Nature of science · physics · 45 minutes

Build a Hypothesis

A hypothesis says what you think will happen in a test. Learn the if–then pattern, try several examples, and use evidence to check your idea.

Today’s target: write a clear hypothesis and identify the change and expected result.

Hypothesis: If I change ___, then ___ will happen.

Built from NGS Magnified, “The Method of Science.” Source wording and figures are attributed; the ramp investigation and teaching sequence are original to this class.

0:00–0:05 · 5 minutes

The suspicious race

I ran an experiment to find out whether a steeper ramp makes a toy car reach the finish sooner. Here is what I did. Do you trust my result?

🚙

Trial A · gentle ramp

Blue car · 1 metre · carpet
Time: 2.4 s

🏎️

Trial B · steep ramp

Different car · 1.5 metres · tile
Time: 1.2 s

Measure first · no teaching yet

Does this race prove that the steeper ramp made the car faster?

Besides the ramp angle, what else is different between Trial A and Trial B?

1. Name the question: does ramp steepness change travel time?

2. Compare the trials: car, distance, and surface also changed.

3. Any of those changes could explain the time.

B. The result is real, but its cause is not identified. A picks a smaller number without asking what produced it. C notices a winner but gives the wrong reason. The check to carry forward is: did we change only the thing named in the question?

Control: A result cannot identify a cause when several possible causes changed. Mother: comparison—notice what is the same and different. Placement is recorded silently; do not repair it yet.

0:05–0:10 · 5 minutes

What is a hypothesis?

A hypothesis says what you think will happen in a test.
Write it: If I change ___, then ___ will happen.

The if part says what you will change. The then part says what you expect to observe or measure. A hypothesis must be testable: we must be able to run a test and collect evidence that could support it or show that it needs changing.

Lost on “testable”?

Testable means we can do something and observe the result. “If I raise the ramp, then the car will take less time” is testable. “Blue cars are happier” is not testable because we have no clear way to measure “happier.”

Is a hypothesis just any if–then sentence?

No. “If today is Wednesday, then tomorrow is Thursday” is an if–then sentence, but it does not predict the result of a test. A science hypothesis connects a change to a result we can observe or measure.

Scientific method diagram from NGS Magnified — A hypothesis comes after the question and before the experiment.

0:10–0:20 · 10 minutes

See the pattern

Plants

If I give a plant more hours of light, then it will grow taller in one week.

Change: hours of light · Measure: height

Ice

If I add salt to ice, then the ice will melt in less time.

Change: salt · Measure: melting time

Pendulum

If I make a pendulum’s string longer, then one swing will take more time.

Change: string length · Measure: swing time

Our ramp

If I raise the ramp, then the car will take less time to reach the finish.

Change: ramp height · Measure: travel time

How do I find the two blanks?

First ask, “What will I change on purpose?” Put that after if. Then ask, “What result will I watch or measure?” Put that after then.

Try one together

Which sentence is the clearest testable hypothesis?

Look for one change and one result that can be measured.

1. Find the if: raise the ramp.

2. Find the then: the measured travel time becomes shorter.

3. Both parts can be tested, so B is a hypothesis.

B. It names exactly what changes and what measurable result is expected. A and C are opinions, not predictions. D uses if–then, but the result is a personal preference rather than evidence from a physical test.

0:20–0:31 · 11 minutes

Build and test our hypothesis

Our hypothesis: If I raise the ramp, then the car will take less time to reach the finish.

To test that idea fairly, we change the ramp height and measure the travel time. We keep the car, surface, distance, and release the same.

What do “independent” and “dependent” mean?

The independent variable is what we choose to change: ramp height. The dependent variable is the result we measure: travel time. The time depends on what happens when the ramp changes.

Why keep the other things the same?

If we also change the car, surface, distance, or push, we will not know which change caused the result. A fair test gives our hypothesis one clear test.

Worked → faded

Which plan can answer our ramp question?

Which plan gives ramp height only one rival explanation: none?

Fire · Duplicate: write the question without changing its words.

Metal · Transcribe: change = ramp height; measure = travel time.

