# Newton's 1st Law Demonstration

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## Objective

Students will be able to observe Newton's 1st Law of Motion as it applies to their physical world.

#### Big Idea

Newton's 1st Law is not always intuitive to students. Providing a real world example helps them to understand the physical environment they live in.

## 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-PS2-2 - Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object.

DCI: PS2.A - The motion of an object is determined by the sum of the forces acting on it. If the total force the object is not zero, its motion will change (Newton's 1st Law). The greater the mass of the object the greater the force needed to achieve that same change in motion. For any given object, a larger force causes a larger change in motion (Newton's 2nd Law).

Science and Engineering Practices: (2) Developing and Using Models - Students will observe models (basketball on a cart, rubber band rockets on fishing line, bowling ball sized Newton's cradle) that specifically target aspects of Newton's Three Laws. These models will reduce ambiguity by demonstrating the principles of Newtonian Science without introducing misconceptions that may cause students to create an incorrect mental.

Models

1. Basketball on a cart - The basketball first represents a model of an object at rest. The cart is then propelled forward -- creating an object in motion. Once the cart is stopped, the basketball will continue to roll forward, proving that objects in motion stay in motion.
2. Rubber band rockets - Two rubber band powered rockets of different masses are flown across the classroom, proving that when force remains constant acceleration is influenced by mass.
3. Bowling ball Newton's cradle - Bowling ball sized Newton's cradle will demonstrate that when one bowling ball is pulled back its action will trigger a reaction towards the other hanging bowling balls.

Crosscutting Concept: Cause and Effect - Students will be able to characterize Newton's Laws as a cause and effect relationship. These cause and effect relationship can be used to make predictions about how the natural world functions.

This demonstration is designed to accompany a unit highlighting Newton's Laws

Demonstrations

1. Newton's 1st Law Demonstration (this lesson)
2. Newton's 2nd Law Demonstration
3. Newton's 3rd Law Demonstration

## Student Demonstration

10 minutes

It is important to craft a demonstration that accurately describes Newton's 1st Law and does not introduce any misconceptions. Newton's 1st Law is often the hardest to explain because it is not what students observe in their everyday life, where gravity is a constant and not thought of as an independent force.

In 1687 Isaac Newton published his book Philosophiae Naturalis Principia Mathematica, or more commonly referred to as the Principia. An English translation would be the Mathematical Principles of Natural Philosophy. Newton's Laws were originally written in Latin and translated, thus explaining the many versions that are taught in school (something that I have found adds to the confusion). I teach one version and remind my students that they will encounter many re-phasings that all have the same meaning.

Newton's Law (version I teach)

1. Objects in motion stay in motion. Objects at rest stay 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.

We discuss in class that an object at rest will stay at rest - forever. The picture of the basketball will stay on the cart forever, unless another force (hitting it) moves it.

Objects in motion is a little trickier to explain, since students observe the opposite. Objects in motion stay in motion, such as a baseball pitch. My students are very quick to counter that the baseball will eventually fall to the ground, which is correct. I immediately have them discuss what caused the baseball to fall and they are able to answer that gravity and wind resistance slows the baseball and causes it to fall. The key to get your students to understand this part of Newton's 1st law is to get them to recognize that gravity and air resistance are 'other forces' that affect the motion of the baseball. We talk about what would happen if we were to travel to outer space, away from Earth's gravity, and repeat the baseball pitch. Most students can visualize a baseball flying through space forever in a straight line.

The example I use in class is a basketball on a moving cart. The basketball is in motion and will remain in motion even when the cart comes to a stop. We also talk about inertia, which is an object's resistance to change. The basketball moves backwards when I first start pushing the car because it resists and forward motion. It also continues moving when the cart is stopped because it is also resisting the stopping force.

## Student Activity

40 minutes

Students will make a foldable pull-out that ties together these three lessons:

1. Newton's 1st Law Demonstration
2. Newton's 2nd Law Demonstration
3. Newton's 3rd Law Demonstration

Each lesson was completed as a separate assignment. All three activities were not finished until all three lessons were completed. This science foldable is based upon Dinah Zike's Science Notebook Foldables. Basic construction can be seen in the following video:

I've added an extra square to make this foldable expand out to three sheets of paper. My students do not pull their foldable out into one large poster, but rather open it up one sheet at a time accordion style. Each square represents one of Newton's Laws.

The students are required to have have a title for each square, use a minimum of three colors, include the actual law being addressed, labels, and an explanation of the example being documented.

Student Work Sample