# Fluid Flow Rates

3.0 based on 15 ratings

#### Updated on Feb 04, 2012

Grade Level: 6th - 8th; Type: Physical Science

This experiment will teach students the relationship between fluid flow rate, pressure, and resistance.

• What happens to the flow rate when the diameter of the hole is increased?
• What happens when you increase the pressure within the bottle?

Fluid dynamics is the study how liquids move. Flow rate measures the speed of a liquid. In our homes our sink and shower faucets can be controlled to adjust the flow of water. In our bodies our vascular system controls the flow of blood, also known as blood pressure. Garden hoses are another example where changing the spray nozzle without adjusting the water pressure can change flow of water. In this experiment students will examine how pressure and resistance affect flow rate.

• 3 empty 2L soda bottles
• Awl, knife, pin, or scissors for cutting holes in the bottles
• Water
• Duct tape
• 2000mL graduated cylinder (wide mouth)
• Stopwatch
• Assistant

Perform this experiment outside or in a bathtub.

1. Setup: Place a bottle filled with water on the edge of a table. The bottle will have a small hole where water will flow out. The graduated cylinder on the ground will catch the flowing water so you may have to reposition the cylinder for each trial.

1. Measuring resistance. For each bottle puncture a hole in the bottle using an awl or scissors 3” from the bottom. Make one hole approximately 2cm in diameter, another 1cm in diameter, and finally poke a very small hold using a pin or awl.
2. To fill each bottle, place a piece of duct tape securely over the hole.Fill each bottle with the same amount of water. You can use the graduated cylinder to measure 2L of water.
3. Place the bottle on top of the table with the graduated cylinder positioned so that the flow of water will fall into it. Do an initial trial to position the graduated cylinder by removing the duct tape and allowing water to flow. Once positioned place a piece of tape back on the hole and refill.
4. Start the flow of water by having your assistant remove the tape. As soon as the first drop hits the bottom of the graduated cylinder start your timer.
5. When the water level reaches 1L stop the timer. Record the time.
6. Repeat for each bottle.
7. Measuring pressure. Using the bottle with the 1cm hole repeat steps 3-6 only this time have an assistant apply pressure to the bottle by squeezing gently.
8. What happens to the flow rate when the diameter of the hole increases?
9. What happens to the flow rate when pressure is applied to the bottle?