PHY ICS - The Institute of Physics in Ireland
PHY ICS - The Institute of Physics in Ireland
PHY ICS - The Institute of Physics in Ireland
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6 forces<br />
Water rocket<br />
Austria<br />
Break<strong>in</strong>g surface tension<br />
You will need...<br />
✔ a bowl <strong>of</strong> water<br />
✔ some card<br />
✔ a pair <strong>of</strong> scissors<br />
✔ some wash<strong>in</strong>g-up liquid<br />
Background<br />
Some small <strong>in</strong>sects can walk<br />
on the surface <strong>of</strong> water ow<strong>in</strong>g<br />
to surface tension.<br />
Follow these steps<br />
1 Us<strong>in</strong>g the template shown,<br />
cut out a paper rocket.<br />
2 Place the rocket onto the<br />
surface <strong>of</strong> the water.<br />
3 Put a drop <strong>of</strong> wash<strong>in</strong>g-up<br />
liquid <strong>in</strong> the central circle <strong>of</strong><br />
the rocket (dip a pencil <strong>in</strong>to<br />
the detergent then dip it <strong>in</strong>to<br />
the water <strong>in</strong>side the circle)<br />
and watch what happens.<br />
<strong>PHY</strong>S<strong>ICS</strong> ON STAGE 3<br />
water rocket<br />
detergent<br />
So what happened?<br />
When the detergent is added<br />
it locally reduces the surface<br />
tension <strong>of</strong> the water. Ow<strong>in</strong>g<br />
to the shape <strong>of</strong> the card, the<br />
rocket shoots forward.<br />
What next?<br />
Try repeat<strong>in</strong>g this exercise<br />
several times <strong>in</strong> the same<br />
water. You will f<strong>in</strong>d that it<br />
only works two or three times<br />
before there is too much<br />
detergent present. Add<strong>in</strong>g<br />
more has no effect – now the<br />
surface tension is low all over<br />
the surface.
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