Hands-on Activity Swinging with Style

Learning Objectives

After this activity, students should be able to:

• Explain why a swing can be described as a pendulum.
• Explain the effects of gravity and inertia in a pendulum.
• Use the engineering design process to develop a new invention using what they have learned about pendulums.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• Access to one playground swing
• Stop watch
• Pencil
• Chair (optional; can also be shared by teams)
• Swinging with Style Worksheet

Worksheets and Attachments

Pre-Req Knowledge

Exposure to the concepts of gravity, pendulums and inertia as discussed in the associated lesson, The Science of Swinging.

Introduction/Motivation

What is a pendulum? (Listen to student descriptions and clarify if necessary.) A pendulum is a mass (or weight) hanging from a string or rod that swings freely Can anyone think of a pendulum that you have seen on a playground? What about a swing on a swing set? When you are on a swing, you are the mass that is hanging by the swing chains. When you swing back and forth, you become a pendulum!

Remember Newton's first law of motion? (Listen to student definitions and clarify if necessary.) An object at rest stays at rest and an object in motion stays in motion, unless there is an outside force to change that. So, when you first sit down on a swing, you are an object at rest. And, you stay at rest until you push off the ground and pump your legs. Once you get going, you do not really have to do much work because an object in motion stays in motion (due to inertia). What keeps you from flying all the way up and around the top of the swing set? (Listen to student explanations.) It is gravity that brings you back down to the ground when you get too high. What do you think pulls you back in the other direction (either forwards or backwards)? It is inertia that keeps you moving back and forth.

Today, we are going to use the swings to experiment with pendulums. We are going to take some measurements to see how a pendulum moves. First, let's define some pendulum terms. (It may be helpful to draw a simple sketch on the classroom board as you define these terms.) A period is the time it takes the pendulum bob (you) to swing back and forth once. So, let's say you start a timer when you are swinging at the top front, then you swing down towards the back, and then down again towards the top. When you get back up to the top front, if your timer says 3 seconds, then the period of the pendulum is 3 seconds. The rate of a pendulum is the number of swings that are measured in a certain amount of time (such as one minute). So, if you swung back and forth 20 times in one minute, then the rate of the pendulum is 20 swings per minute. Today we will measure our pendulum rate on the swing, and figure out how we can change the rate of a pendulum.

Many other objects move back and forth regularly like pendulums, such as a weight bouncing up and down on a spring, and the back and forth movement of radio waves. Engineers use their knowledge of pendulums when designing many things. For example, engineers carefully consider how much swaying back and forth a building can safely withstand during a windstorm. Engineers also use pendulums to measure earthquakes (seismometers) and determine how much local gravity is at any point on the Earth (gravimetry). Engineers even use pendulums to navigate spacecraft and aircraft.

The most familiar use of a pendulum is a clock. Have you ever seen a grandfather clock with a pendulum swinging back and forth under it? Well, today we are going to look at the motion of a pendulum and use that to design a human-powered clock. We'll learn about the seven steps of the engineering design process. For what purposes do you think a human-powered clock might be useful? Well, think about that as we learn more about pendulums.

Procedure

Background

Newton's first law of motion describes the concept of inertia: an object at rest stays at rest and an object in motion stays in motion, unless acted upon by an outside force. The upward movement of a swinging pendulum is due to inertia; its downward movement is due to gravity. Together, gravity and inertia cause the pendulum to move the way it does — a continuously swinging motion.

As engineers work together to design new products, they follow the steps of the engineering design process: 1) ask: identify the need and constraints; 2) research the problem; 3) imagine: develop possible solutions; 4) plan: select a promising solution; 5) create: build a prototype; 6) test and evaluate prototype; 7) improve: redesign as needed. Throughout the process, emphasis is placed on cooperative, creative teamwork, in order to achieve the best possible results.

Before the Activity

• Gather materials and make copies of the Swinging with Style Worksheet.
• Divide the class into teams, one team for each available playground swing.