Wood · Rearrange: hold car, surface, distance, and release constant.

Earth · Collapse: only plan C does this.

Water · Meaning: a time difference now has one plausible experimental cause.

C. A changes the push, B changes the car, and D supplies no comparison. C changes ramp height, measures travel time, and keeps the other conditions constant. Control: one fair change. Mother: noticing sameness and difference.

Distractors: A confuses force supplied by hand with ramp effect. B recognizes comparison but not fair comparison. D confuses careful measurement with an experiment. Ask the student to say “change, measure, hold” before using the vocabulary.

Faded

Complete the experiment aloud: “We change _, measure _, and keep ___ the same.”

The independent variable is the one the investigator chooses before the car moves.

Find the deliberate change.

Find the response that gets measured.

List every other possible cause that must be held still.

A. Ramp height is independent; time is dependent; car, distance, surface, and release are constants. B reverses cause and response. C changes the car and fails to isolate ramp height.

Control: change, measure, hold. Mother: the fair-test plan immediately above. Mark satisfied when the student can say the sentence without the formal vocabulary.

0:31–0:38 · 7 minutes

Let evidence answer

We ran each condition three times. Repetition does not guarantee truth; it shows whether the pattern survives another try.

Ramp height	Trial 1	Trial 2	Trial 3	Mean
10 cm	2.5 s	2.4 s	2.6 s	2.5 s
20 cm	1.9 s	2.0 s	1.8 s	1.9 s
30 cm	1.5 s	1.4 s	1.6 s	1.5 s

Bare

Which conclusion says exactly what the evidence supports—and no more?

Which answer stays inside the objects, distances, and conditions we actually tested?

Describe the pattern: height increased while mean time decreased.

Limit the claim to this setup.

Say “supported,” not “proved forever.”

B. It reports the observed relationship and its boundary. A leaps to every object. C treats evidence as permanent proof. D mistakes a mean of variable measurements for an exact inevitable result. Control: the claim cannot be larger than the test.

Mother: fair-test design. Control: claim ≤ evidence. If missed, point to the words “in this setup”; do not add another calculation.

0:38–0:43 · 5 minutes

Five more hypotheses to test

For each one, ask two questions before opening it: What changes? and What do we measure?

1 · Does drop height change bounce height?

Hypothesis: If I drop the same ball from a greater height, then it will bounce higher.

Test: Drop the same ball onto the same floor from 50 cm, 100 cm, and 150 cm. Do not throw it. Measure the height of the first bounce.

Change: drop height · Measure: bounce height

2 · Does water temperature change dissolving time?

Hypothesis: If I raise the water temperature, then the sugar will dissolve in less time.

Test: Put the same amount of sugar into equal amounts of cold, warm, and hot water. Stir each one in the same way and time how long the sugar takes to disappear.

Change: water temperature · Measure: dissolving time

3 · Does pendulum length change swing time?

Hypothesis: If I make a pendulum’s string longer, then ten swings will take more time.

Test: Use the same weight and release angle with three string lengths. Measure the time for ten complete swings.

Change: string length · Measure: time for ten swings

4 · Do stacked magnets lift more paper clips?

Hypothesis: If I stack more identical magnets together, then they will lift more paper clips.

Test: Try one, two, and three magnets with the same kind of paper clips. Count how many clips each stack can lift.

Change: number of magnets · Measure: number of paper clips lifted

5 · Does paper-airplane wing size change flight time?

Hypothesis: If I make the wings wider, then the paper airplane will stay in the air longer.

Test: Make planes from the same paper with the same basic fold but different wing widths. Launch them from the same place in the same way. Measure time in the air.

Change: wing width · Measure: flight time

Lost on how these are fair tests?

Each test changes one named thing, measures one result, and keeps the other important conditions the same. That lets the evidence speak directly to the hypothesis.

0:43–0:45 · 2 minutes

Close and seed

Finish these two sentences in your own words:
1. A hypothesis is ___.
2. If I change ___, then ___ will happen.

Next time: we will use the evidence to decide whether our ramp hypothesis was supported.