Here’s a problem. 2 + 3. When your young, I mean very young you learn to count using your fingers and in some cases your toes if you have odd parents. It is said that there are no bad pupils only bad teachers. I’ve had a few lousy teachers in my time and believe me I have lost
a more than a few percepts and concepts on the way. Using fingers, 2 fingers plus another 3 fingers results in 5 fingers. That was pretty straight forward.
Consider this problem 2 + ? = 5. Imagine you are 7 or 8 years young. As an adult you instinctively say 3 but how did you get to the answer? I was faced with this problem and a 7 year old. The ? is the missing amount. What transpired after a long time was the equal sign was not understood. A missing percept. It was never explained. Using fingers one can explain that the one hand has 5 fingers and by holding up 2 fingers on the other hand you can ask the question : How many fingers must I raise to make them equal. Problem. The youngster had lost half of one finger due to a snake-bite. How many people do you know that can count in fractions?
TIME - SPEED
There are 60 seconds in a minute, 60 minutes in an hour and therefore 3’600 seconds in an hour. To get an idea of speed we need distance or length. REMEMBER, THERE ARE 1’000 METRES TO A KILOMETRE. Most of us speak of kilometres per hour. In the farming community they speak in terms of metres travelled in a certain number of seconds or very rarely in metres per minute.
Here’s the tractor mounted spray-rig again. The farmer ULTIMATELY needs to determine the SPRAY-VOLUME PER HECTARE but a farmer needs to determine the speed of the spray-rig in a particular situation. AREA SPRAYED IS A FUNCTION OF SPEED – KILOMETRES PER HOUR OR METRES PER MINUTE.
The first step is to mark off accurately a convenient distance of say 50 or 100 metres. Use a stopwatch and determine the time it takes for the spray-rig to cover this distance. Do it in both directions as there may be a slope and you need to get an average. If you are spraying a small area with a knapsack just make sure you are walking at a constant speed. Oh, it is not necessary to mark off 50 metres, 30 metres will do. Just make sure you are doing this exercise in the situation you will spraying in.
Practical Example: The spray-rig covers 100 metres in 50 seconds. What’s the speed in kilometres per hour – km/hr. Here’s where it gets interesting. Back in school we had these really lousy teachers who could only explain the method and not the understanding.
Here we have the classic example of SIMPLE PROPORTIONS. “If you cover 100 metres in 50 seconds, how many metres do you cover in 1 minute?” Do you remember this? “Is it going to be more or less? If it is more then divide by less and if it is going to less then divide by more.” This hocus-pocus was enough to confuse the vast majority.
Here’s what you do, just reduce the numbers to metres per second! That pesky word PER. Just read this as FOR EACH. Percent - per centum. FOR EACH 100. So 100 metres per 50 seconds. Or 100m/50sec. Simply put, 100 metres divided by 50sec.
100/50 =2m/sec. For each second the spray-rig covers 2 metres. For each 60 seconds or 1 minute the spray-rig covers 120 metres. There are 60 minutes in an hour so the spray-rig covers 7’200 metres in an hour. 120 metres x 60 minutes=7200 metres per (for each) hour. Almost done!
There 1’000 metres to a kilometre. The spray-rig will cover a distance of 7’200 metres per hour. How many kilometres is that for each hour? 7’200 m / 1000m =7.2 km/hr.
KNAPSACK - STRAIGHT LINE SPRAYING
If you are walking at 1 metre per second what is the speed in kilometres per hour?
chemicon@multispray.com
Tel Intl: +27 83 289 0327
Tel Natl: 083 289 0327
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