Idea 4of 6Builds onTwo arrows, one pathNaming a direction
Measured, not calculated
No calculator. Can a ruler find the resultant?
Today you'll discover
- how a ruler can add two legs at any angle
- what the little scale bar in the corner is for
- why you measure the one arrow instead of working it out
Think firstA map's corner says one centimetre stands for five kilometres
An arrow on that map is 3 cm long. How far does it stand for?
Decide first, then press Next. Watch the scale bar, and read the ruler on the one arrow.
A compass rose and a scale bar reading one centimetre for five kilometres. After a prediction, a ten-centimetre arrow is drawn west and a twenty-centimetre arrow is drawn from its head at an angle; then one arrow from the first tail to the last head is drawn with a ruler laid along it, reading about seventeen centimetres. The last step shows a resultant of one point seven centimetres on a map with a different scale.
See the whole ideathe big idea and the key word, in one place
The big idea
A scale diagram: draw to scale, measure, multiply by the scale.
Compare themMeasured: a ruler on the drawing, honest to about half a millimetre. Calculated: components added and rebuilt, honest to the last digit. Both give the same resultant; a test may ask for either.
Key word
- scale diagram
- a drawing in which every vector's length is its size times a stated scale and its angle is true, so the resultant can be measured with a ruler and a protractor
About this modelArrows are drawn to the scale in the corner; a bearing turns from north (or east).
Arrows are drawn to the scale in the corner; a bearing turns from north (or east).
Ready to use it?
- Convert a measured length on a scale diagram into the resultant's size.