# Newton's 3rd Law: Newton's Cradle & Expo (9 of 9)

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## Objective

Students will be able to use a Newton's Cradle to experiment with Newton's 3rd Law.

#### Big Idea

Newton's 3rd Law can be demonstrated most effectively with a Newton's Cradle.

## NGSS Background

This lesson is based on California's Middle School Integrated Model of NGSS.

MS-PS2 Motion and Stability: Forces and Interactions

PE: MS-PS2-1 - Apply Newton's Third Law to design a solution to a problem involving the motion of two colliding objects.

DCI: PS2.A - For any pair of interacting objects, the force exerted by the first object on the second object is equal in strength to the force that the second object exerts on the first, but in opposite directions (Newton's 2nd Law).

Science and Engineering Practices 7: Engaging in Arguments from Evidence

Crosscutting Concept: Cause and Effect

This activity can be used as a stand alone lesson or can be placed with eight other lessons, designed as an exposition to be experienced over three days.

Newton's Laws Expo contains:

I have also developed three demonstrations of Newton's Laws

Demonstrations

In this lesson, students engage in a short (eight minute) activity designed to demonstrate one of Newton's Laws. Suspended bowling balls interact, showing that an action has an equal reaction (MS-PS2-1). When more bowling balls are added to the action an equally greater number of bowling balls will react (PS2.A). It will be the student's responsibility to use evidence recorded during the activity to determine that Newton's 3rd Law is being expressed, showing that any action has an equal and opposite reaction (SP7). Each activity has been carefully chosen to replicate a specific effect (CCC).

## Set-up

360 minutes

Needed Materials

NOTE: Newton did not create this contraption. It was sold in the 1960s as a desk toy and named in honor of Newton.

Directions for building a bowling ball sized Newton's Cradle in your classroom

The first order of business is to select a suitable location for your Newton's Cradle. I found a spot that was open (allowing a full range of motion) and had a strong beam above the drop down ceiling in order to anchor the rig. I used 1/4 inch steel cable cut to 4 feet lengths. I carefully installed eye bolts into five bowling balls and used locking clips. The bowling balls were purchased from a local thrift store.

I had the high school metal shop build a 1/2 inch stock metal frame with beam clamps as attachment points. The size of the frame was dictated by the spacing of the ceiling panels. Chain links were welded 8 inches apart on either side of the frame to provide the correct spacing.

Here is a close up photo of the beam clamp. I took several photos of the location and explained what I wanted to the high school metal shop teacher and he was excited to build something, especially when I told him it had to remain hidden most of the year.

If building a bowling ball sized Newton's Cradle is too much, a smaller desktop version can be purchased instead. The desktop version will demonstrate the same laws of motion as the bowling ball version will.

Mythbusters built a larger version using wrecking balls.

Print out a copy of Station Markers. Tape 'Station 9' marker card down to the desk where you intend students will conduct this activity. Each station marker identifies where the activity will take place and provides directions for completing the activity.

Print out a copy of Newton's Laws Exposition packet for each student. The packet includes directions and questions to answer. If you are performing this lesson as a single activity you will only need to print out Activity 9.

This activity is designed to accompany other Newton's Laws Activities. I run this unit as a three day exposition. Day 1 is reserved for showing all the students the nine activities. Days 2 and 3 allow for an eight minute rotation. I typically have my students experience five activities (40 minutes) on Day 2 and four activities (32 minutes) on Day 3 followed by a recap of the events.

## Student Activity

8 minutes

Newton's Third law will be in effect for this lesson. Newton's Third Law states that for every action there is an equal and opposite reaction.

Students will not know what specific law of motion they will be experimenting with. They have to record what they see, gather evidence, and argue about what law is being manipulated.

SAFTY TIP: I make sure my students know that any object placed in between the bowling balls will be destroyed (pencil, water bottle, hand, etc). They are told that if a finger gets caught between the bowling balls the forces generated will pound a finger into hamburger meat. They may NOT place anything in between the bowling balls at any time. I provide constant adult supervision at this station and will remove this rig for everyone if ONE person breaks the rules.

Safety Rules

1. No items may be placed between the bowling balls.
2. No force may be added to the falling bowling balls.

Directions

1. Pull one bowling ball up and release it. Record your observation.
2. Pull two bowling balls up and release it. Record your observation.
3. Pull three bowling balls up and release it. Record your observations.

Student Work Sample

## Extensions

45 minutes

Newton's Law are expressed in a multitude of ways in the English language because Newton's original text ' Philosophiæ Naturalis Principia Mathematica', often referred to as the 'Principia', was written in Latin (as were all scientific articles in that time) and translated into English. As such, there are many different translations, causing confusion with students.

I teach Newton's Three Laws with this translations.

1. An object in motion will reamin in motion and an object at rest will remain at rest - unless acted upon by another force.
2. Acceleration is based on force and mass (F=ma).
3. For every action there is an equal and opposite reaction.

To assit in teaching Newton's Law before this lesson is taught, I have included three Powerpoint lessons: