Does the strong force reach right across a single atomic nucleus?
The Sun's gravitational force reaches Earth, 150 million km away. Yet the strongest force in nature cannot reach even from one atom's nucleus to the next. How strong a force is and how far it reaches are different questions.
The last lesson ranked the forces by strength. This lesson sorts them by the other question: how far each force reaches. There are only two bins. Watch the four forces sort themselves.
The Sun's gravitational force still acts at 150 million km. So the gravitational force goes in the long bin.
A charged balloon attracts your hair across a gap, and its force would still act, ever more weakly, at any distance. So the electromagnetic force goes in the long bin too.
But a quark in one atom's nucleus and a quark in the neighboring atom's nucleus feel no strong force between them, because the strong force acts only over distances about the size of an atomic nucleus or smaller. So the strong force goes in the short bin.
And the weak force also acts only over distances about the size of an atomic nucleus or smaller. So the weak force goes in the short bin too.
Now name the bins. A force that keeps acting at any distance, growing weaker but never reaching zero, is called an unlimited-range force. A force that acts only over distances about the size of a nucleus or smaller is called a nuclear-range force.
Each bin holds two forces. Range says nothing about strength.
Gravitational and electromagnetic are unlimited-range; strong and weak are nuclear-range. Range is not strength: the strong force is the strongest of the four AND one of the two shortest-ranged. To sort by range, read the force's range line and nothing else.
Is the electromagnetic force unlimited-range or nuclear-range?
Recall its range line: the electromagnetic force acts over unlimited range, growing weaker with distance but never reaching zero.
A force that keeps acting at any distance is unlimited-range.
The electromagnetic force is unlimited-range.
The weak force is weaker than the electromagnetic force. Does that make it shorter-ranged?
Strength and range are separate questions. A sort by range reads only the range line.
The weak force's range line says it acts only over distances about the size of an atomic nucleus or smaller.
The weak force is nuclear-range because of its range line, not because of its weakness.
Quick-fire drill
Here are six quick sorts. The two options are the same each time: unlimited-range or nuclear-range.
Is the force that binds quarks unlimited-range or nuclear-range?
Is the force that changes one type of particle into another unlimited-range or nuclear-range?
Is the gravitational force unlimited-range or nuclear-range?
Is the electromagnetic force unlimited-range or nuclear-range?
However far apart two particles sit, this force still acts. Which range class is it?
A student sorts by strength and calls the strong force unlimited-range. Which class is it?
Your turn
Which pair contains both nuclear-range forces?
Which statement describes an unlimited-range force?
Because of its strength, a student expects the strong force to reach the farthest of the four. Which statement about the strong force's range is correct?