Physical constant facts for kids
A physical constant is a special number in science that always stays the same. It doesn't change, no matter where you are or when you measure it. Think of it like a fixed rule of the universe. This is different from a mathematical constant, which is just a number from math, not something we measure in the real world.
Many important physical constants help us understand how the universe works. Some famous ones include the speed of light, Planck's constant, the gravitational constant, and Avogadro's number.
Some scientists wonder if physical constants might slowly change as the universe gets older. However, there is no proof of this happening yet.
Constants that don't have units, like meters or seconds, are called fundamental physical constants. These are like pure numbers that describe basic properties of nature.
Some people believe that if these physical constants were even slightly different, there would be no life in the universe. They suggest that the universe seems to be fine-tuned perfectly for intelligent life to exist.
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What are Physical Constants?
Physical constants are like the unchanging ingredients or rules of the universe. They are numbers that scientists find through experiments and observations. These numbers describe basic properties of nature. For example, the speed of light tells us how fast light can travel.
These constants are very important for physical laws and theories. They help scientists predict how things will behave. Without them, our understanding of physics would be very different.
Famous Physical Constants
There are many physical constants, but some are more well-known because they are used so often.
Speed of Light (c)
The speed of light is the fastest speed anything can travel in the universe. It's a huge number, about 299,792,458 meters per second. This constant is key to Einstein's theory of relativity. It shows how energy and mass are connected.
Planck's Constant (h)
Planck's constant is used in quantum mechanics. This is the part of physics that studies very tiny things, like atoms and particles. It helps us understand how energy is transferred in small, specific packets called "quanta."
Gravitational Constant (G)
The gravitational constant tells us how strong the force of gravity is. Gravity is the force that pulls things together, like why an apple falls from a tree or why planets orbit the Sun. This constant helps scientists calculate the gravitational pull between any two objects.
Avogadro's Number
Avogadro's number is used in chemistry. It tells us how many particles (like atoms or molecules) are in a certain amount of a substance. It's a very large number, about 6.022 x 1023. This helps chemists measure and compare different substances.
Table of Physical Constants
This table shows some important physical constants, their symbols, and their measured values. The "Relative Standard Uncertainty" shows how precise the measurement is.
| Quantity | Symbol | Value | Relative Standard Uncertainty |
|---|---|---|---|
| speed of light |  |
299 792 458 m·s−1 | defined |
| constant of gravity |  |
6.67428(67) × 10−11m³·kg−1·s−2 | 1.0 × 10−4 |
| Planck's constant |  |
6.626 068 96(33) × 10−34 J·s | 5.0 × 10−8 |
| smallest electrical charge |  |
1.602 176 487(40) × 10−19 C | 2.5 × 10−8 |
| electron mass |  |
9.109 382 15(45) × 10−31 kg | 5.0 × 10−8 |
Related pages
See also
In Spanish: Constante física para niños
