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TE Activity: You're a Pushover!

The purpose of this activity is to demonstrate Newton's 3rd Law of Motion, which is the physical law that governs thrust in aircraft. The students will do several activities that show that for every action there is an equal and opposite reaction.

Engineers apply their understanding of scientific principles, such as Newton's laws of motion, and mathematics to design, analyze and improve their inventions. Engineers use algebra and basic math skills to determine exact values for variables such as velocity, temperature, acceleration, energy and mass. Using these real measurements and calculations enables engineers to design efficient, safe and successful aircraft.

Learning Objectives
Materials
Introduction/Motivation
Procedure
Attachments
Safety Issues
Troubleshooting Tips
Assessment
Extensions
Activity Scaling

Grade Level: 5 (4-6)	Group Size: Not defined
Time Required: 20 minutes	Activity Dependency : None
Expendable Cost Per Group : US$ .50
Keywords: airplanes, Newton, laws of motion, thrust, flight, acceleration, mass

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Colorado Math
- 1. represent, describe, and analyze patterns and relationships using tables, graphs, verbal rules, and standard algebraic notation; (Grades 5 - 8) [2005]
Colorado Science
- Standard 1: Students understand the processes of scientific investigation and design, conduct, communicate about, and evaluate such investigations. (Grades 0 - 12) [1995]
- Standard 5: Students know and understand interrelationships among science, technology, and human activity and how they can affect the world. (Grades 0 - 12) [1995]
- 2.1 Students know that matter has characteristic properties, which are related to its composition and structure. (Grades 0 - 12) [1995]
- 2.3 Students understand that interactions can produce changes in a system, although the total quantities of matter and energy remain unchanged. (Grades 0 - 12) [1995]

Thrust is based on Newton's 3rd Law of Motion. It states that for every action there is an equal and opposite reaction. This means that when you push something, it actually pushes you back. That is the reason you brace yourself to push something heavy, such as a huge snowball for making a snowman. You could not just stand straight up and push against a wall. You would fall over backwards! It would be just the same as if someone standing in front of you had pushed you over.

An airplane needs something to push it forwards so it uses the air around it. The air will not push the airplane forwards on its own, and the airplane certainly cannot tell the air to push it forwards; the airplane actually pushes air backwards. It does this by increasing the pressure of the air in the combustion chamber and pushing it out the back of the engine. When the action of the airplane pushing air out of the back of the engine occurs, the opposite reaction is that the airplane moves forward.

Newton's 3rd Law can be written as: the mass of object 1 x the acceleration of object 1= the mass of object 2 x the acceleration of object 2. Or more specifically as: m₁ x a₁ = m₂ x a₂.

Before the Activity

Try the demonstrations, and review the worksheet ahead of time.
Make copies of the worksheet.

With the Students

Part 1: You're a Pushover!

Distribute the activity worksheet to students.
Take the students to an area where they can each stand in front of a section of wall. (i.e., outdoor sides of the school building, hallway, or a gym).
Tell the students to push on the wall as hard as they can. Students will instinctively brace themselves before pushing. Ask them what happened. They should notice that they did not fall over and the wall did not move.
Now tell students to stand upright and flat-footed, close to the wall. Have them push as hard as they can. What happens? (Answer: Students will be pushed backwards by the wall.)
Have students answer the Part 1 questions on their activity worksheet.

Part 2: Pushing on Air!

Hand out a balloon to each student. Guide students through the activity as follows:

Blow up the balloon just a little bit. (Note: demonstrate to students how to stretch the balloon while it's deflated to make the first blow up easier.)
Gently let the air out of the balloon without letting the balloon go. Feel the stream of air as it comes out.
Blow up the balloon until it is almost full.
Gently let the air out again and feel the stream of air. You should feel the air come out much faster because the pressure inside the balloon is greater.
Blow up the balloon a little bit and let it go. Do the same with the balloon filled all the way. Notice how much faster the balloon accelerates when it is full.
This demonstrates Newton's 3rd law: every action has and equal and opposite reaction. The force of the air leaving the balloon is equaled by the force of the balloon moving forward. A small balloon travels more slowly and a shorter distance than a big balloon because a big balloon releases more air!

