What are the units of momentum?
kg·m/s, which equals N·s. Both are correct SI units.
Momentum Calculator
p = mv
Calculate momentum from mass and velocity. p = mv — the product of mass and velocity, conserved in all isolated systems.
Calculate
Enter values above to calculate
How it calculates
1
Read mass m in kg and velocity v in m/s
2
Multiply: p = m × v
3
Result is in kg·m/s (= N·s)
Formula
p = mv
Variable Table
| Symbol | Quantity | SI Unit |
|---|---|---|
| p | Linear momentum | kg·m/s |
| m | Mass | kg |
| v | Velocity | m/s |
→ Read the full Momentum article
How to Use This Calculator
This momentum calculator is built for quick physics checks and worked-problem review. Enter values in the units shown beside each input, then compare the result with the formula and variable table before using it in a longer solution. The calculator does the arithmetic, but the physics still depends on choosing a model that matches the situation.
Start by identifying the system, the known quantities, and the quantity you want to find. If a value is given in a non-SI unit, convert it before substitution. A correct numerical answer with mixed units can still be physically wrong, especially when squared units, inverse seconds, charges, temperatures, or distances are involved.
Assumptions and Limits
The formula p = mv is a model, not a universal description of every possible case. It assumes the quantities in the variable table are the relevant quantities for the problem and that hidden effects are either negligible or already included in the inputs. If friction, drag, relativistic speeds, changing fields, non-constant temperature, or geometry-specific effects matter, check whether a more complete model is needed.
Use the result as a magnitude and units check. Ask whether the answer has the right sign, whether it grows or shrinks when an input changes, and whether the limiting cases make sense. Setting an input to zero, doubling a quantity, or using a very large value is often enough to catch a formula choice or unit mistake before it reaches a final answer.
Worked Example
A 0.15 kg cricket ball moves at 40 m/s. Find its momentum.
Step 1: p = m × v
Step 2: p = 0.15 × 40
Answer: p = 6 kg·m/s
Common Mistakes
- Momentum is a vector — direction matters in 2D problems
- Do not confuse p (momentum) with P (pressure or power)
- Ensure velocity is in m/s before substituting
Related
Frequently Asked Questions
Is momentum always conserved?
In any system with no net external force, total momentum is conserved — regardless of collisions or internal forces.