What is a Constant in Science? - Lesson for Kids

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  • 0:03 Constants in Experiments
  • 0:59 Using a Constant
  • 1:58 What Else Can Be a Constant?
  • 2:34 Can You Determine the…
  • 3:34 Lesson Summary
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Lesson Transcript
Corrie Boone

Corrie holds master's in elementary education, taught elementary ESL in the public schools for 5 years, and recently was teaching EFL abroad.

Expert Contributor
Dawn Mills

Dawn has taught chemistry and forensic courses at the college level for 9 years. She has a PhD in Chemistry and is an author of peer reviewed publications in chemistry.

What's a constant in an experiment, and why is it important? Do you need a constant when performing science experiments? Can the constant change? Let's find out!

Constants in Experiments

Have you ever done a science experiment? Maybe you've done one at school in science class, for a science fair, or just for fun? Experiments are fun because they teach you a lot about how the world around you works. When doing science experiments, there are different parts of the experiment that must be included for the results to be accurate and valid.

Science experiments usually include an independent variable, dependent variable, and control. Remember, an independent variable is the part of the experiment the scientist changes or controls. The dependent variable is the part of the experiment that reacts to the independent variable. The control is the base experiment for comparison with other trials of the experiment. Science experiments also include something called constants. A constant is the part that doesn't change during the experiment.

Using a Constant

Let's apply these parts in an example experiment. Say we want to know how long it takes an ice cube to melt. You can easily perform this experiment by putting an ice cube in a bowl on your kitchen counter and timing how long it takes to melt. This base experiment (the ice cube melting at room temperature) becomes your control, and different outcomes will be compared to this control.

Now say we want to see how long it takes an ice cube to melt at different temperatures. This time, we put one ice cube outside in the sun and one in the fridge. Changing the temperature will affect how long the ice takes to melt. Since the temperature changes, temperature is the independent variable.

The amount of time it takes the ice cube to melt is the dependent variable, because this will change based on the independent variable. The constant in this experiment is the ice cube: it is the same size - at least at first - in each trial of the experiment.

What Else Can Be a Constant?

A constant must stay the same throughout the experiment. However, the constant can be many different aspects of the experiment.

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Additional Activities

Determining the constant in a science experiment

In this activity, an experiment will be preformed using constant and changing variables to determine how the changes affect the results of a controlled setting.


3 small planters dishes

Potting soil

Plant seeds



Baking soda

3 Tupperware or closed containers

Experimental procedures

1. Label the planter dishes 1 to 3.

2. Fill the planter dishes half way with potting soil.

3. Place a few seeds in the soil in each pot.

4. Cover the seed with another 1-2 inches (2.5 - 5 cm) of potting soil.

5. Place the pots in an area with access to sunlight.

6. Add tap water into the closed containers. Label one of the containers "1".

7. Add a tablespoon of vinegar to one of the containers and label as "2".

8. Dissolve 2 tsp of baking soda to the final container and label "3".

9. Each day, water each pot with its corresponding solution. (Example: Pot 1 will be watered with solution 1).

10. Record your observations over the next week or two, or until the plants have all spouted. (Can continue longer with the experiment as desired)


1. Did the use of an acid (vinegar) or base (baking soda) affect the plants ability to grow?

2. Which plant was the largest?

3. What was the constant in this experiment?

4. Can you think of additional factors to test that may affect the growth of a plant? Be sure to note what would be constant or used as the "control" to compare against.


The acidic solution should affect the health of the plant. For example, yellowing leaves or stunted growth could be expected. The basic solution may not affect the growth or health of the plant as compared to the control. However, prolonged exposure to the basic solution could decrease the health of the plant over longer periods of time. The constant in this experiment is using regular water for the plants. There are other factors that could be tested to affect the growth of the plant. For example, a plant could be kept out of the sun and another placed in the dark and compared.

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