Flow Force Teacher Guide Flow Force
Teacher Facilitation Guide
Earth Science / Geography
Grades 6-8
Lesson Objective
Students will model how stream gradient impacts erosion velocity. By the end of this lesson, students will be able to explain the relationship between potential energy, kinetic energy, and the physical carving of landscapes by rivers.
Time Estimate
50 Minutes
Key Terms
• Stream Gradient
• Erosion Velocity
• Potential Energy
• Kinetic Energy
Required Materials
Stream Table Trays (deep plastic bins)
Sand (fine play sand works best)
Water Pitchers (constant flow)
Protractors (to measure tray angle)
Stopwatches (digital or phone)
Gradient Gamble Worksheets
Instructional Sequence
05
Warm-up: The Smoke That Thunders
Visual Hook & Discussion
"How did water cut through that rock? Why does it fall so violently here but look tame just upriver?"
Show video clip (0:00-0:30). Have students turn and talk to a neighbor before sharing ideas with the class.
10
Concept Deep Dive: Stream Energy
Video Viewing & Guided Notes
Watch the "Stream Energy & Gradient" section (4:43-5:38). Pause to discuss:
Potential Energy: Energy stored due to elevation.Kinetic Energy: Energy of motion as water flows downhill.Gradient: The "steepness" of the slope.
25
Modeling Activity: Stream Tables
Hands-on Investigation
Students will work in groups of 4 to test three different gradients (10°, 20°, and 30°). They will measure how long it takes for a pulse of water to travel the length of the tray and sketch the resulting "canyons."
Teacher Tip: Ensure students pour water at a consistent rate. Using a pitcher with a small spout or a cup with a hole in the bottom helps control the flow.
05
Closure: Connecting to the Zambezi
Synthesis & Exit Ticket
Compare class results with the video's explanation of the Upper vs. Middle course of the Zambezi. Ask: "Which course of the river did your steepest gradient tray best represent?"
Assessment
Review student observations and canyon sketches on the Gradient Gamble Worksheet for accuracy in representing high-velocity erosion.
Differentiation
Provide pre-measured "hill" blocks for students who struggle with using protractors. Challenge advanced students to calculate actual velocity (cm/s).
Stream Scrapers Slides Stream Scrapers
MODERN RIVER GEOGRAPHY & EROSION
Gravity • Gradient • Power
Mosi-oa-Tunya
The Smoke That Thunders
Warm-Up
Embedded media
"How did water cut through that solid rock?"
Observe
Watch the scale of the falling water. Notice the spray and the noise described as 'thunder'.
Discuss
Where does the power come from? Is the water moving faster here or further upriver?
Flow Mechanics
Gravity
The engine that pulls water from high to low elevation.
Potential
Energy stored because of height above sea level.
Kinetic
Energy in motion as the water rushes downhill.
Higher elevation = More potential energy = Faster kinetic flow
Gradient Power
Deep Dive
Embedded media
Definition: Gradient
The change in elevation over a specific distance.
Steeper Gradient = Higher Energy
Think About It
If the riverbed is flatter, what happens to the energy available for erosion?
Lab Mission
Your Goal
Model how the angle of the riverbed (gradient) changes the speed of the water and the amount of sand moved.
Test 1
10°
Test 2
20°
Test 3
30°
Safety & Setup
Pour water slowly and at a constant rate.
Keep all water inside the tray area!
Use the protractor to check your angle carefully.
Sketch the resulting canyon on your worksheet.
Real-World Results
Upper Course
Peat swamps, very low gradient.
Result: Slow water, very little erosion power.
Middle Course
Gradient steepens dramatically.
Result: High energy, massive erosion (Victoria Falls & Gorges).
Final Discussion
Which of your lab tests (10°, 20°, or 30°) looked most like the Middle Course of the Zambezi?
Gradient Gamble Worksheet Gradient Gamble
Hydrology & Erosion Lab
Name:
Date:
Research Question
How does the steepness (gradient) of a stream bed affect the velocity of water and the amount of sediment eroded?
Lab Hypothesis
If the gradient (angle) of the tray is increased, then the velocity of the water will...