With the Students

1. Have one student from each team sit on a swing and have students make observations about the forces acting on the student when he/she first sits on the swing. Then have the student start swinging and also note observations about the effects of forces when the student pushes off and pumps his/her legs. This person is designated as the team's swinger. Direct the swingers to pump until they are fairly high, but not to the point that the swing jumps or bounces around. This forms the target swing cycle, to create a regular pendulum swing.
2. Ask students to take note of the highest point of the swinger during the target swing cycle, because this is the point from which they will start all timing measurements. (Tip: It sometimes helps to note the location of the swinger's shadow compared to the shadow of the swing set.)

3. Have another student in each group volunteer to be the team's timekeeper. Have this student start the stopwatch when his/her team's swinger is at the top front of his/her swing cycle, and stop the stopwatch at 60 seconds, for each of the timing trials.
4. All the remaining team members are the counters. They count the number of times the swinger returns to the front top position during 60-second timing trials. A full swing is the movement of the swinger back and forth. Note: To collect good data, it is important for the swinger to keep a constant speed. (See the Troubleshooting Tips section for more on how to keep a constant speed.)
5. After each 60-second timing trial, one counter from each team records on the team worksheet the number of swings the swinger completed. Have the swinger repeat this procedure for at least three trials or modify the activity with any of the following options:

• (Optional) To rotate roles and gather more data, repeat steps 1-5 so that each team member gets a turn being a swinger.
• (Optional) To gather data with a heavier swinger (bob), repeat steps 1-5 with the teacher or another adult as the swinger. If only one adult is available, have all the groups take data from this trial. Remind the adult to achieve the same target swing height as the previous trials before starting the 60-second timing.
• (Optional) To gather data for a shorter pendulum, shorten the length of the chains. With the students at a safe distance, have an adult toss a swing over the swing's horizontal support bar two or three times. Standing on a chair makes this task easier, but be careful. Have the teacher help a swinger get on the swing. Repeat steps 1-5, remembering to achieve the same target swing height as the previous trials before starting the timing.

6. Have student teams complete the worksheet chart, graph and questions.
7. Have the students figure out the number of swings for their pendulum in one hour. For example, if the swinger had 10 swings in one minute, how many might they have in an hour if they stayed at the same speed? (Answer: Assuming no friction, 600 swings per hour.)
8. Next, tell the students that they are teams of engineers who are going to use what they have just learned about pendulums to create a new invention. Have them brainstorm ideas for how they could use the rate of the pendulum to make a Human-Powered Swing Clock. Explain the steps of the engineering design process.
9. Have students draw their design for a Human-Powered Swing Clock on their worksheets.
10. Ask students to think about purposes for which their Human-Powered Swing Clock might be useful. (Possible applications: Perhaps to measure the duration of recess or lunch, or maybe to time students running races across the playground.)
11. Have students share their invention ideas and explanations with the rest of the class.

Vocabulary/Definitions

bob: The weight at the end of the string or rod of a pendulum.

brainstorming: A method of shared problem solving in which all members of a group quickly and spontaneously contribute many ideas.

engineer: A person who applies his/her understanding of science and math to creating things for the benefit of humanity and our world.

engineering design process: A multi-step, cyclical process used by engineers to create a product or system. Combines an understanding of science and math to use available resources to meet a desired goal.

friction: A resistance to motion.

gravity: The Earth's force that pulls everything downward.

inertia: The property of an object to stay moving unless it is stopped by an outside force.

Newton's first law of motion: An object in motion stays in motion and an object at rest stays at rest, unless acted upon by an outside force.

pendulum: An object attached to a fixed point by a string or rod so that it can swing freely under the influence of gravity and acquired momentum. Often used to regulate devices, such as clocks.

period: The time for one pendulum swing (back and forth). A period is determined by only two factors: length and gravity.

Assessment

Pre-Activity Assessment

Prediction: Ask students to make predictions for the activity. What factors might change a pendulum's rate? Would changing the mass of the bob change the rate? Would changing the length of the pendulum change the rate? (Encourage all predictions and explanations at this stage; they will learn the answers during the activity.)

