Measuring growth
The instrument used to show the growth of a plant is the auxanometer.
Activity 04
Take a plant growing in a pot, tie a thread to its shoot tip, pass the thread over a pulley and hang a weight from the far end. As the plant grows the thread slackens, the weight descends and the pulley turns.
Figure to be added
Observation
The plant grows very slowly, but the pointer attached to the pulley shows that amount of growth on a large scale.
What the instrument actually does
The auxanometer does not speed up growth — it magnifies it. When the plant grows by a millimetre the pulley turns through a small angle, and the tip of a long pointer travels several centimetres across the scale. A change too small for the eye becomes a change that can be read.
This is a common trick in measuring instruments: turning a small input into a large output.