NEWTON’S CRADLEThe 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.

EPISODE 1: CRUMBS

NEWTON’S CRADLE

TO TEACHERS AND PARENTSA 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.

OBSERVATIONSWatch 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 ACTIVITYDoes it work wellWhy? 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.

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?

EXTENSION: This activity could be made measurable by using the flicking part of a ballpoint pen to create a consis-tent force. The distance that the last mar-ble 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

CRITIQUING EVIDENCEChildren 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?

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.

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?

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 investigationsInvestigating 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-of-science/What-is-the-Nature-of-Science/Teacher-suggestions-Understanding-about-science/Scientists-think-critically-about-results

http://scienceonline.tki.org.nz/Introducing-five-science-capabilities/Gather-interpret-data

http://scienceonline.tki.org.nz/Introducing-five-science-capabilities/Critique-evidence

Capability focus:GATHER & INTERPRET DATA; What did you see?What might this mean?Which are observations and which are inferences?

CRITIQUE EVIDENCE:How confident are we in the validity and reliability of our method and results?

Activity 14 – 5 of the same ball Rope (eg: clothesline type)Bungy cords or cable tiesOptional: much harder balls (eg: petanque)

Activity 2Grooved metre ruler or 2 plain onesBlu tackMarblesBall point pen

MATERIALS

NZ CURRICULUM PLANNING SUMMARY