Skip to content
Open Model LabInteractive concept
HomeConcept libraryPhysicsMechanics
PhysicsMechanicsIntro

Concept module

Collisions

Collide two carts on one honest track, keep total momentum in view, and see how elasticity, mass, and incoming speed shape the rebound or stick-together outcome.

Interactive lab

Loading the live simulation bench.

Progress

Not startedMastery: NewLocal-first

Start exploring and Open Model Lab will keep this concept's progress on this browser first. No finished quick test, solved challenge, or completion mark is saved yet.

Let the live model runChange one real controlOpen What to notice

Try this setup

Jump to a named bench state or copy the one you are looking at now. Shared links reopen the same controls, graph, overlays, and compare context.

Saved setups

Premium keeps named exact-state study setups in your account while stable concept links stay public below.

Checking saved setup access.

This concept can keep using stable links while the saved-setups capability resolves for this browser.

Copy current setup

Stable concept and section links stay public below while exact-state setup sharing stays behind premium.

Stable links

Why it behaves this way

Explanation

A collision is a short interaction, but it does not erase the momentum story. If the two-cart system is isolated, then the total momentum before contact must match the total momentum after contact even when the individual cart velocities change abruptly.

This module keeps the setup bounded and honest with two carts on one fixed track, one contact point, and one elasticity control. You can change the masses and incoming speeds, then compare an elastic rebound with a more inelastic outcome without turning the page into a giant sandbox.

Key ideas

01Momentum conservation belongs to the whole two-cart system, so the total momentum line stays flat through contact.
02Elasticity tells you how much of the closing speed comes back as separation speed. Elastic collisions keep kinetic energy, while inelastic ones lose some kinetic energy even though momentum is still conserved.
03The same momentum rule can give very different post-collision speeds because mass changes how a given momentum change affects velocity.

Frozen walkthrough

Step through the frozen example

Frozen walkthrough
Solve the collision you are actually watching. The total-momentum check follows the current inspected moment, while the outcome check uses the current masses, incoming speeds, and elasticity to predict the post-collision velocities.

Premium unlocks saved study tools, exact-state sharing, and the richer review surfaces that support this guided flow.

View plans
Frozen valuesFrozen at 0.00

At , what is the system's total momentum?

Mass of A

1.2 kg

Velocity of A

1.6 m/s

Mass of B

2.2 kg

Velocity of B

-0.7 m/s

1. Add the cart momenta

Use for the same instant shown on the stage.

2. Substitute the live values

.

3. Compute the total

So .

Current total momentum

Before contact, the system total is already fixed by the incoming masses and velocities, so the collision has not created a new total.

Collision outcome checkpoint

Can you make cart A bounce backward while the system total momentum still points to the right?

Make a prediction before you reveal the next step.

Try a light cart A hitting a heavier cart B with a fairly elastic rebound. Predict whether the heavy cart can carry enough rightward momentum to keep the total positive.

Check your reasoning against the live bench.

Yes. Cart A can reverse while the total momentum stays rightward if cart B leaves the collision with enough positive momentum.
Momentum conservation constrains the sum, not the direction of each object. A light cart can rebound left after contact while the heavier cart keeps the system total moving right.

Common misconception

If momentum is conserved, then the carts must keep the same total kinetic energy and rebound the same way every time.

Momentum conservation does not guarantee kinetic-energy conservation. Inelastic collisions can keep the same total momentum while the total kinetic energy drops.

Mass and incoming velocity still matter. A light cart hitting a heavy one can rebound sharply, while a heavy cart can keep moving forward with only a modest speed change.

Quick test

Reasoning

Question 1 of 4

Use the stage and the linked graphs together. These checks are about reasoning through collisions, not just repeating the word conservation.

Which quantity must stay the same for this isolated two-cart collision system?

Use the live bench to test the result before moving on.

Accessibility

The simulation shows two carts moving on a fixed horizontal track toward one collision point. Each cart has a mass label and a horizontal velocity arrow, and optional overlays can mark the collision zone, the center of mass, the momentum bars, and the relative speed before or after contact.

Changing mass, incoming speed, or elasticity updates the same stage, readouts, and linked graphs without changing the track scale. A perfectly inelastic collision shows the carts leaving together, while higher elasticity shows them separating more strongly after contact.

Graph summary

The velocity graph shows the cart velocities changing at contact and includes a steady center-of-mass velocity line. The momentum graph shows the cart momentum lines changing while the total momentum line stays flat.

The energy graph shows when total kinetic energy is preserved and when it drops at contact, which is the main visual difference between elastic and inelastic behavior in this module.