Chapter 1: Scientific Study
Comprehensive Interactive Notes
Prepared By Deepak Prakash Bhatta
Quick Contents:
- Scientific study and why variables are important
- Full definitions of variables: independent, dependent, and controlled
- Memory diagrams and memory tips
- Experiment examples with variable identification
- Units: fundamental and derived units
- Unit analysis and validity of equations
- Solved textbook-style exercise answers and quick flashcards
One-page memory formula:
Scientific study = planned observation + measurable evidence + logical explanation.
Experiment = change one factor, observe one result, keep others same.
1. Scientific Study
Scientific study - A planned and organized study of objects, events, and phenomena in nature. It uses scientific facts, theories, models, experiments, physical situations, the scientific method, and empirical or measurable evidence.
Example: A scientist observes a wilted potted plant, asks why it wilted, tests water and sunlight conditions, and uses evidence to explain the cause.
Scientific study tries to answer questions such as: What happened? Why did it happen? Which factors caused it? How can the result be predicted?
- It is organized: the researcher follows a plan rather than guessing randomly.
- It is logical: conclusions must match observations and evidence.
- It is measurable: the result should be recorded using quantities and units whenever possible.
- It is repeatable: the same method should give similar results when repeated under the same conditions.
Causative factor: A factor that produces or influences an event or change. (e.g., Lack of water for wilting).
Effect: The result or change produced due to a causative factor. (e.g., Wilting of the plant).
Memory tip:
Cause answers "Why?" | Effect answers "What happened?"
Example: less water → wilting.
2. Variables of Scientific Research
Variable - A causative factor, characteristic, trait, or physical quantity that has a direct or indirect relationship with an event or phenomenon and whose value can change.
Example: In the rubber-band catapult experiment, extension of the rubber band and distance travelled by the paper bullet are variables.
2.1 Independent Variable
The variable that the researcher deliberately changes or manipulates in an experiment. It is the causative factor.
Example: Extension of the rubber band (4 cm, 6 cm, 8 cm, 10 cm).
2.2 Dependent Variable
The variable whose value depends on another variable. It is the observed effect or measured result of the experiment.
Example: Distance travelled by the paper bullet.
2.3 Controlled Variable
A variable kept the same throughout an experiment so that it does not affect the result. These make the experiment valid, reliable, and fair.
Example: Same rubber band thickness, same paper bullet size.
I-D-C memory code:
I = I change | D = Data I observe | C = Constant things I keep the same.
Fair test rule: Normally only ONE independent and ONE dependent variable. All others controlled.
2.4 Rules to Remember About Variables
- Use only one independent variable in one experiment.
- Measure only one main dependent variable for a clear conclusion.
- Control all other variables that may influence the result.
- In equations, the dependent variable is usually on the left side and the independent on the right. (e.g., s = vt, distance s depends on time t).
- In graphs, Independent = X-axis and Dependent = Y-axis.
Graph memory tip: X = what you change. Y = what you measure.
3. Experiment Examples
3.1 Activity: Rubber-band Catapult
Aim: To study how the extension of a rubber band affects the distance travelled by a paper bullet.
| Part | Details |
|---|---|
| Materials | Rubber band, 15 cm ruler, small paper pieces, measuring tape |
| Independent | Extension/stretch of rubber band: 4 cm, 6 cm, 8 cm, 10 cm |
| Dependent | Distance travelled by the paper bullet |
| Controlled | Same rubber band thickness, same paper bullet size, same release method, same angle, same place |
| Expected relation | When extension increases, distance increases. x ∝ e |
3.2 Identification of Variables Table
| Experiment | Independent (I) | Dependent (D) | Controlled variables (C) |
|---|---|---|---|
| Plant growth & sunlight | Amount of sunlight | Height/growth of plant | Same plant type, soil, water, manure, pot size |
| Plant growth & fertilizer | Amount/type of fertilizer | Plant height or mass | Same seed type, soil, water, sunlight, pot, time |
| Limestone & acid | Surface area of limestone | Rate of chemical reaction | Same acid concentration, volume, limestone mass, temp |
| Tap knob & water flow | Magnitude of knob rotation | Water flow per minute | Same water pressure |
| Electromagnet | Amount of electric current | Number of pins attracted | Same solenoid turns, same pin size |
| Heat & solubility | Temperature of water | Amount of sugar dissolved | Same water amount, same stirring method |
| Exercise & heartbeat | Duration of exercise | Number of heartbeats | Same exercise type, same time gap, same counting time |
3.3 Textbook-style Experiment Cases
| Case | Independent | Dependent | Controlled variables / Correction |
|---|---|---|---|
| Dry cell & wire thickness | Thickness of wire | Life span of dry cell | Same dry cell, same bulb, same wire material/length |
| Chandani: Soil mixtures | Type of substance (lime, urea, salt, compost) | Height/growth of plants | Same soil, pot, seed, water, sunlight. (Uses 3 pots for reliability) |
| Subodh: Flask color | Color of enamel coating (black, white, green, red) | Temperature of water after sunlight | Same flask, water volume, initial temp, exposure time |
| Manisha: Dog habits | Amount of food & time of feeding | Speed at which dog eats | Correction: Test only ONE at a time. Keep food constant while changing time, or vice versa. |
Warning: If two things are changed together, you cannot know which one caused the result. (Manisha's error).
4. Types of Units
Physical quantity: A quantity that can be measured and expressed with a number and a unit. (e.g., 2 m, 5 kg).
Unit: A standard quantity used for measuring a physical quantity. (e.g., metre).
