Physics 1A: Scientific Processes & Measurement

Physics lab safety — quieter than chemistry, still serious

Physics labs do not look dangerous. There are no fuming acids, no open flames on most benches, no smells of chlorine. That is exactly why physics safety gets underweighted — the hazards are quieter but real. Batteries can short and heat up. Spring-loaded devices can launch metal. Ripple tanks tip over. Ballistic carts release stored energy. Lasers reflect off shiny surfaces. Every CBE question that asks about safe practices is really asking whether you have thought about what could go wrong before you touched the equipment.

The four pillars the CBE expects you to know:

• Personal protective equipment — safety goggles when a projectile, spring, or laser is in use. Closed-toe shoes for any bench with mass on it. Long hair tied back around rotating or ballistic apparatus.
• Electrical caution — check for damaged insulation before energizing. Never touch bare wire on an energized circuit. Discharge capacitors before handling. Voltages above 50 V DC can cause serious harm; treat them with respect regardless of the current rating.
• Thermal awareness — resistors, incandescent lamps, and heating elements are hot after use even when they look cool. Give them time to cool before touching.
• Environment and disposal — batteries, mercury thermometers, and other lab supplies are hazardous waste when discarded. Follow the disposal protocol posted in your room — never a household trash bin.

Under TEKS §112.39(c)(1), at least 40% of instructional time is expected to be laboratory or field investigation. That is the state saying safety is not optional — it is a scored skill.

The scientific method as a discipline, not a checklist

The scientific method is easy to memorize as a numbered list. It is harder to actually use. The point of the method is not the sequence of steps but the underlying rule: do not fool yourself, and do not let others fool you. It runs:

1. Observation — record what happened using specific numbers and units. "The cart moved faster" is not an observation. "The cart's velocity increased from 0.20 m/s to 0.55 m/s over 3.0 s" is.
2. Hypothesis — a testable statement, ideally in the form "if I change X, then Y will happen because Z." A hypothesis you cannot test with data is not a hypothesis; it is a wish.
3. Experiment — vary one thing (the independent variable), measure the response (the dependent variable), and hold everything else steady (controls). If you change two things at once, you cannot say which caused the effect.
4. Analyze — look at the actual data. Does the trend match your hypothesis? Any surprises are more interesting than confirmations.
5. Conclusion — accept, reject, or refine the hypothesis. Then invite others to reproduce your work. Science only holds when it can be reproduced independently.

Two words the CBE will test:

• Hypothesis — a single testable proposal, often revised or rejected.
• Theory — a broad explanation that has been tested repeatedly under many conditions and survived. In everyday English "theory" means "guess." In science it means the opposite: an explanation that has earned durability. Newton's theory of universal gravitation, kinetic molecular theory, quantum theory — these are not speculations. They are frameworks that have withstood a century or more of attempted refutation.

A hypothesis can be wrong and disappear overnight. A theory that lasts becomes the way physicists frame the problem.

SI units and scientific notation — a common language

Physics uses the International System of Units (SI) so that a measurement made in Texas is comparable to one made in Tokyo. The seven base units matter, but you will use only a few day to day:

• meter (m) — length
• kilogram (kg) — mass. Note: kg, not g, is the base unit.
• second (s) — time
• ampere (A) — electric current
• kelvin (K) — thermodynamic temperature
• mole (mol) — amount of substance
• candela (cd) — luminous intensity (used rarely in this course)

Derived units are combinations you already know: force is measured in newtons (N = kg·m/s²), energy in joules (J = kg·m²/s²), power in watts (W = J/s). Getting units right is not cosmetic. On the CBE, a numerically correct answer with the wrong unit is often scored as wrong. Habit: write units alongside numbers throughout every calculation, and check that they combine to the expected result. This is called dimensional analysis and it will catch about half of your careless algebra mistakes before the answer is written down.

