The problems are on the sound waves worksheet. Try them on your own first, then compare with the answers below.
Quick answer: Sound is made by vibrations and travels through a medium such as air, water or steel, but not through a vacuum. These worked answers correct the 20 problems of the grade 6 science worksheet on sound waves, from what vibrates? to planning an investigation: each solution shows the formula, the substitution and the final answer with its unit.
Each answer names the idea involved, shows the formula and substitution, and gives the final result with its unit in bold. When you explain, link every statement to vibrations, particles or frequency.
Level: Grade 6 science (Year 7 · Class 6) · Curriculum: MS-PS4-1
Problem 1 What vibrates?
1. The string.2. The drum skin.
3. The vocal cords.
4. The cone of the loudspeaker.
Problem 2 Can sound travel?
Yes through air, water and a steel wall; no through empty space, because a vacuum has no particles to pass on the vibrations.Problem 3 Units of sound
1. The decibel, dB.2. The hertz, Hz.
3. 2 × 1000 = 2000 Hz.
Problem 4 Loudness or pitch?
1. Loudness (bigger vibration).2. Pitch (higher).
3. Pitch (higher, because a shorter string vibrates faster).
Problem 5 Comparing three traces
1. B, because its waves are the tallest.2. C, because it has the most waves in the same time.
3. A and B, which have the same number of waves.
Problem 6 Ear safety
1. Wear ear defenders and take breaks away from the noise (or use a quieter machine).2. Very loud sound can damage the delicate parts of the inner ear and cause permanent hearing loss.
Problem 7 Thunder and lightning
1. d = 340 × 4 = 1360 m.2. 1360 ÷ 1000 = 1.36 km.
Problem 8 Speed in three media
1. Air: 1500 ÷ 340 = 4.4 s. Water: 1500 ÷ 1500 = 1.0 s. Steel: 1500 ÷ 5000 = 0.30 s.2. Steel, because its particles are closest together, so vibrations pass quickly.
Problem 9 An echo
1. 85 × 2 = 170 m.2. t = 170 ÷ 340 = 0.5 s.
Problem 10 Bell in a jar
1. The bell becomes quieter and finally cannot be heard.2. Sound needs particles to pass on the vibrations, and with fewer particles there is less to carry the sound.
3. Space is almost a vacuum, so sound cannot travel; radio waves can.
Problem 11 Frequency
1. 5120 ÷ 20 = 256 Hz.2. 1650 ÷ 3 = 550 Hz.
Problem 12 Ranking pitches
1. Bass drum, man speaking, flute, bat squeak.2. The bat squeak, because 50 000 Hz is above 20 000 Hz.
Problem 13 Noise levels
1. Whisper, conversation and busy road (all below 85 dB).2. Live concert and jet engine.
3. Wear earplugs and stay away from the loudspeakers.
Problem 14 Spot the error
1. Pitch and loudness are different: pitch depends on frequency, loudness on the size of the vibration.2. A quiet whistle has a high pitch but is not loud, and a large drum can be loud with a low pitch.
Problem 15 Hitting a drum
1. A harder hit makes the drum skin vibrate with a larger size, so the sound carries more energy.2. The skin still vibrates at the same number of vibrations each second, so the frequency and pitch stay the same.
Problem 16 Frequency from a trace
1. There are 4 waves.2. 20 ms = 0.020 s.
3. f = 4 ÷ 0.020 = 200 Hz.
4. It would show 8 waves in the same 20 ms (a frequency of 400 Hz).
Problem 17 A moving storm
1. 340 × 7.5 = 2550 m and 340 × 4.5 = 1530 m.2. 2550 − 1530 = 1020 m closer.
3. 1020 ÷ 60 = 17 m/s; 17 × 3.6 = 61.2 km/h.
Problem 18 Sonar on a fishing boat
1. d = 1500 × 0.40 ÷ 2 = 300 m.2. d = 1500 × 0.12 ÷ 2 = 90 m.
3. 300 − 90 = 210 m.
Problem 19 Noise in a factory
1. 95 − 25 = 70 dB.2. It is safe, because 70 dB is below 85 dB.
3. Use quieter machines or sound-absorbing walls, and give workers breaks in a quiet room.
Problem 20 Planning an investigation
1. Change the length of the vibrating rubber band; measure the pitch (frequency), for example with a phone frequency app.2. Keep the same rubber band (thickness and tension) and the same force of plucking.
3. A shorter rubber band gives a higher pitch, because it vibrates faster.
4. Do not stretch a band so far that it can snap towards the eyes; wear safety glasses.