4.1 Fundamental Units (SI 7)
Units that have independent existence and cannot be resolved into simpler forms.
| S.N. | Physical quantity | Fundamental SI unit | Symbol |
|---|---|---|---|
| 1 | Length | metre | m |
| 2 | Mass | kilogram | kg |
| 3 | Time | second | s |
| 4 | Temperature | kelvin | K |
| 5 | Luminous intensity | candela | cd |
| 6 | Electric current | ampere | A |
| 7 | Amount of substance | mole | mol |
SI 7 memory line: L-M-T-T-L-E-A (Length, Mass, Time, Temp, Luminous, Electric, Amount).
4.2 Derived Units
Units formed by combining two or more fundamental units according to a formula.
| Quantity | Formula | Unit analysis | Derived unit / symbol |
|---|---|---|---|
| Area | L × B | m × m | m² |
| Volume | L × B × H | m × m × m | m³ |
| Density | Mass / Vol | kg / m³ | kg m⁻³ |
| Velocity | Displacement / Time | m / s | m s⁻¹ |
| Acceleration | Velocity / Time | (m s⁻¹) / s | m s⁻² |
| Force | Mass × Accel | kg × m s⁻² | newton (N) = kg m s⁻² |
| Pressure | Force / Area | (kg m s⁻²) / m² | pascal (Pa) = kg m⁻¹ s⁻² |
| Work / Energy | Force × Dist | (kg m s⁻²) × m | joule (J) = kg m² s⁻² |
| Power | Work / Time | (kg m² s⁻²) / s | watt (W) = kg m² s⁻³ |
| Moment | Force × Dist | (kg m s⁻²) × m | N m = kg m² s⁻² |
| Frequency | 1 / Time | 1 / s | Hz = s⁻¹ |
4.3 Difference: Fundamental vs Derived
| Fundamental Unit | Derived Unit |
|---|---|
| Does not depend on other units. | Depends on fundamental units. |
| Cannot be broken into simpler forms. | Can be expressed as a combination of fundamental units. |
| Only seven SI fundamental units. | Many derived units exist. |
| Examples: m, kg, s, K, cd, A, mol. | Examples: N, Pa, J, W, m², m³, kg m⁻³. |
5. Analysis of Unit-wise Equations
Unit analysis - A method used to check the validity of a formula by comparing units on the LHS and RHS. For a valid equation, both sides must have the same unit composition.
Rules:
- Write equation clearly.
- Replace quantities with SI units.
- Simplify both sides.
- If LHS = RHS, it is dimensionally valid.
Limitation: Can prove an equation is impossible, but cannot prove exact numerical constants (like 1/2) are correct.
5.2 Worked Examples
| Equation | Unit analysis | Result |
|---|---|---|
| s = v × t | m = (m s⁻¹) × s = m | Valid |
| s = v / t | m ≠ (m s⁻¹) / s = m s⁻² | Invalid |
| v² = u² + 2as | m² s⁻² = m² s⁻² + (m s⁻²)(m) = m² s⁻² | Valid |
| s = ut + ½at² | m = (m s⁻¹)(s) + (m s⁻²)(s²) = m + m | Valid |
| s = ut + ½a²t | m ≠ m + (m s⁻²)² × s = m + m² s⁻³ | Invalid |
| v² = ut | m² s⁻² ≠ (m s⁻¹)(s) = m | Invalid |
Addition/subtraction rule: You can only add/subtract quantities with the same unit composition. (e.g., u + v is OK, but s + at is NOT).
6. Solved Practice and Exercise Answers
6.1 Choose the Correct Option
- Fundamental unit: Kilogram (SI unit of mass).
- Quantity with unit m s⁻¹: Velocity (Displacement/Time).
- Derived unit: Joule (Unit of work/energy).
- Unit denoting Newton: kg m s⁻² (Force = mass × accel).
6.2 Give Reasons
Q: Why is joule a derived unit?
A: Work = force × distance. Unit = (kg m s⁻²) × m = kg m² s⁻². Since it is formed from kg, m, and s, it is derived.
Q: Why should some variables be controlled?
A: To make the experiment fair, valid, and accurate by ensuring only the independent variable affects the result.
Q: Why is v² = ut not valid?
A: LHS unit (m² s⁻²) ≠ RHS unit (m). Since units don't match, it is invalid.
6.3 Short Answer Bank
- Unit: Standard quantity used for measuring physical quantities.
- SI Units: Mass = kg, Temp = K, Energy = J, Density = kg m⁻³.
- Validity check: By unit analysis (comparing LHS and RHS).
- Fundamental units in Pressure: kg, m, s (Pa = kg m⁻¹ s⁻²).
- Units in Newton: kg m s⁻².
- Units in Watt: kg m² s⁻³.
- Units in Joule: kg m² s⁻².
- Units in Pascal: kg m⁻¹ s⁻².
6.4 Formula Validity Practice
- Power P = mv²: Invalid (RHS is Joule, Power is Watt).
- Pressure P = mv/A: Invalid (RHS units don't match Pascal).
- Ohm proof: Ohm = kg m² s⁻³ A⁻².
7. Quick Flashcards
Last-minute Revision Checklist
- Can I define scientific study, variable, unit, fundamental unit, and derived unit?
- Can I identify independent, dependent, and controlled variables from a story?
- Can I explain why controlled variables are needed?
- Can I place independent and dependent variables on a graph?
- Can I list all 7 SI fundamental units with symbols?
- Can I derive N, Pa, J, W, and ohm from fundamental units?
- Can I check whether an equation is valid by unit analysis?
Exam answer pattern: Definition + example + reason = strong answer. For experiments, write I, D, C in separate lines.
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