Good Science Victorian Curriculum Year 7

INVESTIGATIONS
Investigation 7.2
Investigating soil erosion
KEY SKILL
IDENTIFYING THE VARIABLES AND
FORMULATING A HYPOTHESIS
Before you formulate a hypothesis, identify your
independent, dependent and controlled variables.
The independent variable is the one thing that you
purposefully want to change in an investigation.
The dependent variable is what you will be measuring.
The controlled variables are all the things you need
to keep the same throughout the investigation.
To formulate your hypothesis use the following sentence
stem: It can be hypothesised that if (something to do with
your independent variable), then (something to do with
your dependent variable).
Hint #1: If you get stuck, use the prompts in Lesson 1.4
to help you.
AIM
To investigate factors that influence soil erosion
MATERIALS
• several small seedlings
• soil
• small amount of mulch
• 6 empty soft-drink bottles (equal shape and size)
• piece of board or bench space (30 cm × 30 cm)
• glue or plasticine
• string
• 250 mL beaker
• water
METHOD
1 Cut a rectangle (approximately 10 cm × 20 cm) out of
one side of three of the bottles.
2 Using glue or plasticine, position the bottles on their
sides (holes facing up) on a table or board so that
they will not move. The necks of the bottles should
stick out over the edge.
60 min
Level 1
3 Add an equal amount of soil to each of the three
bottles.
4 Plant your seedlings in the first bottle.
5 Cover the soil in the second bottle with a layer
of mulch.
6 Leave the soil uncovered in the third bottle.
7 Cut the other three bottles in half and carefully
pierce a hole on either side to thread the string
through so that it can be suspended underneath
the necks of the three bottles.
8 Use the beaker to measure 250 mL of water and
carefully pour the water into each bottle containing
soil, pouring into the bottom of the bottle, away from
the neck.
9 When the water has drained through, record your
observations of the differences in the water that
collects in the buckets underneath the neck.
10 Repeat the watering process over several days,
continuing to record your observations.
QUESTIONS
1 Compare the colour of the water in each of the
collecting cups.
2 Describe the level of soil remaining in each of the
three bottles.
3 Suggest why the colours and levels of soil are
different.
4 Farmers will often leave the roots of their old crop
in the ground until they are ready to plant their
new one. Justify why this is a useful strategy for
preserving soil resources.
5 A farmer observed that soil will erode more from
paddocks that are on a slope than in paddocks on flat
ground. Design an experiment to test how the angle
of a slope affects the amount of soil eroded.
CONCLUSION
Copy and complete:
‘The results show that: (respond to the aim)’.
170 GOOD SCIENCE VICTORIAN CURRICULUM 7