Science · Grade 3 Science
Chapter 1: Forces and Motion
Change one thing. Write down what you kept the same.
Watch first. The explanation comes later.
Two runs of the same experiment. In the second one somebody increased the pull and also swapped the surface. The block went further.
Was that the pull or the surface? Can anybody tell?
Deliberately change both the pull and the surface, and see what you can conclude.
Step 1 — Predict
You change the pull AND the surface, and the block goes further. What caused it?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Keep the surface on wood the whole time. Change only the pull.
Step 1 — Predict
Same surface, bigger pull. What will happen to the distances in the table?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Now the explanation, after you have seen it happen.
A variable is anything in an experiment that could be different from one run to the next: the slope, the surface, the weight, the size of the push, even how warm the room is. Naming them all is the first job, because you cannot control something you have not noticed.
Variable Something in an experiment that could be changed.
Change one variable and hold every other one still. Then any difference must be caused by the one you changed.
If you change two things and something happens, you cannot say which one did it. The run is wasted.
That list is as important as the thing you changed. Without it nobody can repeat your test.
To test whether the surface matters, use the same trolley, the same slope, the same push, and change only the surface. Listing what you held constant is as much a part of the method as what you changed.
Do each run three times and compare. If the three are close, the result is reliable. If they are wildly different, something you were not controlling is affecting it.
Lots of people think
“A fair test means being nice about it — giving both sides a proper go.”
The same idea somewhere new.
The thing you change is the independent variable. The thing you measure is the dependent variable. Everything you deliberately hold still is a control variable. The long names all mean the same simple thing: change one, measure one, freeze the rest.
Practice makes it stick.
The Ramp Test
Problem 1 of 1
Ben wants to know if a steeper ramp makes a car roll further. He makes the ramp steeper and also swaps to a heavier car. Is this a fair test?
1 of 4
In a fair test, how many variables do you change at once?
2 of 4
You want to test whether the surface changes how far a block slides. What must you keep the same?
3 of 4
Match each part of an experiment to its job.
Tap a card on the left to start.
4 of 4
Why write down what you kept the same?
Show what you know.
Question 1 of 1
You change two things at once and get a result. What can you conclude?
Claim, evidence, then reasoning.
The question
You ran it once the unfair way and once the fair way. Write an argument answering the question: which of your runs can tell you what a bigger pull does, and which cannot?
Evidence you can use
Fill in all three boxes. The reasoning box is the one that matters most.