Grade 2 Science Week 12 | Student Textbook

Grade 2 | SCIENCE

WEEK 12 • STUDENT TEXTBOOK • DAYS 56–60

Read each lesson with a parent or teacher and study the worked example. Then answer the questions for that day in the Week 12 Practice Workbook.

Week 12 Student Textbook | Week 12 Practice Workbook | Week 12 Teacher Guide | Week 11 Student Textbook | Grade 2 index

Day 56: When Wind and Water Move the Land

Erosion can cause problems for people. Rain can wash soil off a farm field, so crops have less soil to grow in. Strong waves can wear away a beach in front of houses. Wind can blow loose soil away from dry fields.

Engineers and farmers design solutions to slow or stop wind and water from changing the land. Before choosing a solution, they ask: What is the problem? What could help? How can we test it?

Worked example: A family’s garden soil washes into the street every time it rains. What is the problem?

Rain is moving the soil.
The soil leaves the garden.

Worked answer: Water erosion is carrying the garden soil away.

Day 57: Plants and Covers Hold Soil

Plants help hold soil in place. Their roots grip the soil like a net, and their leaves soften the falling rain. Farmers plant cover crops, such as grass or clover, so the ground is not left bare.

A layer of straw, leaves or mulch on top of soil also slows the water. The water soaks in instead of rushing away and carrying soil with it.

Worked example: Why do farmers plant grass on a bare slope?

Grass roots hold the soil together.
The grass slows the rain.

Worked answer: So the roots and leaves keep the soil from washing away.

Day 58: Walls, Rocks and Windbreaks

Some solutions are built. A wall or a pile of large rocks along a shore or a riverbank can take the force of the waves so the land behind it is not worn away. A dam can hold back a river and let water out slowly, which helps prevent floods downstream.

Wind can be slowed too. Farmers plant rows of trees and shrubs called windbreaks along the edges of fields. The trees slow the wind, so less soil blows away. Every solution has good points and costs, so people compare them before they choose.

Worked example: A town builds a pile of large rocks along a riverbank. What problem does it solve?

Moving river water wears away the bank.
The rocks take the force of the water.

Worked answer: It slows the river from wearing away the bank.

Day 59: Test and Compare Solutions

Engineers do not guess which solution is best. They build models, test each design the same way, and compare the results.

A good test changes only the design. The hill, the water and the way the water is poured stay the same. Then the results show which design worked better.

Worked example: Why should the hill be rebuilt the same way before testing the second barrier?

If the second hill were steeper, more sand might wash down.
Then we would not know whether the barrier or the hill made the difference.

Worked answer: So the only difference between the two tests is the barrier.

Day 60: Independent Check: Solutions to Erosion

Today you will answer on your own.

Use what you learned this week: erosion problems, plant covers, built solutions, windbreaks, and fair tests that compare solutions.

Worked example: Which slows wind: a windbreak or a dam?

A dam holds back river water.
A windbreak is a row of trees that slows the wind.

Worked answer: A windbreak.