Why ice floats on water Ice floats on water because it has a lower density than water. When water freezes, the molecules in it move further apart from each other and therefore the frozen water (ice) takes up more space. The ice still has the same mass as when it was water, but the volume has now increased. Therefore its density is now less than water.
Fig. 4 Penguins on a floating iceberg. 28.2 Speed
The speed of an object is the distance travelled per unit time. The unit of time is 1 second (s). The unit of speed is m s-1
(m/s or metres per second) The world’s fastest sprinters can run 100 metres in 10 seconds. The
The speed of an object is the distance travelled per unit time.
average speed of the sprinter is found by dividing the distance travelled by the amount of time taken:
Speed =
Distance Time
=
100 m 10 s
= 10 m s-1
Fig. 5 Usain Bolt holds the record for being the fastest human, running at a speed of 44.7 km/h (12.4 m s-1
Distance versus Time graphs This table gives the figures for an athlete running 100 m.
Time (s) Distance (m)
0 0
2 20 4 40 6 60 8 80 10 100 We can now plot a graph of distance against time, putting time on the horizontal (x) axis.
