recall the following SI base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K)

SI Base Quantities & Units 📏

1️⃣ Mass – Kilogram (kg)

Mass tells us how much matter is in an object. Think of it as the “weight” of a backpack that doesn’t change when you move it to the moon. The SI unit is the \$\text{kg}\$.

• 🔹 1 kg ≈ 2.2 lb (pounds)
• 🔹 A 1 kg rock is about the mass of a small watermelon.
• 🔹 In physics, mass is a measure of inertia – how hard it is to change motion.

2️⃣ Length – Meter (m)

Length measures distance. A meter is roughly the length of a school ruler or the height of a standard doorframe. The SI unit is the \$\text{m}\$.

• 🔹 1 m ≈ 3.28 ft (feet)
• 🔹 A 1 m stick is about the length of a typical smartphone.
• 🔹 In experiments, we often use meters to describe wavelengths, heights, and distances between objects.

3️⃣ Time – Second (s)

Time measures how long something lasts. A second is the time it takes for a light bulb to flicker once. The SI unit is the \$\text{s}\$.

• 🔹 1 s ≈ 1 second (obviously!)
• 🔹 60 s = 1 minute, 3600 s = 1 hour.
• 🔹 In physics, we use seconds to calculate speeds, frequencies, and decay times.

4️⃣ Electric Current – Ampere (A)

Current measures how many electrons flow through a conductor per second. Imagine a river of tiny charged particles. The SI unit is the \$\text{A}\$.

• 🔹 1 A = 1 C/s (coulomb per second)
• 🔹 A typical light bulb draws about 0.06 A.
• 🔹 In circuits, we use amperes to determine how much power is being used.

5️⃣ Temperature – Kelvin (K)

Temperature measures how hot or cold something is. Kelvin is the absolute scale starting at absolute zero, the coldest possible temperature. The SI unit is the \$\text{K}\$.

• 🔹 0 °C = 273.15 K
• 🔹 100 °C = 373.15 K (boiling point of water)
• 🔹 In physics, Kelvin is used to describe thermal energy, radiation, and statistical mechanics.

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