Activity Embedded Assessment

Group Questions: During the activity, ask the teams:

• What makes a swing similar to a pendulum? (Answer: A swing is a bob [weight] attached to a fixed point [top of the swing set] by chains that can swing freely.)
• Why do you need to push and pump to get yourself going in the first place? (Answer: Newton's first law of motion describes this behavior in our natural world: objects at rest stay at rest unless there is something to push them.)
• What makes you (or any pendulum bob) keep coming down to the ground and not flying off into the air? (Answer: The Earth's gravity.)
• What makes you (or any pendulum bob) keep going up? (Answer: Inertia, or Newton's first law that states that objects in motion stay in motion unless acted upon by an outside force.)
• Can you feel the inertia pulling your body up, and the gravity pulling your body down?
• How could we change the rate of the pendulum swing? (Answer: Changing the length of a pendulum changes the time it takes to complete a swing; the shorter the pendulum, the faster it swings. Changing the weight at the end of a pendulum does not change the rate at which the pendulum swings. A period is determined by only two factors: length and gravity.)

Post-Activity Assessment

Data Analysis: Have students look for patterns in their data and use that data to predict future motion. 

Show and Tell: Have students show their engineering design to the rest of the class, and describe what is unique about their design. Ask them to explain the engineering design process steps they used to create their invention. Ask them to explain for what helpful purpose their swing clock could be used.

Sales Pitch! Have students pretend to be salespeople promoting the benefits of their Human-Powered Swing Clock to a manufacturer or consumer. Have teams create a persuasive poster or flyer, as well as a 10-minute sales pitch of their design for presentation at the next class. Include in their sales pitch the parts and features of the clock, as well as its purpose.

Safety Issues

• Warn students not to jump off the swings.
• Warn walking students to watch out for students on the swings.
• When throwing the swing over the top horizontal swing set pole to shorten the chain, make sure no one is close enough to get hit by the swing. And, take extra care when swinging with the shortened chain. Remember to unwrap the chain before leaving the playground.

Troubleshooting Tips

Try to keep the starting height consistent so that data within and among teams is comparable.

While students are swinging, they should not be pumping hard, if at all. They should try to swing at a consistent speed during the timing.

In ideal conditions, students would not need to pump at all to maintain consistent swinging motion, and this may work if students keep their legs straight out in front of them. However, the shape of a human body creates a lot of friction in the air (which acts as an outside force). Additional friction comes from where the chain connects to the swing set support bar. Explain these friction conditions to more advanced students. Advise students to counteract the friction forces by pumping just the minimal amount needed to achieve a constant speed during the timing.

Activity Extensions

Make a Seismograph: Have students create their own seismometers as described in the fourth-grade TeachEngineering Seismology in the Classroom activity in the Natural Disasters unit. Students use common classroom materials to make and explore seismometers and how they relate to pendulums.

Pendulum Bowling: Have students create a pendulum from string and a weight that could be used to knock something over, such as empty plastic beverage bottles or domino tiles. Have students test their designs and determine the best place to position their pendulum for the most accurate collision with the objects.

Pendulum Clock Design: Ask students to calculate a chain length that makes the pendulum swing exactly 60 times per minute. How would this be useful? (Answer: If each swing took one second, a pendulum swing could be used as a regular clock.)

Activity Scaling

• For lower grades, work through the activity and worksheet as a class, going through each step together as the experiment progresses. Simplify the activity by not conducting all of the options described in the Procedure section.
• For upper grades, further students' understanding of Newton's first law of motion by explaining the friction conditions described in the Troubleshooting Tips section. Also, ask students to measure the period of the pendulum in addition to the rate. Have them think about how friction might change their Human-Powered Swing Clock. What could they do to reduce the effects of friction, to make their human-powered clock more consistent in timekeeping?

Additional Multimedia Support

Amusement Park Physics – Pendulum. Annenberg Media. Accessed July 17, 2007. http://www.learner.org/exhibits/parkphysics/pendulum.html

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.