Video Transcript
Seconds are used to measure a short
period of time. Complete the following: In the
given activity, jumping jacks take what seconds.
This question is all about how long
it takes to do some jumping jacks. These are a great form of exercise,
but you probably wouldn’t want to be doing them for too long. Perhaps that’s why, in this
question, the activity’s been measured in seconds. As we’re reminded right at the
start here, seconds are used to measure short periods of time. And we need to find out how long
these jumping jacks have taken. To help us complete this sentence
and find how long these jumping jacks take, we’re given three stopwatches. Or really, as we’re going to find
out, it’s the same stopwatch but shown three times.
The first stopwatch is labeled
start time. This shows us what the stopwatch
looked like when the activity began. And if we want to work out how long
something’s taken, we need to know when it started. Our second picture shows us what
the stopwatch look like at the end of the activity. Knowing the end time is just as
important as knowing the start time with a question like this. Our final picture really just puts
these two facts together. The part shaded blue shows us where
the hand on the stopwatch has moved. We can see both the start time and
the end time. And it’s this third picture that’s
probably going to be most useful to us. It shows us exactly how long the
activity’s taken or, if we want to use a mathematical word, its duration.
We can see that the hand on the
stopwatch started when it was pointing directly upwards at the number 60. There are 60 seconds in one minute,
and that’s all the way around the clock face. So we really can think of this
clock face as going from zero all the way around to 60 seconds. And when the second hand points to
this number at the very start, it’s not pointing to 60, but really to zero. This is really useful to us. Because we’re starting at zero, we
just need to look at the end time, and this will tell us how long the activity’s
taken. If we look at the end time, we can
see that the second hand has moved just past the number 35. There are five seconds between each
number on the clock face.
But these are all labeled, so we
don’t need to start at zero and count in fives. We can just go straight away to 35
and then count on. Looks like we’re going to have to
count on another two more seconds. So we’ll say 35 and then 36,
37. In order to find out how long
something lasts or its duration, we need a start time and an end time. We’ve read both the start and the
end times on our stopwatch. And we’ve used these to find out
the duration of the jumping jacks activity. In the given activity, jumping
jacks take 37 seconds.
