Thread Telephone — Sound through Solids (Class 8, ICSE)
Simple cup-and-thread experiment to show sound travels through solids
Materials
- 2 disposable paper/plastic cups
- 2–3 m of thread (cotton, wool, or metal wire for comparison)
- Sharp pin or pencil to make holes
- Paper clip or matchstick to hold the thread inside cup
- Scissors and a partner
Procedure (Short)
- Make a small hole in the centre of each cup base. Pass the thread and secure it with a clip.
- Two students stand apart and stretch the thread tightly between cups.
- One student speaks softly into one cup while the other listens from the other cup.
- Observe how the sound changes when thread is loose, touches an obstacle or made of different material.
Key Observations
- Sound travels as vibrations through the thread (solid).
- Tight thread and rigid materials (metal) give clearer sound.
- Loose thread, soft yarns or wet thread reduce clarity.
Question & Answer Session — (Use after the activity)
1. What is used in this experiment?
Answer: Two cups connected by a thread (cup telephone).
2. What happens when one student speaks into one cup?
Answer: Vibrations travel through the thread and the sound is heard in the other cup.
3. What happens if the thread is loose?
Answer: The sound becomes weak or unclear.
4. Why should the thread be tight?
Answer: A tight thread transmits vibrations more effectively.
5. What happens if the thread touches a wall?
Answer: Vibrations get disturbed and the sound becomes unclear.
6. What happens if thread is replaced by metal wire?
Answer: Sound will be clearer because metal conducts vibrations well.
7. If two threads cross at the centre and two pairs speak simultaneously, will they hear each other clearly?
Answer: No — sounds may mix or interfere and become unclear.
8. Which material gives the faintest sound?
Answer: Soft wool yarn (it absorbs vibrations).
9. What happens if the thread is wet?
Answer: Sound becomes weaker as water dampens vibrations.
10. Write one conclusion from the experiment.
Answer: Sound can travel through solids and needs a medium to travel.