Try the law in 3 steps
1. Push the cart 2. Release the force
3. With net force = 0, watch velocity remain constant.

Zero net force: remains at rest

Drag to pan • wheel or pinch to zoom • tap the cart, arrows, or track

Inertia & Motion Lab

Explore Newton's first law using a low-friction dynamics track.

Balanced forces: inertia preserves velocity

No net force means no acceleration. A stationary cart remains stationary until an unbalanced force acts.

Mode

Applied force 0 N

Friction 0.00

Cart mass 2.0 kg

Initial velocity 0.0 m/s

Simulation speed 1×

Zoom 100%

Focused object Cart

Net force 0.0 N

Acceleration 0.0 m/s²

Velocity 0.0 m/s

Motion state At rest

Velocity history m/s

Teacher / Demo tools

Laser annotation

The law of inertia

An object's velocity changes only when a nonzero net external force acts. Rest and constant straight-line motion are both examples of unchanged velocity.

Force and motion are different

Force causes acceleration, not velocity.
Balanced forces produce zero acceleration.
A moving object does not need a continuous force to keep moving.
Friction often hides inertia by slowing everyday objects.
Greater mass means greater resistance to acceleration.

Learning objectives

Connect zero net force with constant velocity.
Distinguish velocity, acceleration, applied force, and net force.
Explain why friction makes moving objects stop.
Predict how mass affects response to the same force.
Identify inertia in vehicles, sports, and spaceflight.

Suggested experiments

Push the cart briefly and then release the force.
Observe the flat velocity graph when friction is zero.
Add friction and identify the force that stops the cart.
Compare light and heavy carts under the same push.

Questions for exploration

Why do passengers move forward when a bus suddenly stops? Why does a hockey puck travel farther on ice than on carpet? Does a spacecraft need continuous thrust to coast?

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