Teach lesson
Squeeze the air: what happens to pressure?
Use four readings from a real syringe run to discover what happens to pressure when trapped air has less space.
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Learning Outcomes
Collect four pressure readings from the 20 mL Boyle syringe run.
Describe the direction of pressure change as volume decreases.
Explain the observation using compression and particle collisions.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
The invisible air that pushes back
6 min
When you push the handle of a bicycle pump, the air seems to push back even though you cannot see it. Something similar happens inside a closed syringe: the same amount of air can be trapped in less and less space. What happens to its pressure?
In this activity, *volume* means the space occupied by the air, measured in millilitres (mL). *Pressure* describes the force the gas exerts per unit area on the walls, measured in kilopascals (kPa). You will predict first, then test your idea with four readings from a video of a real experiment.
Before opening the lab, what do you predict will happen to pressure when volume decreases?
Explain your prediction in one or two sentences. You do not need to know Boyle's law yet.
Observe four moments in the compression
10 min
Use the 20 mL syringe, trial 1. The experiment pauses each time the volume decreases. Record only four moments: 20, 16, 12, and 8 mL. Continue through the other pauses without adding rows. If the display uses a decimal comma, enter a decimal point in the table: for example, enter 86,08 as 86.08.
Where to read pressure
Read the large pressure number beside kPa on the LabQuest display; it appears red in the current interface. Read the volume from the current syringe position; each click decreases it by 2 mL.
Lab-screen note: the introduction may mention pressure and temperature. In this Boyle run, syringe volume changes, pressure is measured, and temperature is treated as approximately constant.
Open the Boyle lab
Open the lab with this activity's lab button.
Choose the 20 mL syringe and trial 1.
At 20 mL, read the pressure from the LabQuest display and return here to record it.
Return to the lab and select Decrease by 2 mL. Continue until you reach 8 mL.
Record only the pressures at 20, 16, 12, and 8 mL. Replay a pause if a digit is unclear; do not invent a reading.
Each table row represents one of those four volumes. The volume values are already filled in and locked. Enter one pressure in kPa per row; if the interface shows any extra empty rows, leave them unused.
Four pressure readings
Complete exactly four rows with pressure readings from the LabQuest display.
| Volume mL | Observed pressure kPa |
|---|---|
Turn readings into a pattern
5 min
Now compare the first and last rows, then check whether the readings in the middle rows follow the same pattern.
What pattern do your four readings show as volume decreases?
Write two readings that support your choice using this format: at ___ mL, pressure was ___ kPa; at ___ mL, pressure was ___ kPa.
Explain what we cannot see
4 min
The video shows the result, but air particles are too small to see. When the same air is compressed into less space, particles travel a shorter distance before reaching a wall. Collisions transfer momentum to the walls more frequently per unit area, increasing pressure.
Write three sentences using the particle model above:
1. State the pattern you observed between volume and pressure.
2. Cite two readings from your table, including each volume and pressure.
3. Explain the pattern: the same air occupies less space, so its particles collide with the walls more often.