Energy sums, pressure, waves and circuits

The diver you control with a squeeze

How does squeezing a sealed bottle make an object inside sink and rise?

25 minAt home

Watch first

An English teaching video on this topic from Massimo Boscherini. Watch it, then scroll down for the lesson.

What you need

Tick each one as you find it — 0 of 4 ready.

A clear plastic bottle with a screw cap, filled to the top with water
A drinking straw, paperclip and a little blu-tack (or a ketchup sachet)
Scissors
A jug of water

Plan the fair test

Change: How hard you squeeze the bottle
Measure: Whether the diver floats, sinks or hovers
Keep the same: The same diver, the same bottle filled to the brim, the same water temperature

Objectives this evidences

Understand pressure in fluids and atmospheric pressure, and pressure on surfaces

Do it, one step at a time

Step 1 of 4

Step 1. Cut a 4 cm piece of straw, seal one end with blu-tack and weight the open end with the paperclip so it just barely floats upright in the jug. Adjust the blu-tack until it floats with only the top showing.
Step 2. Drop your diver into the bottle, fill the bottle completely to the brim and screw the cap on tight.
Step 3. Squeeze the sides of the bottle gently and watch the diver. Squeeze harder, then release. Record what happens at each pressure.
Step 4. Push the bottle under water, squeeze and watch the water level inside the straw. Draw a labelled diagram of the air bubble at the surface and at the bottom.

What should happen

Squeezing raises the pressure everywhere in the water, which squashes the air bubble in the straw, lets water in, and the diver sinks. Releasing lets it rise.

Think about: Why must the bottle be completely full and sealed? What does that tell you about how pressure passes through a fluid?

Write up your result

What did you measure, and what pattern did you see?

A sentence or two is enough to save it.

The lessons behind this practical

Each one opens with the same short film, and the film has a written transcript underneath if reading is easier than watching.

Energy you can count: calculating and conserving it Pressure on surfaces, in fluids and in the atmosphere Light waves and sound waves compared Current, voltage, series and parallel

Now the quiz for this topic

Questions come from the lessons behind this practical, so nothing is asked that has not been taught.

Quiz

Energy sums, pressure, waves and circuits quiz

8 questions from the lessons in this stage. No timer, and you can try again as many times as you like.

All experiments Year 8 science pathway