❓ What makes a good science fair question

One thing changed, one thing measured

Every good question has two parts hiding in it: the thing you change on purpose, and the thing you measure to see what happened. Everything else stays the same, so you know your change caused the difference.

Try saying your question in this shape: if I change ___, what happens to ___? If you can fill both blanks, and the second blank is something you can count, time or measure with a ruler, you have a test.

A good question also has an answer you don't know yet. If you're sure what will happen, it's a show, not a test.

Ten good questions

Each of these is a real project here, with its steps and its sheets. Look at how each one changes one thing and measures one thing:

• Does a steeper ramp make a toy car go farther? You change how high the ramp is and measure how far the car rolls.
• Does a longer arm make a catapult throw farther? You change how long the catapult's throwing arm is and measure how far the paper ball flies.
• Which cup keeps an ice cube from melting longest? You change what the cup is made of and measure how long the ice cube takes to melt all the way.
• Does planting a seed deeper make it slower to come up? You change how deep the bean is planted and measure how many days until the shoot pokes out of the soil.
• Does crumpled paper fall faster than flat paper? You change the shape of the paper and measure how long the paper takes to fall.
• Does ice melt faster in water or in air? You change where the ice cube sits and measure how long the ice cube takes to melt.
• Does more vinegar blow a balloon up bigger? You change how much vinegar goes in the bottle and measure how far around the balloon is.
• Does a bean grow taller in the dark? You change how much light the bean plant gets and measure how tall the plant grows in ten days.
• Does a shadow grow when the light comes closer? You change how far the flashlight is from the toy and measure how long the toy's shadow is on the wall.
• Which soaks up the most: a sponge, a paper towel or a cloth? You change what soaks it up and measure how many spoonfuls it holds before it drips.

Ten weak questions, and why they fail

These are written to fail, so you can spot the problem. Each one is missing something a test needs.

• "Which paper airplane is the coolest?" Cool is an opinion, and a ruler can't measure it. Measure how far each one flies instead.
• "Is my toy car fast?" Fast compared with what? A test needs at least three levels of the thing you change.
• "What happens when you mix baking soda and vinegar?" It fizzes, every time. That's a show, not a test. Change how much baking soda goes in and measure the foam.
• "Do plants need light?" Everybody knows the answer already. Ask how far a plant leans toward the window instead.
• "Does a ball bounce higher on carpet if I throw it harder and use a different ball?" Three things changed at once, so you can't tell which one made the difference.
• "What are clouds made of?" That's a question for a book. Nothing gets changed and nothing gets measured.
• "Does an ice cube melt faster in the sun with salt on it?" Two changes again: the sun and the salt. Change one at a time.
• "Why is the sky blue?" A great question, but you can't change the sky. Pick something you can change with your own hands.
• "Which paper towel is the best?" Best at what? Say what you'll measure: how many spoonfuls of water each one holds.
• "Does sugar dissolve in water?" Yes, and that's the end of it. Ask how fast it dissolves at three different temperatures.

Turn a weak question into a good one

Most weak questions have a good one inside them. Ask yourself three things:

• What will I change? Pick one thing, and three amounts or kinds of it.
• What will I measure? Something with a number: centimetres, seconds, pennies, spoonfuls.
• What will I keep the same? At least two things, so the test is fair.

Then write it on the hypothesis sheet, or let Pick my project hand you a question that already works. Want to practise spotting the weak ones? Try the quizzes.