# Scientific Method and Experimental Design

Physics I · Principles of Laboratory Practice · https://tryals.app/learn/physics-i/scientific-method-and-experimental-design

## The Scientific Method

The **scientific method** is the systematic approach to acquiring reliable knowledge through structured inquiry. It turns raw observation into validated fact.

**The Five Steps**
1. **Observe** a phenomenon and ask a **question**.
2. Propose a **hypothesis**, which is a testable prediction.
3. Design a controlled **experiment**.
4. Collect and **analyse** data.
5. Draw **conclusions**.

| Variable | Definition | Example |
| --- | --- | --- |
| **Independent** | Variable you change | Applied voltage |
| **Dependent** | Variable you measure | Current in wire |
| **Controlled** | Variables held constant | Temperature |

**Reproducibility**: Results must be **repeatable** in the same lab and **reproducible** in different labs to be deemed reliable.

## Hypotheses & Pitfalls

**Null Hypothesis**: Always assume no effect exists ($H_0$). The goal of testing is to **reject** $H_0$ with statistical confidence, never to "prove" an absolute truth.

| Concept | Principle |
| --- | --- |
| **Verification** | Experiments fail to disprove; they never prove |
| **Falsifiability** | Must allow for a possible contradiction |

**Key Insight**: A good experiment doesn't prove a hypothesis; it fails to disprove it. One single contradicting observation can overturn a theory entirely.

**Common Pitfall**: An experiment that cannot fail is not an experiment. If no conceivable data can count against your hypothesis, your procedure tests nothing.

## Practice questions

7 of this lesson's 11 practice questions, with answers. The full set is in the app.

### 1. A scientific hypothesis must be testable and falsifiable.

**Answer:** True

**Why:** Falsifiability is the hallmark of a scientific hypothesis; it must make predictions that can be proven wrong.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/a-scientific-hypothesis-must-be-testable-and-falsifiable

### 2. An experiment yields five measurements: 10.2, 10.5, 10.3, 10.4, 10.1. What is their mean? **Set the slider to your answer.**

**Answer:** 10.3 (within ±0.309)

**Why:** Mean = (10.2 + 10.5 + 10.3 + 10.4 + 10.1)/5 = 51.5/5 = 10.3.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/an-experiment-yields-five-measurements-10-2-10-5-10-3-10-4-10-1

### 3. A hypothesis that no observation could contradict is considered scientifically useless, however true it might be. Why is that?

A. Because a claim compatible with every outcome forbids nothing
B. Because untestable claims are always false
C. Because scientists lack the instruments to test such claims at present
D. Because such claims cannot be expressed mathematically

**Answer:** A. Because a claim compatible with every outcome forbids nothing

**Why:** Content is what a claim rules out. A statement consistent with every possible result carries no information about which result will occur, so no experiment can bear on it.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/a-hypothesis-that-no-observation-could-contradict-is-considered

### 4. Which are essential features of a well-designed controlled experiment?

A. As many variables changed simultaneously as possible
B. Repeated trials for reliability
C. A control group for comparison
D. Only one independent variable changed at a time

**Answer:** B. Repeated trials for reliability; C. A control group for comparison; D. Only one independent variable changed at a time

**Why:** Controlled experiments isolate one variable, include a control group, and use repeated trials.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/which-are-essential-features-of-a-well-designed-controlled-experiment

### 5. Sort each item into the correct variable type for a plant-growth experiment where light intensity is varied.

**Answer:**

- Independent: Light intensity
- Dependent: Plant height after 2 weeks, Number of leaves
- Controlled: Soil type, Water amount per day, Room temperature

**Why:** Light is varied, growth metrics are measured, everything else is held constant.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/sort-each-item-into-the-correct-variable-type-for-a-plant-growth

### 6. Sort each statement: is it a **testable hypothesis** or not?

**Answer:**

- Testable hypothesis: Doubling the pendulum length increases its period by a factor of √2, Air resistance reduces this projectile’s range by more than 5%
- Not testable: This lab setup is elegant, The ball falls because it is its nature to fall

**Why:** Falsifiability is the entry ticket to science: a real hypothesis sticks its neck out with a measurable prediction. Statements of taste or circular "explanations" cannot lose, and therefore cannot teach us anything.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/sort-each-statement-is-it-a-testable-hypothesis-or-not

### 7. A control group receives no treatment, which produces no data about the treatment. Why is it nevertheless essential?

A. Because it doubles the sample size and so improves precision
B. Because ethical guidelines require an untreated comparison group
C. Because it allows the experiment to be repeated later
D. Because it shows what would have happened anyway

**Answer:** D. Because it shows what would have happened anyway

**Why:** The control supplies the baseline the effect is measured against. Without it you have a before-and-after, which cannot distinguish the treatment from everything else that happened meanwhile.

Page: https://tryals.app/practice/physics-i/scientific-method-and-experimental-design/a-control-group-receives-no-treatment-which-produces-no-data-about