Quick answer
This momentum calculator uses p = mv to find momentum, mass or velocity. Momentum measures how hard a moving object is to stop. Pick the quantity you need, enter the other two, and see the result with working.
Momentum (p = mv) calculator
How to Use the Momentum Calculator
- Choose momentum, mass or velocity.
- Enter the two known values: mass in kg, velocity in m/s or momentum in kg·m/s.
- Press Calculate.
Tip: To convert km/h into m/s, divide by 3.6. A car at 72 km/h is moving at 20 m/s.
Momentum Formula
p = mv
p is momentum in kg·m/s, m is mass in kg and v is velocity in m/s. Momentum is a vector, so it has the same direction as the velocity.
In a closed system the total momentum stays constant. That rule, the conservation of momentum, is explained with collision examples in our classical mechanics guide.
Worked Example
Worked example: a moving car
Question: A 1,200 kg car travels at 15 m/s. What is its momentum?
- Choose “Momentum (p)”.
- p = m × v = 1,200 × 15.
- p = 18,000 kg·m/s.
Answer: The car has a momentum of 18,000 kg·m/s (1.8 × 10⁴ kg·m/s) in its direction of travel.
Momentum and Impulse
A force acting for a time changes momentum. This change is called impulse: J = FΔt = Δp. Airbags, helmets and crumple zones all work by making Δt longer, which lowers the force for the same change in momentum.
Learn more: explore angular momentum and its conservation with real-world examples.
Frequently Asked Questions
What is the unit of momentum?
The SI unit of momentum is the kilogram metre per second (kg·m/s), which is the same as a newton second (N·s).
Is momentum a vector or scalar?
Momentum is a vector. It has both size and direction, and its direction is the same as the velocity.
Can momentum be negative?
Yes. A negative momentum simply means the object is moving in the direction you chose as negative.