Plastics: how to make the right choice

There is no ‘one size fits all’ plastic, and some plastic types are better suited for specific tasks than others.

TABLE SHOWING CHEMICAL RESISTANCE PROPERTIES OF VARIOUS PLASTICS USED IN SCIENCE.

SUMMARY TABLE OF RESISTANCE FROM WORST PERFORMING PLASTIC (RED) TO BEST (GREEN).

Resistance to acids:

Resistance to organics:

For more useful help with selecting the right plastic for the job, download our physical properties of plastics table here

Static electricity!

A fun activity introducing static electricity, something pupils will explore later in the curriculum

EQUIPMENT: (per group)

• Balloons, pre blown up

• Small pieces of paper

• A plastic or acetate rod

• Duster

• Tap with running water

• Paper boat

• Shallow tray

• Bubble mix and straws

• Large tile or smooth surface (lab bench)

METHOD:

1. Pick up the plastic rod and touch it to your head.

2. Using the same rod, touch it to some small pieces of paper.

3. Now hold the rod close to a thin stream of water.

4. What do you observe?

5. Now rub the rod vigorously with the duster and repeat steps 1, 2 and 3. What do you observe this time?

6. Take the pre blown up balloon, rub it on your head and gently pull it away. The hair should cling to the balloon.

7. Using the same balloon, after rubbing it on your head (or on a jumper) repeat steps 2 and 3, and see what happens.

8. Swap out the small pieces of paper for small polystyrene packing beads and (after rubbing with a duster) bring the rod or balloon close to them.

Extension

• Make a small paper boat and put it into a shallow tray of water, use the rubbed rod or balloon and see if you can move the boat without touching it.

• For a similar effect try it with a paper windmill: fold a small square of paper into four to find the centre point, balance this on the pointed end of a pencil held in place on the desk and use the rubbed balloon/rod to try and spin the paper ‘windmill’ without touching it.

• Add some bubble mix to the tile, using the straw blow a bubble in the mix, but don’t lift the bubble from the tile. Bring the rubbed balloon close to the bubble. What happens?

THE SCIENCE BIT…

When the plastic of the balloon or rod is rubbed with a duster or your clothes (or even hair) the balloon/plastic rod will gain electrons and become negatively charged, the material you rubbed it with will lose electrons and become positively charged. The electrons have moved from the cloth to the balloon.

Now that the balloon is charged it will attract the opposite charge of anything it touches or comes close to. Therefore, it will attract them and make them move.

Using the extension activities will encourage further thinking about same charges repelling.

Although electrons will not necessarily have been visited by year 6 students, they will have met the forces of attraction and repulsion with magnets, so charged objects causing movement will have been seen before.

WHY DO WE COVER OUR MOUTHS WHEN WE SNEEZE OR COUGH?

We have all experienced the COVID pandemic, where we were asked to wear masks so that we didn’t ‘breathe on people’, and to sneeze into our elbows so that we didn’t transfer ‘germs’ to other people on our hands. But why?

In this practical you can demonstrate the effect ‘blocking’ has on the distance a ‘sneeze’ would have travelled, and thus help to halt the spread of (airborne) disease.

EQUIPMENT: (per student group)

• Several large sheets of paper

• Two clamp stands and a metre rule (or long stick)

• A spray bottle containing very dilute food colour in water

• Some tissues

• Gloves (or a cutout of a spread hand, on a stick)

• Measuring tape or rulers

METHOD:

SET UP:

Set up the apparatus, with the two clamp stands and metre rule (or long stick) holding a sheet of paper, with more paper covering the bench.

1. Student 1 stands at the end of the bench facing the clamp stand arrangement, with the spray bottle.

2. They spray once towards the paper hanging from the ruler.

3. Student 2 measures the distance and width of the coloured spray on the paper and writes it down.

4. The 2nd (or 3rd) student then holds the ‘hand’ cutout (or their own gloved hand) in front of the spray bottle.

5. The 1st student sprays the coloured water again, and the 2nd student writes down the distance and width that the spray reached on the paper.

6. This process can be repeated holding a tissue in front of the spray bottle (to mimic real life).

7. You can repeat the process using specified distances to see how close the hand or tissue needs to be to stop any spray going past it.

Questions to ask

Did the distance of the hand make any difference to the distance of spray, or the width of the spray?

Could they draw a graph of distance of spray versus hand distance from student 1?

How effective was the hand or tissue in stopping the width of the spray?

This is a nice way for the students themselves to see how effective a tissue, or a hand, is in stopping the spread of microbes contained in saliva when a person sneezes, or coughs. Although it would be a stretch to introduce the role of bacteria, yeast, ‘good’ and ‘bad’ microbes at this level, it would be a nice experiment to return to when that topic is visited later in Year 7 or 8, alongside the handwashing practical. It can also be used as a graph drawing exercise, as another skill provision.