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Transcript
EPISODE 1: CRUMBS
NEWTON’S CRADLE
TO TEACHERS AND PARENTS
A large focus in teaching science is around encouraging both curiosity
and the skills and dispositions to be able to find out or test things for
yourself. This includes developing an understanding about how science
itself works. The New Zealand Curriculum calls this the Nature of Science.
Tips about how to encourage these aspects are given in a
Use these to get your children talking, discussing, testing and thinking
about the science involved in Jiwi’s Machines. Have fun! The science
content involved in Jiwi’s Machines relates to the Physical World
Achievement Aims of the New Zealand Curriculum.
NEWTON’S CRADLE
The Newton’s Cradle is a terrific way of demonstrating some key ideas about
energy and motion.
The Law of Conservation of Energy says that energy cannot be created or
destroyed. It can however change forms.
In Jiwi’s NEWTON’S CRADLE CLIP you can see this as the first ball is lifted and
held. It gains gravitational potential energy. This means it has an amount of stored
energy. How much energy it has relates to the object’s mass and how high up it is.
When the ball is dropped, the energy is changed into a moving, kinetic energy.
As the moving first ball hits the stationary second ball, all of its energy is
transferred into ball 2 and ball 1 is now stationary. This transfer of energy continues
directionally from ball 2 to 3, ball 3 to 4, ball 4 to 5. When the last ball gains the
kinetic energy, it is able to move and swings to its highest point. It is losing kinetic
energy as it goes but this is being transferred into potential energy until it has no
more moving energy but lots of potential energy.
For a split moment it has zero kinetic energy and all potential energy before it
swings in again, gaining kinetic energy and losing potential energy. You should be
able to see the ball slowing as it reaches its highest point before it falls again and
picks up speed before bumping into the next ball.
OBSERVATIONS
Watch Jiwi’s clip again and watch closely
What did you see?
What might this mean?
Which are observations and which are inferences?
Can the children describe the flow of energy through
the balls? Do they notice the slowing of the last ball
as it swings high, coming to a stop, then speeding up
again as it falls? Think, pair, share.
A negligible amount of energy is also transferred to heat
energy through friction between the balls and in air resistance
The Law of Conservation of Momentum means the momentum lost by object 1
is equal to the momentum gained by object 2. In this way, momentum (the force
of objects in motion) is also conserved as it passes from one ball to the next and
back.
BRAINSTORM: Where else in life might we see this idea that energy and
momentum are conserved?
HINT: The firing of a catapult or rifle. Other ideas?
ACTIVITY 1:
(ONE HOUR)
BIG SCIENCE IDEA: Energy is not lost;
it changes forms.
Construct a larger than life Newton’s
Cradle using sports balls on your
playground.
It is important that each ball hits the next
ball cleanly. You could use bungy cords,
cable ties or even a tightly tied sling made
from cut up plastic supermarket bags.
The thin rope needs to be tied slightly
down from the top on each side of each
ball.
For best effect and most fun you need a
minimum of three balls. More is better!
Start as Jiwi did by lifting one ball and
releasing it.
NOTE: as these balls are very elastic a lot
of energy is lost in elastic “bounce”.
You should be able to get two or three
“swings” out of this activity. Encourage the
children to think about why this does not
work as well as Jiwi’s exercise. What type
of balls may work better? Try again with
petanque balls.
CRITIQUING THE ACTIVITY
Does it work well
Why? Why not?
What could you change to
improve it?
Have a go!
JIWI WONDERS
• Why did the ball at the far end
swing out?
• What was happening to the balls
• in between?
• What else would you like to try?
ACTIVITY 2:
(10 MINS)
BIG SCIENCE IDEA: Energy is not lost; it
changes forms.
BIG SCIENCE IDEA: The force of an object
in motion is not lost but passes to the
object it hits.
EXTENSION: This activity could be
made measurable by using the flicking
part of a ballpoint pen to create a consistent force. The distance that the last marble moves can then be measured. Repeat
measurements can be made to make the
data more reliable.Measurements of other
combinations can be made also.
For more explanation and information visit:
http://science.howstuffworks.com/newtons-cradle.
htm
Using a grooved metre ruler or a channel
between two metre rulers side by side,
place two marbles so that they are
touching each other some distance in.
CRITIQUING EVIDENCE
Children can be encouraged
to ask and answer such questions as:
How sure are you of your results?
How did you get the data?
What were the possible
shortcomings of this method?
How could you check your findings?
How many times was the
experiment repeated?
How were the measurements
taken and recorded?
How confident are you that the
measurements are accurate?
Did these results surprise you?
What were you expecting to find out?
Would these results always be true?
It may pay to blu-tack the two rulers in
place. Place one more marble at the end
closest to the lined up marbles and flick it
along the channel.
What do you observe?
Why does this happen?
What would happen if you put three
marbles in the middle? Four? Or more?
What else would you like to try?
Can you describe what is happening to the
energy in this activity?
JIWI WONDERS
• What will happen if I flick two
touching marbles at the line-up
• of marbles?
• What will happen if there is a gap
between some of the marbles in
• the line up?
• How could you make this activity
measurable?
MATERIALS
Activity 1
4 – 5 of the same ball
Rope (eg: clothesline type)
Bungy cords or cable ties
Optional: much harder balls
(eg: petanque)
Activity 2
Grooved metre ruler or 2 plain
ones
Blu tack
Marbles
Ball point pen
NZ CURRICULUM PLANNING SUMMARY
Contextual Achievement Objective:
PHYSICAL WORLD; Explore and investigate
physical phenomena in everyday situations.
Nature of Science Achievement Objective:
Understanding about Science; Scientists think
critically about the results of their investigations
Investigating in Science; Students’ investigations
have the potential to be reconsidered, debated
and developed further.
Big Science Idea: Energy is not lost, it changes
forms. The force of an object in motion is not
lost but passes to the object it hits.
Big Nature of Science Idea:
In science we need to critique our methods and
ideas.
Weblinks: http://scienceonline.tki.org.nz/Nature-
Capability focus:
GATHER & INTERPRET DATA;
What did you see?
What might this mean?
Which are observations and which are
inferences?
of-science/What-is-the-Nature-of-Science/Teachersuggestions-Understanding-about-science/Scientiststhink-critically-about-results
http://scienceonline.tki.org.nz/Introducing-fivescience-capabilities/Gather-interpret-data
http://scienceonline.tki.org.nz/Introducing-fivescience-capabilities/Critique-evidence
CRITIQUE EVIDENCE:
How confident are we in the validity and
reliability of our method and results?