Measurements in Physics | Interactive Lesson

The Nature of Science

Physics: An Experimental Science

Physics is based on observations of the physical world. Scientists develop models and theories to explain these observations. These theories are then tested through experimentation. If evidence contradicts a theory, it must be refined or replaced.

Evidence-Based

Scientific knowledge is derived from reproducible evidence rather than authority. This requires precise measurements and standardized units to ensure consistency across the global community.

Modeling Reality

Models are mathematical or conceptual simplifications of complex systems. They help us make predictions—like Fermi's estimations—that can be verified through rigorous data collection.

Fundamental vs Derived Units

The SI Fundamentals

Every measurement in the universe is built from 7 base units. Here are the core 5 we focus on:

Length meter (m)

Mass kilogram (kg)

Time second (s)

Current ampere (A)

Temperature kelvin (K)

Derived Units

Derived units are combinations of fundamental units. For example, Force (F = ma) is measured in Newtons (N).

1 N = 1 kg ⋅ m/s²

Force = Mass × Acceleration

Interactive Task: Unit Deduction

Drag the fundamental unit components to match the derived quantities.

Force (F = ma)

Pressure (P = F/A)

Energy (E = F ⋅ d)

Power (P = E / t)

Fundamental Parts

kg

m

m⁻¹

m²

s⁻²

s⁻³

Significant Figures

Non-Zeroes

Always significant.
54,768 (5 sig figs)

Sandwiched Zeroes

Always significant.
102 (3 sig figs)

Leading Zeroes

Never significant.
0.0001 (1 sig fig)

Sig Fig Calculator & Practice

Orders of Magnitude

Relative Scale Exploration

Rounding numbers to the nearest power of 10. Can you match these?

Mass of an adult human

Diameter of an atom

Mass of the Earth

Mass of an apple

The Art of Estimation

Enrico Fermi

Enrico Fermi was famous for his rapid approximations. During the Trinity nuclear test (1945), he dropped scraps of paper as the blast wave passed. By measuring how far they were blown, he estimated the blast energy within minutes—while colleagues were still waiting for complex calculations.

Trinity Estimation

Radius at 0.025s: 100m

Air Density: 1.2 kg/m³

Challenge: Grains of Sand

How many grains of sand would fill the volume of the Earth?

Challenge: Hair Growth

Estimate the speed of human hair growth in m/s.

Knowledge Check

1. Why is it important to have the SI (Système Internationale d'Unités) system?

It uses English units which are easier to visualize.

It ensures universal communication and consistent comparison of scientific data.

It is the only system that allows for measurement of time.

It makes all numbers in physics integers.

2. Is it possible for two quantities to have the same dimensions but different units?

Yes (e.g., miles and meters both measure the dimension of length).

No, units and dimensions must have a one-to-one relationship.

Yes, but only in the Imperial system.

No, because dimensions are calculated from units.

3. Which of the following is a fundamental SI unit?

Joule (J)

Newton (N)

Ampere (A)

Watt (W)

4. Which of the following lists contains only fundamental units?

kilogram, tesla, kelvin

ampere, second, candela

newton, metre, ampere

mole, second, joule

5. Which of the following is a derived unit?

Pascal (Pa)

Mole (mol)

Kelvin (K)

Candela (cd)

6. How many significant figures are in 1546?

2

3

4

5

7. How many significant figures are in 0.0407?

2

3

4

5

8. How many significant figures are in -200.0?

1

2

3

4

9. In the equation T = 2π√(m/k), where T is time and m is mass, what is the dimension of the spring constant k?

kg/s² (Mass / Time²)

kg ⋅ s (Mass ⋅ Time)

s/kg (Time / Mass)

m/s² (Acceleration)

Learning Objectives