Do Thick Liquids Flow Faster or Slower Than Thin Ones?

Talk It Over

Liquids flow or run over surfaces—you notice that when you spill them. Do some liquids flow faster or farther than others? Does how thick or thin they are make a difference?

Get

• Piece of glass (glass from a large picture frame works well)
• Glass cleaner and dry cloth
• Ruler
• Books
• Liquids for testing, such as molasses, vegetable oil, vinegar, and water
• Droppers (a clean dropper for each liquid)
• Stopwatch or clock with a second hand

Go

1. Clean the glass with the glass cleaner and cloth.
2. Measure the length of the glass plate with the ruler. This is the distance your liquids will travel. Record this number.



3. Set one or more books on your work surface. Set an end of the glass on the books, like this:



4. Pull a little of the liquid you want to test into a clean dropper.
5. Quickly drop 5 drops of the liquid onto the glass plate at its high point. Immediately start the stopwatch (or note the time on the clock with a second hand).



6. When the stream of liquid reaches the bottom of the glass, stop the stopwatch (or note the elapsed time). Record how long the liquid took to reach the bottom of the glass.
7. Clean the glass and repeat steps 3–6 twice more with the same liquid.
8. Calculate and record the average travel time for this liquid:



9. Clean the glass and repeat steps 3–8 with each of the liquids you wish to test.

Stay Safe

Careful with the glass plate. Its edges may be sharp.

Go Easy

Use the "Go" procedure to compare only two liquids, a thick liquid like maple syrup and a thin liquid like water. Get an adult's help with measuring, timing, and averaging.

Go Far

Viscosity is the resistance of a liquid to flow. Thick liquids have high viscosity. Thin liquids have low viscosity. Use the "Go" procedure to compare the viscosity of several liquids. Calculate and compare the rate of travel for the liquids in centimeters per second using this formula:

distance traveled (length of glass in centimeters) ÷ time of travel in seconds = cm/sec

You might also try comparing the viscosity of different brands of maple syrup or different weights of motor oil.

Show Your Results

Put travel times in a data table like this for "Go Easy":

For "Go," use the same data table, adding a row for each liquid you test. Make a bar graph that compares travel times.

For "Go Far," make a bar graph that compares your calculated values of distance traveled per second. Make graphs to show the results of any other experiment you conduct.

Tips and Tricks

• Make sure you clean and dry the glass thoroughly between each trial. Dirty glass will affect your results.
• If 5 drops are too much (the liquid travels too fast) or too little (the liquid travels too slowly), decrease or increase the amount. Just make sure you use the same amount in all tests of all liquids or your comparisons will not be valid.
• If your liquids are traveling too slowly or quickly, try using more or fewer books to raise or lower the starting point.

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