"If I add more weight to a Hot Wheels car, then it will go faster down the ramp, because heavier things have more energy at the top."
Independent Variable (what I changed): Amount of weight added — 0g, 3.5g, 7g, or 14g of tungsten
Dependent Variable (what I measured): Speed (m/s) and time (seconds)
Controlled Variables: Track length (5.85m), start position, release method, car model (F-150), NFC sticker weight (0.025g)
Base weight: 38.025g
The heavier twin
Base weight: 31.546g
The lighter twin (20.5% lighter!)
| Condition | Total (g) | Trial 1 | Trial 2 | Trial 3 | Avg Time | Avg Speed |
|---|---|---|---|---|---|---|
| No weight | 38.025 | 1.561s | 1.507s | 1.490s | 1.519s | 3.85 m/s |
| +3.5g | 41.525 | 1.481s | 1.481s | 1.515s | 1.492s | 3.92 m/s |
| +7g | 45.025 | 1.504s | 1.478s | 1.499s | 1.493s | 3.92 m/s |
| +14g | 52.025 | 1.515s | 1.508s | 1.483s | 1.502s | 3.90 m/s |
Note: One +14g trial (1.687s) was an outlier (wall hit). Replaced with extra trial.
| Condition | Total (g) | Trial 1 | Trial 2 | Trial 3 | Avg Time | Avg Speed |
|---|---|---|---|---|---|---|
| No weight | 31.546 | 1.544s | 1.510s | 1.477s | 1.510s | 3.88 m/s |
| +3.5g | 35.046 | 1.474s | 1.480s | 1.518s | 1.491s | 3.93 m/s |
| +7g | 38.546 | 1.512s | 1.470s | 1.515s | 1.499s | 3.91 m/s |
| +14g | 45.546 | 1.468s | 1.481s | 1.473s | 1.474s | 3.97 m/s ★ |
| Condition | Car | Mass (kg) | Speed (m/s) | Momentum (kg·m/s) | KE (J) |
|---|---|---|---|---|---|
| No weight | CTL | 0.038 | 3.85 | 0.147 | 0.282 |
| No weight | TST | 0.032 | 3.88 | 0.122 | 0.237 |
| +3.5g | CTL | 0.042 | 3.92 | 0.163 | 0.319 |
| +3.5g | TST | 0.035 | 3.93 | 0.138 | 0.270 |
| +7g | CTL | 0.045 | 3.92 | 0.176 | 0.346 |
| +7g | TST | 0.039 | 3.91 | 0.151 | 0.294 |
| +14g | CTL | 0.052 | 3.90 | 0.197 | 0.374 |
| +14g | TST | 0.046 | 3.97 | 0.181 | 0.359 |
My hypothesis was partly right. Adding a little weight made cars faster (more energy), but adding too much weight made the heavier car slower (more friction). There's an optimal weight for maximum speed — a sweet spot where energy beats friction.
The lighter car had more room before hitting its friction limit, which is why it kept getting faster while the heavier car slowed down.
The M.A.S.S. Trap (Motion Analysis & Speed System) is an ESP32-based physics lab that my dad and I built. It uses infrared break-beam sensors to measure race times to ±0.001 seconds, then calculates speed, momentum, and kinetic energy automatically.