Page 90 - 6748

onto the end of the bottle, at the top, to form a nose. It didn’t go exactly according to plan, at
first. It stabilised it a bit, but it still wasn’t flying straight. So we tried putting water in the
beaker, to act as ballast, and that worked a treat. With the extra inertia, and the fact that it was
front- heavy, it went like an arrow. So, so, yes, we sorted that problem out. Then the next goal
was to increase the power, to try and reach a higher altitude.

c ► 9.4 Listen again and complete the following phrases from the description.
1 (as expected) It didn't go exactly
2 (extremely well) It worked

10a In pairs, discuss possible ways of making the water rocket more powerful to
allow it to attain higher altitudes. The basis of the design should be the same and you may
only use basic materials. For each solution, explain the following points.
1 Why you would expect the rocket to be more effective
2 Any potential problems
b 9.5 Read Manfred describing how the rocket was developed and the results of further
tests. Make notes on the improvements made and their consequences. How do the solutions
compare with your ideas from Exercise 10a?

Manfred: One of the things we did was to experiment with the amount of water inside the bottle.
I think, initially, we expected that the more water we put in, the more powerful it would be. But
as it turned out, it was the opposite.
What actually happened was, if you overfilled it, there wasn’t enough pressure to expel all the
water. We reduced the amount of water to about a quarter or a third full, something like that,
and we also put some tape around the end of the pump, to get a better seal with the bottle. That
was really effective. I think we underestimated the pressure we were generating. And, certainly,
we were overestimating the strength of the bottle. Because it got to the point where we were
firing these rockets up to, I don’t know, maybe something like 20 metres high, something like
that, so you can imagine the sort of pressure involved. And plastic bottles are hardly up to the
job of high-pressure rocketry, obviously. So, inevitably, the bottle eventually blew up while I was
holding it. I was rolling around on the ground with sore hands, while everyone else was rolling
about laughing. So I learned the hard way.

c Read the following phrases that Manfred uses. Complete the definitions by underlining
the correct words.
1 as it turned out = what happened in theory/practice
2 what actually happened = what happened in theory/practice
3 we underestimated the pressure = it was less/more than we thought
4 we overestimated the strength = it was less/more than we thought
5 plastic bottles are hardly up to the job = they’re adequate/inadequate
6 I learned the hard way. = it was a theoretical/practical lesson

d In pairs, discuss the following questions.
• Did you have any experiences of building things when you were younger which didn’t
turn out as you’d expected? What did you underestimate or overestimate? What lessons did you
learn the hard way?
• When you were younger, what experiences were most beneficial in helping you to
improve your technical skills? What technical principles did you learn?

11 Amateur rocket scientists have produced water rockets capable of reaching altitudes of
several hundred metres in competitions. In pairs, think of initial ideas for a suitable design

88