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quite high, there’s a danger the container will roll over and bounce along when it touches down.
In fact, if you’re dropping from low altitude, that’s probably inevitable. So if the container rolled
and bounced for 50 metres, or whatever, then you’d have to have some kind of destructible
external envelope to protect it from the multiple impacts. Which would be very expensive. So,
arguably, rolling is the worst problem, worse than a high vertical impact speed.
Jenna: Hm, you think so?
Arnaud: So you don’t think rolling’s a bad thing? Jenna: I’m not convinced the container would
actually roll.
Arnaud: No?
Jenna: Not necessarily. The military drop tanks out of flying aircraft at low level, tied to special
platforms, and they just slide along the ground. And the systems that eject things out of the backs
of planes are incredibly powerful. So because, obviously, they fire the container in the opposite
direction to the plane, that reduces the groundspeed. Plus, they use a parachute that deploys
horizontally, which also helps to slow it down.
Arnaud: Of course.
Jenna: So, based on what they do with tanks, I think we can safely assume that we can stop a
container from rolling.
Arnaud: But a tank's got massive weight, and a low centre of gravity. With a smaller, lighter
container, there’s no way of knowing how it would behave, not without actually testing it. And
even if you tested it ten times, it would probably behave differently each time, it would be very
unpredictable. Whereas if you drop from a higher altitude, OK, the vertical speed is higher, but
with a lower groundspeed, it would behave more predictably. And that would make it easier to
design a cushioning system because you’d be dealing with a single, predictable impact.
Jenna: Yes, but surely, a heavy vertical landing is a huge problem. The force of it would be far
greater...

5a Rephrase the words in brackets to complete the following extracts from the
conversation.
13 So, (in theory), the horizontal speed will keep decreasing ...
14 So, (assume) the drop altitude's very low, ...
15 ... (sure) a low vertical speed is the critical factor.
16 Because, (presume), if the groundspeed's quite high, there's a
danger the container will roll...
17 So, (argue), rolling is the worst problem, ...

b Rephrase the words in bold in the following sentences using the words in Exercise 5a.
1 I suppose there’ll always be a certain amount of groundspeed.
2 If we assume the container will roll, we’ll need to protect it accordingly.
3 According to the hypothesis, groundspeed will almost always be positive.
4 You could say that it’s inevitable the container will roll and bounce along.
5 I’m convinced that high vertical speed is less problematic than high groundspeed.

c In pairs, decide whether the following words and phrases are used to agree or disagree.
Can you think of other phrases for agreeing and disagreeing?
Absolutely; I’m not convinced; I’m not so sure; Not necessarily; Of course;
True;

d Look at the diagram and, in pairs, discuss the following questions.

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