need to collect broken compound machines. A note can be sent home to parents asking for old or broken items including radios, fishing poles, action figures, toy cars, typewriters, rotary telephones, egg beaters, etc. Make sure to notify parents and students that the items brought in will be disassembled by students and will no longer be operative. Content Lesson 5.1 concerned linear motion. In this lesson, students study the other common type of motion angular motion which involves motion about a fixed point in space. It is called angular motion because an angle is formed between one position of the object, the center of the circle, and any second position of the object after it has moved. There are two types of angular motion. The first is motion in a complete circle; this is called rotational motion. This type of motion occurs around a central point, which is the center of the circle. When an object in rotational motion returns to its original position, it has completed a revolution. There are many examples of rotational motion for example, the hands of a clock, planets in the solar system, tires on a car, blades on a helicopter, the reel of a fishing rod, and the wheel of a ship. Periodic motion, which is back and forth motion as occurs in the motion of a pendulum, is similar to rotational motion, but only a portion of a circle is completed. In periodic motion, though an object doesn t swing completely around, it still moves around a central point. If a pendulum had enough energy to make a full rotation, it would show rotational motion, not periodic motion. Without sufficient energy, gravity pulls the pendulum back down. As the pendulum swings downward, it gains enough speed to swing up to the other side. However, it still lacks the energy to fully rotate; therefore, the pendulum swings downward and this process is repeated. Introduction Distribute Blackline Master 5.2A Discover: Amusement Parks to each student. Read the introductory paragraph with the students. Explain to students that they will be identifying different kinds of motion in amusement park rides. Review the words in the Word Bank to make sure that the students understand the different kinds of motion. Not all the words will be used; some may be used more than once. Show students Transparency T-05A Wild Rides and instruct them to write words from the Word Bank on the blanks for each picture. Guide students through the Conclusion questions. Have students complete the I wonder section. Directed Instruction 1 Direct students to page 87 and have them read the first sentence. Angular motion is the motion of an object around a central point. Call students attention to the picture that shows how an angle is formed as an object moves around a central point. Reproduce the drawing on the chalkboard and demonstrate rotational motion. Demonstrate to students how your arm moves around a central point your shoulder joint. Continue reading the text. One type of angular motion is rotational motion. Rotational motion is the motion of an object in a complete circle. Ask students What are some other objects that rotate around a central point? (possible answers: planets, bicycle wheels, spinning top, tornadoes, hurricanes) 2 Direct students to page 88 and read the top of the page together. Periodic motion is the back-and-forth motion of an object from a central point. Have students examine the drawing of a swing. Explain to students that a swing goes back and forth around a central point, but its motion is only a portion of a larger circle. Ask students What are some other objects that show periodic motion? (possible answers: swinging door, pendulum, 110 Purposeful Design Science, Level Three All rights reserved.

2 windshield wiper) The amount of time it takes for a pendulum to return to its original position is called a period. 3 Have students complete the activity at the bottom of page 88. When they are done, ask volunteers to share their answers. Ask each volunteer to identify the central point around which the object moves. 4 Distribute Blackline Masters 5.2B C Levers to students. Explain that the lever is an example of angular motion. A lever is a rigid bar that rotates about a pivot point known as a fulcrum. Levers are found in many tools. Have students complete the blacklines. Ask for volunteers to share their answers. You may have to guide some students in identifying the pivot point on the tools. 5 Ask students, How does angular motion help us? How would our lives be different without it? (Answers will vary.) These questions will help the students to process the information they have acquired and to integrate that information with other knowledge they already have. Additional Activities Students can look in magazines and newspapers to find photos of objects that show angular motion. Have them cut out the photos and create a poster collage. Make sure their photos show both rotational and periodic motion. Divide students into pairs. Distribute Blackline Masters 5.2D E Yo-yos to each student and a yo-yo and stopwatch to each pair. Read the first paragraph. Demonstrate to students the motion of the yo-yo in a loop. Students will spin the yo-yo 10 times to make it easier to time with the stopwatch. Make sure that students understand they will be counting each rotation to 10 and dividing the amount of time by 10 to get the time for one revolution. Instruct students to read the first paragraph of BLM 5.2E. Tell them that it is important to have the yo-yo at a 45 degree angle when they release it. They can use the picture to determine the angle. Students will allow the yo-yo to swing back and forth 5 times to make it easier to calculate the period of one swing. They will do this by dividing the time by 5 to get one period. 5.2 Angular Motion What is angular motion? Angular motion is the motion of an object around a central point. If you draw a line from the object to the center, move the object, and then draw another line, the two lines form an angle. When you ride on a carousel, you move around in a circle and always at the same distance from the center. This motion is called rotational motion. Rotational motion is the motion of an object in a complete circle. When an object returns to the place where it started, it has completed one rotation. Another type of angular motion is periodic motion. Periodic motion is the back-and-forth motion of an object from a central point. The amount of time it takes for an object to return to where it started is called a period. The amusement park ride acts as a pendulum. Photo courtesy of Six Flags Elitch Gardens Rotational or periodic? Identify the type of angular motion you see in each photo. Write rotational or periodic in the blank next to each photo. Rotational Periodic Top view Periodic Purposeful Design Publications Purposeful Design Science, Level Three Motion and Force Purposeful Design Publications 111

