6
Evaluate
Testing & Data Collection
Duration
45 minutes
Type
Evaluate
Standards
MS-ETS1-3, 7.RP.A.3
Learning Objectives
Students will be able to:
- Design and conduct a fair test to evaluate CR box performance
- Use PM2.5 sensors to collect quantitative data
- Calculate particle reduction percentage from before/after measurements
- Record data systematically in engineering journals
The Testing Protocol
Step 1: Setup (2 min)
- Place CR box in center of test area
- Position PM2.5 sensor 3 feet from CR box
- Make sure fan is OFF
- Close doors
Step 2: Generate Particles (Teacher Only)
- Burn incense for 2 minutes
- Extinguish and remove from room
- Wait 1 minute for smoke to distribute
Step 3: Baseline Reading (1 min)
- Record PM2.5 reading - this is "Before"
- Wait for stable reading (not fluctuating)
Step 4: Run Test (10 min)
- Turn CR box ON (medium speed)
- Start timer
- Do NOT open doors or move around
- Record PM2.5 every 2 minutes
Step 5: Final Reading
- At 10 minutes, record final PM2.5 - this is "After"
- Turn CR box OFF
- Calculate percent reduction
Understanding PM2.5 Readings
| PM2.5 Level | Air Quality | Color |
|---|---|---|
| 0-12 μg/m³ | Good | Green |
| 12.1-35.4 μg/m³ | Moderate | Yellow |
| 35.5-55.4 μg/m³ | Unhealthy for Sensitive Groups | Orange |
| 55.5-150.4 μg/m³ | Unhealthy | Red |
| 150.5+ μg/m³ | Very Unhealthy | Purple |
Note: Sensors may take 1-2 minutes to stabilize. Wait before recording.
Data Collection Sheet
| Time (min) | PM2.5 (μg/m³) | Notes |
|---|---|---|
| 0 (Before) | Baseline - fan OFF | |
| 2 | ||
| 4 | ||
| 6 | ||
| 8 | ||
| 10 (After) | Final reading |
Calculations
Particle Reduction = Before - After = ____ - ____ = ____ μg/m³
Percent Reduction = (Reduction ÷ Before) × 100 = _____%
Fair Testing Principles
Control Variables
Keep these the same for all tests:
- Room size/location
- Test duration (10 min)
- Starting particle concentration
- Sensor placement (3 ft away)
- Fan speed setting
Variables We're Testing
Independent: Different CR box designs
Dependent: PM2.5 concentration
Example Calculation
A CR box test shows:
- Before: 80 μg/m³
- After: 25 μg/m³
Reduction = 80 - 25 = 55 μg/m³
Percent Reduction = (55 ÷ 80) × 100 = 68.75%
This CR box removed about 69% of particles in 10 minutes!
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| PM2.5 not decreasing | Gaps in seal | Check and repair seams |
| PM2.5 not decreasing | Fan direction wrong | Verify fan exhausts upward |
| Readings inconsistent | Sensor not stable | Wait longer between readings |
| Baseline too low | Not enough particles | Generate more smoke |
| Baseline too high | Previous test lingering | Ventilate room between tests |