Fun to Imagine | Jiggling Atoms

Duration 06:41
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⭐ Interactive Lesson ⭐
Richard Feynman - Jiggling Atoms

Jiggling Atoms

"Nothing is really as it seems. We used to get hot and cold, and all that... but hot and cold are just the speeds that the atoms are jiggling."

Imagine a cup of coffee sitting on a table. The atoms in the coffee are jiggling a great deal. They bounce against the cup, the cup shakes, and that jiggling spreads to the table. That is what heat is: the spreading of irregular motion. It is easy to understand if you just imagine it.

How do we know atoms exist if we cannot see them? We know because of Brownian Motion. Long before we could image atoms, scientists saw pollen grains jiggling in water - pushed by invisible atomic collisions. This was the first proof that the jiggling is real.

The Perpetual Jiggle

Let us imagine these atoms. They have perfect elasticity - they never lose any energy. They are perpetually moving. Use the Temperature Slider to change how much they jiggle, and observe how they change from a solid, to a liquid, to a gas.

(You can also drag the gray piston wall directly with your mouse!)

Cold (Solid) Warm (Liquid) Hot (Gas)
Compressed Expanded

Observation Log:

The atoms are locked in place, like oranges in a crate. This is a solid.

Notice what happens when you compress the piston quickly. The atoms hit the moving wall and pick up speed - they get hotter! This is why a bicycle pump gets hot when you pump it. You are physically pushing energy into the gas.

Conversely, when the piston expands (moves out), the atoms hit a retreating wall and lose speed. This is why gases cool down when they expand.

Advanced Investigation: Surface Tension

Now, look at a water drop. The atoms like to be next to each other; they want as many partners as they can get. The guys at the surface are very unhappy - they have partners on one side, but only air on the other.

They are nervous and keep pounding inwards, trying to get inside where the friends are. This pulls the surface tight, creating a sphere.

Try This: Move your mouse inside the box to "Disturb" the drop and break the tension!

The "unhappy" surface atoms (Red) pulling inwards to the "happy" interior atoms (Blue).

A Test of Imagination

There is no teacher to grade you, but let us see if you can imagine what is happening.

Science Since the 80s

When this episode of Fun to Imagine aired in 1983, the idea of "Zero Point Energy" was already a known hypothesis in Quantum Mechanics, dating back to 1911. Feynman knew that atoms "never lose energy."

However, it is only in the years since the 80s that we have been able to experimentally prove and measure this "Zero Point Energy" in macroscopic systems. We now have definitive proof that even at Absolute Zero (-273.15°C), where classical motion should stop, a fundamental "quantum jiggle" remains. The universe, at its heart, is always dancing.