Density – observation and inference
John Marsh is a science teacher at Tauranga Intermediate School. John and his students observe what happens when Skittles candies interact with warm water. After observing the interactions, the students make inferences regarding the different colour coatings and layering.
Questions for consideration
How do you define observation?
How do you define inference?
What is the difference between observations and inferences and why is this important?
Is a prediction the same thing as an inference?
How might John’s follow-on experiments influence the students’ inferences if they revisited this activity?
Transcript
John Marsh
We are going to do an experiment that is going to look at observation and inference.
Here are the Skittles. We’ve got a purple one, a green one, a red one and a yellow one. OK, and we’re going to put them equidistant here. We’re going to add some warm water.
Have a quick discussion and make some predictions.
What do you think is going to happen next?
Have some guesses.
Students
I think when the water gets put in, I think the colours from the Skittles will come out and go into the water.
Yeah, and I think they might like merge together and then like make cool colours.
Yeah.
John
Do you think one colour would melt or do, change faster than another?
Students
I think maybe the green or the yellow.
Because they’re lighter colours.
Yeah.
John
OK. So shall we try?
Student
Yeah.
John
OK, can you set up the experiment please?
Students
The green and the yellow …
Look at the red though …
Oh, that one, that one’s like …
That one I think has the most colour coming out of it.
Yeah, I don’t think the yellow has much coming out.
Yeah, but look at the green and orange.
Yeah, that’s pretty cool.
The colours are slowly going into the middle and it’s merging more in the middle.
John
How do you think they are merging? Are they, um, kind of going like that or are they going over the top?
Students
I think the, the purple’s going underneath the light colours, it looks like.
Yeah.
The yellow and the red are going over it.
John
So how do you think a scientist would explain this?
Student
Maybe it’s for the different particles. They have different particles and when they come together, they join differently.
John
They join differently, OK.
Student
Maybe it’s the water that’s making the colours merge differently. And the green has less on the top than the others.
John
So it sinks to the bottom, do you think?
Student
Yeah.
John
OK, so which one, which colour do you think sinks the best?
Student
The green, probably.
John
Probably.
Student
And it kind of looks like the …
John
So if the green is sinking.
Student
Yeah.
John
What could you say about the green particles compared to red particles?
Students
The green particles could be like a little bit heavier than the red particles.
Yeah.
I think it’s maybe because the weight of the colour has made them group together more.
John
OK.
My next move would be to do two more experiments – one looking at two different densities of liquid such as golden syrup and water and observing those in the glass when they meet.
And the second one would be getting two glasses, one with a tablespoon of salt, one with a tablespoon of sugar – two quite distinctly different sized particles – and seeing which dissolves.
And with those observations and the learnings from that, revisit this experiment and see if different conversations will happen.
Acknowledgements
The Science Learning Hub Pokapū Akoranga Pūtaiao acknowledges the contribution of John Marsh, Tauranga Intermediate School, and the New Zealand Association of Primary Science Educators (NZAPSE) in making this video.
New Zealand Association of Primary Science Educators
New Zealand Association of Primary Science Educators (NZAPSE) logo.
