The method and the results are on the waves lab. Do the analysis yourself first, then check the answers below.
Quick answer: A wave is a repeating disturbance that carries energy from place to place without moving matter along with it. These answers go with the grade 7 science lab on waves: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
The sample speeds are close to 2.5 m/s whatever the size of the pulse. Use these model answers to check your analysis, and note that your own spring may give a different speed because the stretch changes it.
Small: (1.62 + 1.58 + 1.66) ÷ 3 = 4.86 ÷ 3 = 1.62 s. Large: (1.60 + 1.64 + 1.60) ÷ 3 = 4.84 ÷ 3 = 1.61 s. Small 1.62 s, large 1.61 s
Question 2 Pulse speeds
Small: v = 4.0 ÷ 1.62 = 2.47 m/s. Large: v = 4.0 ÷ 1.613 = 2.48 m/s. Both about 2.5 m/s
Question 3 Effect of pulse size
The speeds differ by about 0.01 m/s, which is within the timing error, so the size of the pulse (amplitude) does not change the speed. Amplitude does not affect speed. The speed depends on the spring and how tight it is.
Question 4 Frequencies
Slow: f = 14 ÷ 10 = 1.4 Hz. Fast: f = 20 ÷ 10 = 2.0 Hz. 1.4 Hz and 2.0 Hz
Question 5 Predicting wavelengths
Slow: λ = 2.5 ÷ 1.4 = 1.79 m (measured 1.8 m). Fast: λ = 2.5 ÷ 2.0 = 1.25 m (measured 1.2 m). Predicted 1.8 m and 1.25 m, which agree with the measured values.
Question 6 Another prediction
λ = v ÷ f = 2.5 ÷ 2.5 = 1.0 m. The speed stays the same, so a higher frequency gives a shorter wavelength.
Question 7 Timing error
Percentage uncertainty = 0.2 ÷ 1.62 × 100 = 12 %. About 12 %. Film the pulse with a phone and step through the frames, or use a longer distance.
Question 8 Improving the lab
Repeat each run five or more times and take the mean; keep the spring at the same stretch every time; use a longer marked distance; film the pulse for accurate timing. More repeats and better timing.
