Bernoulli’s Mist Sprayer

No doubt students learn more when they are mentally and physically engaged in the learning process, regardless of the subject they are studying, and when it comes to STEM education, hands-on experiential learning is an indispensable part of the learning process.

In this hands-on activity, we will make a water sprayer using two straws, and experience Bernoulli’s Theorem.

Category: Physics

Sub Topic: Fluid Pressure

Time Required: 20-30 min

Difficulty: Easy

• 2 Straws (4 inches each)
• Insulation Tape
• Eraser
• Scissors
• A glass of water
• Student observation sheet (attached)

• Pic 1: Cut two insulation tape pieces and attach them to either end of both the straws.
• Pic 2: While attaching the tape, make sure to leave some space from the end(4-5mm approx).
• Pic 3: Tape the 1st straw(I used Green straw as 1st) to the eraser so that the straw is exactly aligned with the edge of the eraser.
• Pic 4: Next, tape the second straw(I used Orange straw as 2nd) to the edge of the eraser so that it blocks half of the opening of the 1st straw.

To use this mist sprayer, insert 2nd straw into a glass of water and blow air forcefully through 1st straw. Observe a perfect misty spray coming out from the junction of the two straws.

Troubleshooting:
Here is a checklist in case the sprayer doesn't work:

• Make sure that you are blowing air from 1st straw and not the 2nd straw.
• You are blowing air forcefully and not gently.
• The insulation tape is not compressing the straws.

Variations:

Encourage students to think of different variations and note down their observations. Students can experiment by varying the length or diameter of the straw or experiment by dissolving sugar in water and vary its density.

According to Bernoulli’s Theorem, the pressure is inversely proportional to the square of the velocity. In other words, the faster a fluid(gas or liquid) moves, the lower the pressure.

In this activity, we have attached two straws in such a way that one straw is partially blocking the opening of the other straw. This blocking results in creating a nozzle-like effect at the blocked end of the straw. Now, when we blow air through the partially blocked straw this nozzle increases the speed of the air and the air comes out at a much faster velocity, thereby reducing the air pressure at the junction of the two straws. This difference in pressure at the end of the second straw results in sucking up of water from the glass.

This combined role of two straws results in a perfect misty spray coming out from the junction of the two straws using Bernoulli’s Theorem.