Idea 10of 11Builds onHow fast, on the path
The same speed, two units
A road sign and a graph: do they agree?
Today you'll discover
- what a road sign's unit means in metres and seconds
- the one number that crosses between the two units
- when two readings need no converting at all
Think firstA cart holds a steady 6 m/s
The cart's line sits at 6 m/s. On a road sign, in km/h, about how much?
Decide first, then press Next. Watch the same flat line read in two units.
The cart's velocity–time graph, a flat line at six metres per second for four seconds. After a prediction, the line is read as 21.6 kilometres per hour, then a sign's 100 kilometres per hour is turned into 27.8 metres per second. The last step asks about a car slowing from 100 to 50 kilometres per hour.
See the whole ideathe big idea and the key word, in one place
The big idea
Kilometres per hour, over 3.6, is metres per second.
Easy to get wrongConvert before any equation that mixes units. A ratio of two readings in the same unit needs no converting at all.
Key word
- kilometres per hour
- a speed unit, km/h: how many kilometres each hour; divided by 3.6 it is metres per second
About this modelBelow the line means moving the other way, not slowing down.
Below the line means moving the other way, not slowing down.
Ready to use it?
- Convert a speed between km/h and m/s before using it, or say why no conversion is needed.