{SO4.1; SO4.3 Physics of Sound }
SCI – ‘Tin-cup seal hunt’
A TTech-twist on the classic ‘tin-cup telephone’ experiment
Sound waves propagate by the vibration of air between an amplifier (vibrating material) and human ears. Have
you ever listened to sounds recorded underwater? Have you ever tried holding your breath and talking to a friend
underwater? If you have, you know that sound can also propagate through water to our ears.
Inuit hunters used this fact to ‘talk’ to seals and walruses swimming beneath the surface of arctic ice. Marine
mammals are attracted to high-pitched calls and whistles. To make these sounds travel below the water, Inuit
hunters would insert their harpoon tips into a hole in the ice and whistle and hum with their mouth very close to
the shaft. The vibrations caused by their ‘calling’ could travel through the slender harpoon, causing vibrations in
the water under the ice, which traveled to the ears of seals attracting them to the air hole in the ice. Did you
know that sound moves 5 x faster through water than through air?
MATERIALS (per 2 students): 4 plastic cups, nail, bar or soap, ball of string, plastic wrap, elastic bands, salt, sheet of foam or cardboard, >2 foot
wooden doweling or meter stick, plastic tub 1.5 feet deep, water to fill tub
RELATED MEDIA: Short videos by ITEP students demonstrating the propagation of sound waves through different materials: Brittney & Riel –
‘Let’s communicate!’; Barry Linklater – ‘Bottle Xylophone’ and ‘Slinky Sound effects’
Activity part 1: ‘tin-cup telephones’ (10 min)
 Divide students into pairs and have them each take 2 cups
 Use the nail to poke a hole in the centre of each plastic or tin cup
 Have students measure out and cut a piece of string that is about 15 feet long using their rulers
 Wet the bar of soap and have students rub each end of their string on the soap, then roll it between their fingers to make it pointy
 Poke each end of the string through the holes in the cups so that the short ends will be on the inside then tie it to a paper clip to
keep it from slipping back out
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Have students walk apart so that the strings are taught, then hold the cup up to their ear
When one person ‘plucks’ the string, they will both hear a sound emanate from their cup
How tight does the string have to be to get a sound in the cups?
What happens if you pull it tight then talk into the cup – does your partner hear it? Is it louder or softer? Why?
What happens if one end is held against a speaker or other sound source?
How could you ‘mute’ your cup?
Activity part 2: ‘salt dance’ (15 min)
 Give each pair of students 2 new cups
 Stretch plastic wrap tightly over 1 of the cups, like a drumskin, holding it in place with a rubber band
 Set it on a table and sprinkle salt on the cup
 CHALLENGE: without touching or blowing on the salt, table, or cup, make the salt dance
YES: you can use the second cup
YES: you can use your voice
YES: you can use your cellphone
Activity part 3: ‘calling all seals’ (15 min)
 Fill the tub with water
This hands-on activity has been developed by Mohamed Kassem, Masters of Physics and Physical Engineering student and Science Ambassador 2012/2013.. This
document is licensed to the Creative Commons and may be distributed freely with attribution for any and all non-commercial educational purposes
{SO4.1; SO4.3 Physics of Sound }
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tape one cup phone against the wall of the tub with duct tape
have student A take the other end of the cup phone 15 ft away and listen while student B speaks with their mouth just above the
surface of the water – what does student B hear? Switch spots and try again
Now insert the wooden dowling through the surface of the water (not touching the bottom of the tub, and try the process again
with student B speaking or whistling down the shaft of the ‘harpoon’ – is the ‘telephony’ louder or quieter? Higher or lower pitched?
Poke a 1 inch hole in the Styrofoam sheet and place it on the top of the water and try the process again – why is the telephony
louder?
What happens if you ‘make waves’ in the water? What do you hear through the cup phone?
If student B talks into their cup phone, and student A puts their ear in the water, can they hear a message? Is it easier to hear high or low
pitched sounds?
This hands-on activity has been developed by Mohamed Kassem, Masters of Physics and Physical Engineering student and Science Ambassador 2012/2013.. This
document is licensed to the Creative Commons and may be distributed freely with attribution for any and all non-commercial educational purposes