Newton's Third Law
Every interaction creates two forces:
equal in size, opposite in direction, on different objects.

Action 20 N ↔ Reaction 20 N

Drag to pan • wheel to zoom • tap either object to focus

Action–Reaction Lab

Explore paired forces in realistic interactions.

The forces are always equal

The two forces act on different objects, so they do not cancel each other.

Example case

Interaction force20 N

Mass of object A50 kg

Mass of object B70 kg

Contact duration1.0 s

Simulation speed1×

Zoom100%

Force on A20 N left

Force on B20 N right

Acceleration A

Acceleration B

Paired-force historyequal above/below zero

Focused objectObject A

What the law means

If object A pushes object B, object B simultaneously pushes object A with an equal force in the opposite direction. The pair is one interaction.

Important distinction

Action and reaction forces never cancel each other because they act on different objects. Forces cancel only when opposite forces act on the same object.

Multiple examples

Skaters: each pushes the other; the lighter skater accelerates more.
Rocket: rocket pushes exhaust backward; exhaust pushes rocket forward.
Balloon: balloon pushes air out; air pushes balloon ahead.
Boat: paddle pushes water backward; water pushes boat forward.
Walking: foot pushes ground backward; ground pushes the person forward.

Suggested experiments

Change one mass: forces stay equal but accelerations change.
Double interaction force: both force arrows double.
Compare all five examples and identify the two objects.
Pause during contact and track each object.

Score0 / 7