Understanding Variables in Experiments

What is an independent variable?

• What a scientist changes in an experiment to test their hypothesis

• What scientist measure to see if it responded to a change

• What happens when you do an experiment

• What you keep the same throughout all experimental groups

Answer explanation

The independent variable is what a scientist changes in an experiment to test their hypothesis. This choice is correct because it directly relates to the manipulation that drives the experiment's outcome.

What is an dependent variable?

• What a scientist changes in an experiment to test their hypothesis

• What scientist measure to see if it responded to a change

• What happens when you do an experiment

• What you keep the same throughout all experimental groups

Answer explanation

The dependent variable is what scientists measure to see if it responded to a change in the experiment. This choice correctly identifies the role of the dependent variable in testing hypotheses.

While studying how physical activity influences the human body, a student decides to measure heart rate at different levels of exercise. The student checks their pulse after resting, walking, and running for five minutes, predicting that more intense activities will lead to higher heart rates. What are the independent and dependent variables?

• IV: Length of time spent exercising; DV: Type of exercise

• IV: Type of exercise; DV: Heart rate

• IV: Heart rate; DV: Time spent exercising

• IV: Time spent exercising; DV: Heart rate

Answer explanation

The independent variable (IV) is the type of exercise (resting, walking, running), as it is what the student changes. The dependent variable (DV) is the heart rate, as it is what is measured in response to the exercise type.

To explore chemical reactions, a student adds varying amounts of baking soda to the same amount of vinegar each time. The aim is to see how the amount of baking soda affects the size of bubbles produced during the reaction. The student believes more baking soda will result in larger bubbles. Which is the independent variable, and which is the dependent variable?

• IV: Size of bubbles; DV: Amount of baking soda

• IV: Amount of baking soda; DV: Size of bubbles

• IV: Amount of vinegar; DV: Size of bubbles

• IV: Size of bubbles; DV: Amount of vinegar

Answer explanation

The independent variable (IV) is the amount of baking soda, as it is what the student changes. The dependent variable (DV) is the size of bubbles, as it is what is measured in response to the changes in baking soda.

A student investigates the effect of different light colors on plant growth. They use red, blue, and green lights to grow three sets of identical plants and measure their height after two weeks. The student hypothesizes that plants under blue light will grow the tallest. What are the independent and dependent variables?

• IV: Type of plant; DV: Color of light

• IV: Height of plant; DV: Type of plant

• IV: Color of light; DV: Height of plant

• IV: Height of plant; DV: Color of light

Answer explanation

The independent variable (IV) is the color of light, as it is what the student changes to observe its effect. The dependent variable (DV) is the height of the plant, as it is what is measured in response to the light color.

In a physics experiment, a student drops different weights from the same height to measure the time it takes for each weight to hit the ground. The student predicts that heavier weights will fall faster. What are the independent and dependent variables?

• IV: Height of drop; DV: Weight of object

• IV: Weight of object; DV: Time to hit the ground

• IV: Time to hit the ground; DV: Weight of object

• IV: Weight of object; DV: Height of drop

Answer explanation

The independent variable (IV) is the weight of the object, as it is what the student is changing to see its effect. The dependent variable (DV) is the time to hit the ground, as it is what is being measured in response to the weight.

A student is testing the effect of different concentrations of salt in water on the boiling point. They prepare solutions with varying salt concentrations and measure the temperature at which each solution boils. The student expects that higher salt concentrations will increase the boiling point. What are the independent and dependent variables?

• IV: Boiling point; DV: Salt concentration

• IV: Temperature; DV: Salt concentration

• IV: Salt concentration; DV: Boiling point

• IV: Boiling point; DV: Temperature

Answer explanation

The independent variable (IV) is the factor that is changed, which is the salt concentration. The dependent variable (DV) is what is measured, which is the boiling point. Thus, IV: Salt concentration; DV: Boiling point.