Is Newton's Third Law Always True? Physics Explained Simply

What Does Newton's Third Law Actually Say?

“For every action, there is an equal and opposite reaction.”
Yeah, we’ve all heard it, probably during a boring high school physics class. But the truth is, this little sentence packs a punch.

What it really means is:
If object A pushes on object B, then object B pushes right back on A — same force, opposite direction.

Simple, right? Push a wall, and it pushes you back. Jump off a boat, and the boat moves the other way. You slap a table — the table slaps back (gently, but yeah).

But hold on a sec. Is it always true? Like... always?

Classical Physics: Newton Never Misses (Almost)

Everyday examples where it works perfectly

From tennis balls bouncing off rackets to car crashes — Newton’s third law is absolutely spot on in most classical mechanics situations. Engineers use it, astronauts rely on it, and your legs use it every time you walk.

Here’s a fun one:
Ever watched a rocket launch? The engines push gases downwards, and the rocket zooms upwards. Textbook Newton.

So yeah, in daily life, Newton’s third law is pretty much king. But...

Friction and weird surfaces — tricky but consistent

Sometimes it looks like the law fails. Like when you push a cart on a bumpy surface and it doesn’t move. You think, “Hey! Where’s my reaction force?”
But no — the force is there. It’s just getting balanced out by friction or transferred in complex ways.

So still consistent. Just… not obvious.

When Newton's Third Law Gets Questioned

In electromagnetism: not so straightforward

Here’s where things start getting weird. In some electromagnetic interactions, forces between charged particles don't always appear to be equal and opposite — at least not instantly.

For example, a moving electric charge creates a magnetic field. That magnetic field can affect another charge at a distance. But the “reaction force”? It might not show up right away.

Still, when you include the momentum of the field itself, everything adds up. So... yeah, Newton still kinda wins, but it’s more complicated than “you push, it pushes back.”

In quantum physics: things get funky

At the quantum scale? Oof, Newton’s third law feels outdated. Particles don’t behave like little billiard balls. They’re more like fuzzy clouds of probability.

Sometimes, in quantum field theory, interactions seem to violate Newton’s third law temporarily. But then again, quantum systems obey conservation of momentum, which is closely related — if not identical — to what Newton was saying.

It’s just... messier. Like, imagine trying to play ping-pong with invisible paddles that teleport. That level of messy.

What About Relativity? Another twist

Einstein’s theory of relativity introduced a new framework. Instead of forces, it talks more about spacetime curvature and energy-momentum.

Now here's the twist: Newton’s third law can appear to fail in relativistic contexts — like when objects move at speeds close to the speed of light. The action and reaction might not be simultaneous due to time dilation. Mind-bending stuff.

Still, conservation laws (momentum, energy, etc.) continue to hold — which keeps Newton’s third law functionally relevant, even if not literally perfect.

So... Is It Always True or Not?

It depends how deep you go

At the macroscopic, everyday scale? Absolutely yes. Newton’s third law is rock-solid. Push something, expect a push back — always.

In microscopic or high-speed environments? Ehh, kinda. Newton’s law needs adjustments. Physics has evolved, and so have the rules — or rather, we’ve found exceptions and expanded the framework.

Fun fact: Some modern physics textbooks don’t even teach Newton’s laws as fundamental anymore. They start with conservation laws and symmetry principles. Wild, huh?

Final Thoughts: Newton Was a Genius, But Not a God

So, is Newton’s third law always true?
Not exactly. But it’s damn close.

In everyday life, it’s your best bet. In advanced physics, it gets replaced or reframed by deeper theories. But don’t ditch Newton — his laws still form the backbone of our understanding of forces and motion.

Like that friend who isn’t perfect, but who always shows up when you really need them. That’s Newton’s third law.

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How Tall Should a 12 Year Old Be? We can only speak to national average heights here in North America, whereby, a 12 year old girl would be between 137 cm to 162 cm tall (4-1/2 to 5-1/3 feet). A 12 year old boy should be between 137 cm to 160 cm tall (4-1/2 to 5-1/4 feet).

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