Newton's 1st Law: Penny on a Coat Hanger - Newton's Law Expo (4 of 9)

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Objective

Students will be able to experiment with Newton's 1st Law of motion using a penny and a coat hanger.

Big Idea

The centripetal force created by a swinging coat hanger will keep a penny pinned to the end of the coat hanger's hook.

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 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: 

  1. Coin Activity (1st Law)
  2. Hammer/Nail Activity (1st Law)
  3. Greek Waiter Tray (1st Law)
  4. Penny on a Coat Hanger (1st Law) (today's lesson)
  5. Ping Pong Ball Activity (2nd Law)
  6. Balloon Racer (2nd Law)
  7. Paper Clip Racer (2nd Law)
  8. Skateboard Activity (3rd Law)
  9. Newton's Cradle (3rd Law)

 

I have also developed three demonstrations of Newton's Laws

Demonstrations

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

With this lesson, students engage in a short (eight minute) activity designed to demonstrate one of Newton's Laws. A penny is carefully balanced on the end of a coat hanger hook. When the coat hanger is spun around, the penny should remain in place. When a force is applied at a right angle to an object, a centripetal force is produced (MS-PS2-2). 

If the penny is balanced correctly, this activity demonstrates that the centripetal force generated will hold the penny in place (PS2.A). It is the student's responsibility to use evidence recorded during the activity to determine that Newton's 1st Law, as it applies to centripetal force, is being expressed (SP7). Each activity has been carefully chosen to replicate a specific effect, anomaly that a balanced penny will remain in place, regardless of opposing forces (CCC).

Set-up

15 minutes

There are some basic materials needed for this activity.

  1. Wire Coat Hanger
  2. Pennys
  3. Drill

Directions for Set-up

  1. Using a wire coat hanger, bend the long straight end away from the hanging hook to form a large diamond.
  2. Drill a small indent into the exact center of several pennies. Be careful to not drill through the penny. 

 

 

 

Print out a copy of Station Markers, and place around the room at the locations where students are to work. 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 4.  

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 First Law of Motion will be in effect for this lesson. Newton's First Law states that an object in motion will remain in motion and an object at rest will remain at rest, unless acted upon by another force. If that force acts at a right angle, the motion observed will be in a circle. This force is known as a centripetal force.

Students do not know what specific law of motion they will be experimenting with. They have to record what they see, gather evidence, make an informed decision and use argumentation to defend their decision about which law is being manipulated.

Directions

  1. Place the coat hanger on the tip of your finger.
  2. Carefully balance the penny on the tip of the hook.
  3. Spin the coat hanger on the tip of your finger.

Explanation

Gravity is initially holding the penny on the end of the hook assuming the penny is carefully balanced. As the coat hanger is spun around a finger, an accelerating force is applied to the penny that pushes it down onto the hook. The circular motion is unrelated to the penny. According to Newton's 1st Law a force is applied keeping the penny in place. This force is applied at a right angle, creating centripetal force. When the force is removed from the penny (spinning has ceased) the penny will travel in a straight line as it is shot away from the coat hanger.

TIP: I would not recommend showing the kids that a penny can be shot from the coat hanger, they'll probably figure it out on their own.

 

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 using this translation of the Laws.

  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:

  1. Newton's 1st Law - Inertia
  2. Newton's 2nd Law - Force and mass determine acceleration
  3. Newton's 3rd Law - Forces act in pairs