Which of these could send a message using sound?

• A mirror
• A string telephone
• A torch

Which of these could send a message using light?

• A flashing torch
• A string telephone
• A drum

A loose, floppy string works as well as a tight string in a cup telephone.

Why can two friends use torch flashes to send an agreed message at night?

• A torch makes its own light.
• A torch needs sunlight to make a message.
• A torch carries the message using sound.

You speak into a cup telephone with a tight string. How does your message reach the other cup?

• The string changes spoken words into flashes of light.
• The words travel only through air; the string does nothing.
• Vibrations travel through the cups and string.

A torch flashes twice, pauses, then flashes twice more. How many flashes are in the whole signal?

Ben uses a flash pattern for 'come here'. Asha thinks it means 'stay there'. What should they do before testing again?

• Repeat the pattern with a brighter torch without discussing it.
• Change to a longer string without discussing the flash pattern.
• Agree on one meaning for that flash pattern.

Mia wants to find out whether tight string helps her cup telephone. Which test lets her compare string tightness?

• Use new cups and new messages whenever string tightness changes.
• Use the same cups and message; change only string tightness.
• Change the distance and voice whenever string tightness changes.