Newton's Third Law Of Motion

Lilla E. Green                 Hartigan Elementary School
                               8 West Root Street
                               Chicago IL 60609
                               (312) 535-1460

Objective:

  This mini-teach is designed for grades 4 - 6.  Pupils will verbalize and 
demonstrate Newton's 3rd Law of Motion:  action and reaction. 

Materials Needed:

These materials will be used for teams of five - six pupils. 

string
tape
long party balloons
straws (milkshake size)
masking tape
scissors
empty soda pop can with the opener lever intact
nail
bucket/tub of water
11 x 14 piece of cardboard
marbles
ten foot nylon rope
wind-up Tomy truck
giant skateboard (about 20 ft.)
timer (clock)
two demo spring scales
fan cart (Pasco dynamics cart w/ personal face fan attached)
three foot skateboard

Strategy:

Rocket Launch:
 Have four - five pupils attempt to get balloons across the room.  Some may 
throw them across, blow them up and release them, or walk them across the room.  
Lead them to realize that they need a direction for their balloons.  Now, have 
pupils inflate balloons as a team and launch them in races.  The balloons slide 
along the strings on the thrust produced by escaping air.  Then pupils discuss 
what happened and try to give reasons for what they observed.  Next, teams 
travel through four stations which reinforce the idea of action/reaction.  The 
stations are described below: 
     
Stations                         Activities
(1)                        Soda Pop Can Hero Engine - Pupils observe water 
                         streaming through 4-6 holes (made by a nail) in the 
                         bottom of a suspended soda pop can.  The water causes 
                         the can to rotate in the opposite direction from the 
                         direction of the streaming water. 
(2)                        Three foot skateboard - Pupils line up and step up on 
                         the skateboard, one at a time.  As the pupils step off
                         the skateboard, they are to observe what happens.  
                         Safety Note:  Have someone hold their hand as they 
                         step off the board.
(3)                       Truck and Marbles - Pupils space about 20 - 25 marbles
                         evenly under a 11 x 14 square cardboard.  Then a Tomy
                         wind-up truck is placed carefully on the cardboard.
                         When the lever is released, the pupils are to observe
                         what happened.
(4)                       Demo Spring Scales - Pupils pair off and hook one demo
                         spring scale to the hook of their partner's spring.  
                         One tries to pull with a force of 4 Newtons while their
                         partner tries to pull at a force of 8 Newtons.  Pupils
                         will describe the situation and tell what happens and
                         why.

Groups rotate every four minutes (teacher uses the timer to keep groups on 
task).  At the end of the sixteen - twenty minutes, each group nominates a 
reporter to share the findings of their team.  

As a closing activity, pupils play "Tug Of War" using the giant 20 foot 
skateboard.  First, pupils pair off and join hands with their partners.  A piece 
of masking tape marks the starting off position.  Whichever partner comes over 
the tape, loses the round.  Next, have a person with a small physique go against 
four larger people using the nylon rope, which is looped at both ends. 
Naturally, the small pupil loses.  Then have the four larger pupils stand on the 
giant skateboard, and have pupils predict the outcome of the tug of war.  The 
class discusses what happened and why.  Then a general rule or law is produced 
through total group participation. 

Assessment:

Groups write up their thoughts about each station and post their group's 
conclusions on the chalkboard.  Selected persons report orally before the class.

Conclusion:

Fan Cart:  Attach a personal fan to a Pasco dynamics cart with tape.  Turn it 
on. The class concludes that the action of the blades on the fan is the cause of 
the cart gliding in the opposite direction.  This gliding is the reaction force.  
Pupils form the general law which states that actions take place in pairs with 
reactions.  For every action, there is an opposite (and equal) reaction.  For 
example, with the Hero Engine, water streams in one direction and the can 
rotates in the opposite direction.  With the truck and marbles' activity, the 
truck goes in one direction while the cardboard goes in the opposite direction.  
As the person steps off the skateboard, they exert an action force on the board, 
making it go in the opposite direction.  Pupils found that they could not pull 
on opposite ends of the Demo Spring Scales with different amounts forces.  As 
they pulled, the scales always read the same force.  In every activity, pupils 
conclude that whether a balloon is racing along a string, or whether one is 
engaged in a tug of war, there will never be an action force exerted without a 
resulting reaction force. 

References:

New Explorers:  "Endeavors/Mae Jemison"
Globe's: Concepts and Challenges -  Physics
E-mail address  lgreen@teacher.acs-lc.depaul.edu