When to use this calculator
Find relative speed between two objects moving along the same line. Use signs to represent direction on one common straight axis.
Explore the motion & kinematics calculators for other questions in this topic. For a related calculation, use the Rotational Period Calculator: Find time per full rotation from a rotational speed.
PUTTING IT INTO PRACTICE
Relative Speed: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| First signed velocity (m/s) | 20 |
| Second signed velocity (m/s) | -10 |
| Result | 30 m/s |
- Check the input labels and enter the example values above.
- Apply the relationship: Relative speed = |velocity one − velocity two|.
- The result is 30 m/s, rounded for display.
How to interpret your result
Use signs to represent direction on one common straight axis.
Choose a reference direction before using signed velocities. Constant-acceleration models do not capture variable braking or drag. Projectile tools explicitly state launch and landing assumptions.
Frequently asked questions
Are displacement and distance interchangeable?
No. Displacement is the signed or directed change in position; distance counts the length of the path travelled.
When is the relative speed calculator useful?
Find relative speed between two objects moving along the same line. Use signs to represent direction on one common straight axis.
How do I use the relative speed calculator?
Enter first signed velocity (m/s), second signed velocity (m/s). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Relative speed = |velocity one − velocity two|.
What should I check before using the result?
Use signs to represent direction on one common straight axis.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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