What happens when it not only rains but it pours. 

26 03 2017

My brother lives on a farm in central NSW. Tuesday morning they had over 100 mm of rain in the order of 4 hours. Wednesday afternoon there was a further 63 mm in half an hour and Thursday afternoon it started raining heavily about 5. By about half an hour later there’d been just under another 50 mm.

Some of the water from the local to distant area runs past their house and into a creek.

When the last fall of rain came the water running past the house was about 20 m across and 400 mm deep and running at about 40m/min. My brother watched a moving leaf to get the rate of flow. As the runoff from the rain increased, the depth of the water increased to about 700 mm.

If calculations are made on 40 m/min X 20 m X 400 mm, you get 320 cubic metres per minute which is 19200 cubic metres per hour which is 19200000 litres per hour or 19.2 megalitres per hour.

It has been running at least this deep for the last 48 hours which calculates to be 921.6 megalitres or 921600 cubic metres of water.

At the times where the depth raised to 700 mm the rate of flow would have been faster- it was dark so we can only estimate that it was possibly at least half as fast again. This calculates to 50.4 megalitres per hour or 50400 cubic metres of water per hour.

That 3 day rainfall is half the average annual rainfall.

All in the day of being a farmer!


Grandpa Helpful

20 06 2013

The Review Task for Year 9 this week gave them a packing problem. The scenario was that their grandfather was moving into a retirement village and needed to work out the cheapest way to move his furniture, in a single trip.

They were given the dimensions of the furniture in inches and the dimensions of the transport vehicles in centimetres. They were told to spend a maximum of 30 minutes on their solution.

Grandpa Helpful 1Most students were able to draw a conclusion in the allocated time. Interestingly one student calculated the volume of the items and that of the delivery vehicles and made their decision based on these calculations.

Surface Area with a Difference

1 06 2013

Recently my pre-service teacher wanted a practical lesson for surface area incorporating technology. She came up with 2 scenarios using Google Sketchup.
Scenario 1
a). Using Sketchup, draw a house that consists of a rectangular prism base and pyramid roof.
The dimensions of the base of the prism need to have a total perimeter of 20 m.
b). Draw a door on one of the sides of the house that has an area of 3 square metres
c). Draw 2 windows on 2 different sides which both have an area of 2 square metres
d). Using the “dimensions” tool, place the labels for all critical dimensions onto the house. Copy the screen and save in a Word file.
e). Calculate the surface area of the outside walls and roof of the house.
f). Calculate the inside volume of the house (assume no wall width and no internal walls or ceiling)

We then wanted a component of the lesson which was a little more relevant to the girls in the class.
Scenario 2
Mary wants to make a birthday cake for her friend Tom. She wants to bake a 3 layer cake for his birthday.
a) Using Sketchup, draw a cake that consists of 3 layers of rectangular prisms. Each layer must be 10cm shorter in length than the layer below
b) Using the “dimensions” tool, place the labels for all critical dimenions onto the cake. Copy the screen and save in a Word file.
c) Calculate the surface area of the cake to be covered with icing (assume that only the visible faces of the cake will be iced)
d) Mary has discovered rectangle cake decorations that have a surface area of 8 square centimetres. Calculate how many decorations will be needed to completely cover the visible surface of the cake.

The students were fully engaged by the lesson. As they left the class they were each given a muffin with a fondant lego brick as decoration on top.

Slurpee for $2.90

8 09 2012

My classes were all talking about 7-eleven’s Slurpees on Wednesday. Once we knew the diameter could be up to 23cm and the depth 28 cm I set them to calculating the capacity of a cylinder compared to a square prism. It made for a practical interlude to the lesson in both Year 11 and Year 9.