Scientific notation lets you write very large and very small numbers without a page of zeros. The form is always:

a × 10ⁿ, where 1 ≤ a < 10

So the mass of an electron, 0.000 000 000 000 000 000 000 000 000 000 911 kg, is written 9.11 × 10⁻³¹ kg. The distance from the Earth to the Sun, roughly 149 600 000 000 m, is 1.496 × 10¹¹ m. Coefficient always between 1 and 10; exponent handles the scale. Getting the exponent sign wrong is the most common mistake — negative for very small, positive for very large.

Precision, accuracy, and significant figures

These three ideas overlap in everyday speech but have distinct technical meanings:

• Accuracy — how close a measurement is to the actual value. Missing the target by 3 cm is inaccurate; missing it by 0.3 mm is accurate. Accuracy is about correctness.
• Precision — how close repeated measurements are to each other, regardless of whether they are correct. Five shots that all land within 2 mm of each other are precise. If they all land 3 cm off-center, they are precise but inaccurate.
• Significant figures — the digits in a measurement that actually convey information. If you measured a table with a meter stick to 1.24 m, three significant figures is honest. Writing 1.24000 m implies your meter stick could resolve to the hundred-thousandth of a meter — it cannot.

Rules for significant figures that show up on the CBE:

• Non-zero digits are always significant: 24.7 has three sig figs.
• Zeros between non-zero digits are significant: 205 has three sig figs.
• Leading zeros (before the first non-zero digit) are not significant: 0.0032 has two sig figs.
• Trailing zeros are significant only if a decimal point is present: 2500 could be 2, 3, or 4 sig figs depending on context; 2500. has four; 2.500 × 10³ has four unambiguously.

When multiplying or dividing, the result carries as many sig figs as the least-precise input. When adding or subtracting, match the least-precise decimal place. These rules exist to prevent your answers from claiming more precision than the measurements deserved.

Uncertainty is part of the answer

Every measurement has an uncertainty. A stopwatch reading 3.42 s carries an uncertainty of about ±0.01 s because that is the smallest interval it can resolve. A metric ruler measuring 15.3 cm carries an uncertainty of about ±0.1 cm. A digital multimeter reading 4.55 V carries an uncertainty listed in its documentation. The CBE will ask questions that treat measurements as bracketed intervals rather than perfect points, and expect you to reason about whether a difference (say, 4.50 V vs 4.55 V) is meaningful or lies within the noise.

Two sources of error to recognize:

• Random error — small variations from measurement to measurement. Reduced by averaging many trials.
• Systematic error — a consistent bias in one direction (e.g., a clock that runs slow, a scale that reads 0.2 g high). Not reduced by averaging; you have to identify and correct the cause.

Reading motion from graphs

Physics problems live in equations, but you will encounter data in graphs. Two graph types anchor Physics 1A:

• Position vs time — the slope at any point is instantaneous velocity. A straight line means constant velocity. A curved line means acceleration.
• Velocity vs time — the slope at any point is instantaneous acceleration. The area under the curve (between the line and the time axis) equals the displacement. A horizontal line means constant velocity, zero acceleration. A sloped line means acceleration, and the area under it computes to a distance.

Reading these two graphs is a skill the CBE tests directly. If you can look at a v-t graph and shade the region whose area you need, you will not lose points to graph problems. If you cannot, the CBE will find that gap fast.

Check yourself

Before moving on, verify you can do each of the following without checking notes:

1. State the four laboratory safety pillars for a physics setting.
2. Explain the difference between a hypothesis and a theory in scientific usage.
3. Name the SI base units for length, mass, time, and current.
4. Write 0.00000521 m and 6 320 000 000 m in scientific notation.
5. Distinguish accuracy from precision using an example.
6. Given a velocity vs time graph, describe what the slope and the area under the curve each represent.

If any of these takes more than a beat, revisit that section before attempting practice questions.

Practice with CBE-style questions

The best next step is practice on the concepts above. Head to the practice bank filtered by Scientific Processes & Measurement for questions modeled after the Physics Semester A CBE. Every one has a full worked solution — not just the answer.

Independent practice content aligned to Texas Essential Knowledge and Skills (TEKS) §112.39. Not affiliated with TTU K-12, UT High School, UT-Austin, the Texas Education Agency, or any Credit by Examination administrator. Texas CBE™ does not administer any exam or grant academic credit.