What is Required to Keep Something Moving?

School of the Future, Manhattan

Summer Research Program for Science Teachers

August 2012

Subject: Regents/General/Conceptual Physics

Time Frame: 2-3 Periods

Objectives:  By the end of the lesson,

• CONTENT: Students Will Understand That:
• No force is required to keep an object moving.
• (Unbalanced) Forces are required to change the motion of an object.
• SKILL: Students Will Be Able To:
• Articulate Newton’s First Law (N1L) of Motion.
• Use N1L to make predictions and explanations about the motion of objects.

Materials Needed:

• Air Glider & Track
• Hard Boiled Eggs & Raw Eggs
• Pennies
• Balloons
• Plastic Spiral & Marble
• Inertia Boxes (Empty Boxes and Large Masses)
• Cups
• Index Cards
• Dry Ice
• Nail
• Spring

Motivation:  Through demonstrations and hands-on activities, students are challenged in their belief about what is necessary to keep something moving.  They are introduced to Newton’s First Law of Motion and given the opportunity to use it to make predictions and explanations.

Push Up (Do Now):

1.      In their notebooks, students write down and answer the following questions.  For each, give an example to support your claim.  (8 Minutes)

a.     What is required to keep something moving?

b.     What is required to change the motion (velocity) of something?

2.      Share out ideas in groups.  Give students a chance to revise their thinking based on their peer’s arguments.

Flow of Lesson:

1.      Motion Glider Activity (15 Minutes)

a.      Call students up to the front of the room and let them see the air track.

b.            Turn it on and let them feel the air coming out of the track.  You can put the glider on the track but do NOT push it!

c.            Predictions:

i)       Question 1:  What must be done to get this glider moving?

ii)     Question 2:  After it has been put in motion, with the air track off, what will happen to it?  Why?

iii)  Question 3:  After it has been put in motion, with the air track on, what will happen to the glider?  Why?

d.          Observe:

i)       Record all observations for each of the scenarios described in the positions.

e.           Explain:

i)       Why do you think you observed what you did (for each prediction question)?

ii)     Question 4: If the track was infinitely long and all of the air could be sucked out of the room and the track was perfectly frictionless, BASED ON THE TREND OF LAST TWO OBSERVATIONS, what will happen after it has been put in motion?  Why?

f.      Class Discussion:

i)       Discuss observations and explanations for first three questions and the thought experiment from Question 4.

ii)     Goals:

(1)   Elicit the idea that a force is a “push or pull” from an external source.

(2)   A force is required to get something moving or stop something moving.  This can be generalized to a force is required to change the motion (velocity) of an object.

(3)   Nothing is required to keep an object moving.

(a)   Normally, things slow down due to unseen sources of friction.

(b)   If no external forces impede the motion of an object, it will continue moving naturally in a straight line at a constant speed.

2.      Revisit Push Up:  In their notebooks, students rewrite and answer the Push Up again.  (5 Minutes)

a.      What is required to keep something moving?

b.     What is required to change the motion of an object?

3.      Introduction to Newton’s First Law (8 Minutes)

a.      Newton’s First Law of Motion:  An object at rest has a natural tendency to stay at rest.  An object in motion will continue moving in a straight line at a constant speed.  This will continue until it experiences an unbalanced, external force.

b.      Brief Class Discussion: What is a law?  How is it different than a theory?  Is it proven?

4.      N1L Stations Activity  (40 Minutes)

a.      Explain to the students that they will be exposed to five different stations and will make predictions, record observations, and then explain the observations using N1L.  This will eventually be used to create a counter argument. Distribute N1L Stations Handout.

b.      Demonstrate to the students what they will be doing in each of the stations.

i)       Remind them to tape in the little strip of paper with the questions before they do anything.

ii)     Remind them that they MUST record all predictions before actually doing the demo.

iii)  Remind them that they will be constructing this argument from their notes so they better take very clear notes.

c.            Students get 7 minutes per station.

5.      Dry Ice Demo (10 Minutes)

a.           PREP:  Wash and wax a long surface (such as the front lab bench and the floor in front of it).

b.           Give a small piece of dry ice to each student and tell them to give it a push and send it sailing across the floor.  Ask them why it doesn’t slow down as quickly as a toy car would.

i)       Sublimating CO2 creates a cushion that the dry ice coasts along, reducing friction from the floor (but NOT from air).  Friction from air slows it down over time though.

c.            Show them the large block of dry ice with a nail in it.  Tell them you are going to attach a spring to the nail and pull the block of dry ice by the spring.  You are going to pull it with a constant force by making sure that the spring stays stretched the same amount the entire time.  Have them write down the following in their notebooks before starting:

i)       Predict:  How do you think the block of ice will move as the teacher pulls it with a constant force?

ii)     Observe: What happens?

iii)  Explain:  Why did this happen?  Explain using N1L.

d.          Give students five minutes to write down observations and explanations.

6.      Class Discussion (18 Minutes)

a.           Each group records the observations and explanations of one station (including the Dry Ice Demo) on a whiteboard (3 Minutes)

b.           Each group gets 3 minutes to explain the observations and explanation for that station.

c.            Students can revise answers based on presentations and class discussion.

d.          Have one student lead the discussion/presentations and make note of which students still possess misconceptions about motion and/or Newton’s First Law of Motion.

Homework: