How to use (3 steps)
- Pick a collision type: elastic (e = 1), perfectly inelastic (stick together), or inelastic with your own e.
- Enter masses and initial velocities u₁ and u₂. Use negative values to show the opposite direction on the 1D line.
- Press Compute to get v₁, v₂, momentum and energy before/after, then copy the URL to share the setup.
Default example: m₁ = 1 kg, u₁ = 3 m/s, m₂ = 2 kg, u₂ = 0 m/s, elastic. It auto-computes on load so you can see the result instantly.
Inputs
Use kg and m/s. This calculator keeps the sign of each velocity; rightward is positive by convention.
Results
How it's calculated
Using the 1D collision calculator
This calculator keeps the sign of velocity, so rightward motion can be positive and leftward motion can be negative. Decide that sign convention first, then keep it consistent for both objects.
Suggested workflow
- Choose the collision model that matches your lesson: elastic, perfectly inelastic, or a custom restitution value.
- Enter masses and signed initial velocities for both objects.
- Use the result and step list together to check momentum conservation and, when relevant, how kinetic energy changes.
What the page assumes
It is a one-dimensional model with no rotation, deformation details, or external forces during the impact interval. That makes it suitable for textbook mechanics and quick checks, not crash reconstruction.
Common mistakes to avoid
- Typing all speeds as positive even when one object moves in the opposite direction.
- Using an inelastic mode and then expecting kinetic energy to remain unchanged.
- Comparing final speeds only, without checking total momentum before and after the collision.
See also
FAQ
What is the difference between elastic and inelastic collisions?
Elastic collisions conserve both momentum and kinetic energy (e = 1). Inelastic collisions conserve momentum but lose some kinetic energy. In a perfectly inelastic collision the objects stick together and move with one final speed.
Can I enter negative speeds?
Yes. Set rightward as positive on the 1D line. A negative value means the object travels to the left, and the calculator keeps that sign when summing momentum.
What does the coefficient of restitution e mean?
It is the ratio of relative speed after impact to relative speed before impact. e = 1 is perfectly elastic, e = 0 is perfectly inelastic, and values between 0 and 1 describe partially elastic collisions.
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