Data Collection
Test Angle Time to Reach Bottom (s) Erosion Observation 10° (Low Gradient) 20° (Moderate Gradient) 30° (High Gradient)
Energy Check
Potential Energy was HIGHEST at:
10°
20°
30°
Kinetic Energy was HIGHEST at:
10°
20°
30°
Erosion Field Sketches
Sketch the shape of the 'river channel' or canyon left behind in the sand after each pour.
10° Gradient
20° Gradient
30° Gradient
Analysis & Case Study
1. Compare the width and depth of the 10° canyon vs. the 30° canyon. Which one had more power to "move rock and sediment"?
Zambezi Connection
2. The video explains that Victoria Falls formed in the Middle Course because the gradient steepened. Which of your lab tests (10°, 20°, or 30°) most closely modeled the Middle Course? Explain why.
3. If you were a city planner in Africa, would it be safer to build a bridge over the river during its Upper Course (low gradient) or Middle Course (high gradient)? Why?
End of Field Notes
Gradient Gamble Answer Key Gradient Gamble
Teacher Answer Key
Flow Force Lesson
Lab Hypothesis
"If the gradient (angle) of the tray is increased, then the velocity of the water will increase and the amount of sediment moved will increase."
Sample Data (Results may vary)
Test Angle Time to Reach Bottom (s) Erosion Observation 10° (Low) ~5.5 sec Slow, clear water. Only a tiny shallow path in the sand. 20° (Moderate) ~3.2 sec Noticeable sand movement. A definite channel is formed. 30° (High) ~1.8 sec Rapid water flow. Deep, wide canyon cut quickly into the sand.
Potential Energy was HIGHEST at:
30° Gradient
Kinetic Energy was HIGHEST at:
30° Gradient
Analysis Key
Question 1: Canyon Comparison
The 30° canyon should be significantly wider and deeper. Because the gradient was steeper, gravity converted more potential energy into kinetic energy (velocity). Faster water has more force to lift and transport sand grains (erosion power).
Question 2: Zambezi Connection
The 30° test models the Middle Course. In the Middle Course, the gradient increases, giving the river more energy to carve out features like Victoria Falls and the basalt gorges.
Question 3: City Planning
It is generally safer to build over the Upper Course (in this specific case study). The water is slower and has less erosional force to wash away bridge foundations. In the Middle Course, the high energy and turbulent flow make construction much more dangerous and difficult.
Grading Tip
Look for students using scientific vocabulary (potential, kinetic, gradient) in their explanations. Ensure their sketches accurately reflect the data recorded (e.g., deeper canyons for steeper angles).
Stream Lab Setup Guide Stream Lab Prep
Physical Setup & Safety Guide
Station Layout
Each group of 3-4 students needs a clear, flat surface (lab table or desk). Protect surfaces with plastic tablecloths if necessary.
Each Station Needs:
1 Stream Tray (approx. 24" x 12")
5 lbs of fine-grained sand
1 Pitcher of water (500mL)
1 Protractor
1 Large bucket (to catch runoff)
Blocks or books (to prop tray)
Tray Preparation
1 Fill the top 2/3 of the tray with sand. Pack it down firmly to create a smooth, flat "land" surface.
2 Position the tray so the bottom end hangs slightly over a bucket to catch the water and sediment.
3 Instruct students to smooth the sand back to "flat" between each test (10°, 20°, 30°).
Control Your Variables
Consistent Flow
Students must pour at the same speed every time. Use a funnel or a cup with a small hole to keep flow constant.
The Start Line
Always pour from the exact same spot at the top of the tray.
Water Volume
Use the same amount of water (e.g., 200mL) for every test.
Troubleshooting
Sand is moving too fast?
Wet the sand slightly before starting to increase "cohesion." This mimics real soil and makes the erosion patterns more visible.
Water is pooling?
Check that the drain end of the tray isn't blocked by a large "sand bar." Help students dig a small exit channel if needed.
Lab Safety: Clean up spills immediately to prevent slipping.
Material ID: flow-force-prep