3 What is angular motion? Angular motion is the motion of an object around a central point. If you draw a line from the object to the center, move the object, and then draw another line, the two lines form an angle. When you ride on a carousel, you move around in a circle and always at the same distance from the center. This motion is called rotational motion. Rotational motion is the motion of an object in a complete circle. When an object returns to the place where it started, it has completed one rotation. 5.2 Angular Motion Top view Purposeful Design Publications 87

4 Another type of angular motion is periodic motion. Periodic motion is the back-and-forth motion of an object from a central point. The amount of time it takes for an object to return to where it started is called a period. The amusement park ride acts as a pendulum. Photo courtesy of Six Flags Elitch Gardens Rotational or periodic? Identify the type of angular motion you see in each photo. Write rotational or periodic in the blank next to each photo. 88 Purposeful Design Science, Level Three Motion and Force

5 BLM 5.2A Discover: Amusement Parks Name What is the motion of amusement park rides? Amusement park rides are lots of fun! You can move really fast, spin around quickly, or swing back and forth. Can you identify the different kinds of motion for each ride? Examine each picture of an amusement park ride that your teacher shows you. Use the Word Bank to identify the type of motion. Some pictures have more than one type of motion. Word Bank Picture 1: horizontal Picture 2: circular Picture 3: vertical swinging Picture 4: spiraling 1. How is motion used to make the ride fun? 2. What is the most common way rides move? 3. What is your favorite type of motion on rides?

6 BLM 5.2A Discover: Amusement Parks What is the motion of amusement park rides? Amusement park rides are lots of fun! You can move really fast, spin around quickly, or swing back and forth. Can you identify the different kinds of motion for each ride? Examine each picture of an amusement park ride that your teacher shows you. Use the Word Bank to identify the type of motion. Some pictures have more than one type of motion. Word Bank Picture 1: circular horizontal Picture 2: swinging circular Picture 3: circular vertical swinging Picture 4: vertical, spiraling spiraling 1. How is motion used to make the ride fun? many different ways at different speeds. 2. What is the most common way rides move? You move in circular 3. What is your favorite type of motion on rides? Answers will vary.

7 BLM 5.2B Levers Name Levers A lever is a rigid bar that rotates about a pivot point. The angular motion of a lever can be used to lift objects. To lift the object, we push down on the long end. The amount of effort it takes to lift the object depends upon the distance our hands are from the pivot point. It also depends on how far the object is from the pivot point on the other side. The general rule is that the closer the object is to the pivot point and the farther out we push on the lever, the easier it will be to lift the object. 1. Make a lever out of a ruler and a pencil as a pivot point at the position shown in the diagram. What kind of objects can you lift with this lever? Try pushing closer to the pivot point. Is it easier or harder? 2. Try placing the pivot point in the middle. Is it easier or harder to lift objects this way? Can you think of an object on a playground that this looks like?

8 BLM 5.2B Levers Levers A lever is a rigid bar that rotates about a pivot point. The angular motion of a lever can be used to lift objects. To lift the object, we push down on the long end. The amount of effort it takes to lift the object depends upon the distance our hands are from the pivot point. It also depends on how far the object is from the pivot point on the other side. The general rule is that the closer the object is to the pivot point and the farther out we push on the lever, the easier it will be to lift the object. 1. Make a lever out of a ruler and a pencil as a pivot point at the position shown in the diagram. What kind of objects can you lift with this lever? Answers will vary. Try pushing closer to the pivot point. Is it easier or harder? harder 2. Try placing the pivot point in the middle. Is it easier or harder to lift objects this way? harder Can you think of an object on a playground that this looks like? see-saw

9 BLM 5.2C Levers Name Identifying Levers Each of these tools uses a lever. Circle the pivot point on each tool.

10 BLM 5.2C Levers Identifying Levers Each of these tools uses a lever. Circle the pivot point on each tool. (Either answer is correct.) Purposeful Design Publications. All Rights Reserved Motion and Force

11 BLM 5.2D Yo-yos Name Materials needed: yo-yo, stopwatch Rotational Motion Spin the yo-yo around in a loop. This is the rotational motion of the yo-yo. Let s calculate how fast you can spin a yo-yo around. Spin the yo-yo in a circle as close to a constant speed as possible. Have someone measure the time it takes for you to spin the yo-yo 10 times. Count out the number of rotations every time the yo-yo is closest to the floor. Stop at 10. Time for 10 revolutions = To find the time for one revolution, divide the number above by 10. Time for 1 revolution =

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13 BLM 5.2E Yo-yos Name Periodic Motion While holding the end of the yo-yo string steady with one hand, hold the yo-yo at a 45 degree angle with the other hand. Try to match the angle in the picture. Have someone measure the time it takes for the yo-yo to move back and forth 5 times. + = 1 Time for 5 periods = To find the time for one period, divide the number above by 5. Time for 1 period =