Part 3: Gotta be Equal

Remind students that Newton's 3rd Law of Motion states that for every action there is an equal and opposite reaction.
Students will be calculating the missing mass or acceleration based on the equation for Newton's 3rd law.
Have students complete the activity worksheet.

You're a Pushover! Activity Worksheet

Ensure that students act responsibly with the balloons. You may want to conduct this activity outside or in a gym to allow students sufficient space to let their balloons fly.

Students should have a firm grasp of mass before this activity, but acceleration may be a new concept for them. For this activity, it will suffice to define acceleration as how fast or slow something speeds up or slows down (for example, when a car passes on the highway, or the earth's gravity).

It may be easier to explain Newton's Third Law (for every action, there is an equal and opposite reaction) in more elementary-friendly terms, such as, "When you push something, it actually pushes you back."

Pre-Activity Assessment

Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the number of true and false and write the number on the board. Give the right answer.

True or False: Thrust is based on Newton's 3rd Law of Motion. (True)
True or False: Newton's 3rd Law of Motion states that for every action there is an unequal but similar reaction. (False: the law states that for every action there is an equal and opposite reaction.)

Activity Embedded Assessment

Worksheet/Pairs Check: Have the students record observations of Parts 1 and 2 and complete the associated questions on their worksheet.

Post Activity Assessment

Problem Solving: Have students use their worksheet to work through a series of mass and acceleration problems related to the lesson.

Figure Drawing/Discussion: Have student volunteers label some of the forces of flight on objects drawn on the board.

Draw a simple balloon on the board. Ask the student volunteers to come up to the board and draw an arrow that represents thrust. What is giving the balloon thrust? (Answer: The air from inside the balloon makes it move forwards.) What arrow is going to be opposite of thrust? (Answer: drag) Let the students know that they will be learning about drag next. Next, ask a volunteer to draw an arrow that represents weight. (Answer: This arrow will be pointing down.) Next have a volunteer draw an arrow that represents lift. (Answer: This arrow will be pointing up.)
For an example that is a little more difficult: Draw a simple rocket on the board. Ask the student volunteers to come up to the board and draw an arrow that represents thrust. What is giving the rocket thrust? (Answer: the rocket fuel gives it thrust just as air from the balloon makes it move forwards.) What arrow is going to be opposite of thrust? (Answer: drag) Let the students know that they will be learning about drag next.
Next ask a volunteer to draw an arrow that represents weight. (Answer: This arrow will be in the same direction as drag, pointing down.) Next have a volunteer draw an arrow that represents lift. (Answer: This arrow will be in the same direction as thrust, pointing up.) Ask the students why the arrow goes in the same direction as thrust. (Answer: Because the rocket's forward movement is up.) Ask if any students can think of other examples of the four forces of flight and what arrows they would draw on them.

This suggestion is good if small scooters, like the square kind used in gym class, are available. Have the students sit on the scooters and push off of each other with their feet. They will see how the larger person will not go as far as the smaller person. Care should be taken in this activity because kids could fall off of the scooters and hurt themselves if they lose their balance or push off too hard.

You could also do the above extension activity using two students on roller blades/skates or on rolling desk chairs.

Another great activity to explain the concept of Newton's 3rd Law is balloon rockets (may use Activity 2 in Lesson 4 of the Mechanics Mania unit. Please see Figure 1 for illustration of concept). One idea is to set up balloon rocket stations, or strings, at different distances. Have the students try to figure out how to get their rockets to go exactly the right distance.

A line drawing of the action-reaction rocket, showing construction detail and the rocket moving along a string between two chairs.

Figure 1. Action-reaction rocket activity set up.
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Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder Tom Rutkowski, Alex Conner, Geoffrey Hill, Malinda Schaefer Zarske, Janet Yowell © 2004 by Regents of the University of Colorado.
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last Modified: April 27, 2006