Momentum Calculator
Calculate momentum, mass, or velocity using the physics formula p = mv
Supports 1D linear momentum and 2D/3D vector momentum calculations
1D Momentum
Calculate momentum using the formula: p = m × v
What is Momentum?
Linear momentum (or simply "momentum") is the product of an object's mass and its velocity. Think of it as the "oomph" behind something in motion — the reason a bowling ball rolling at 10 mph feels very different from a ping-pong ball at the same speed.
🎯 Quick intuition: Momentum tells you how hard it is to stop something. A heavier object moving at the same speed has more momentum. A faster object of the same mass also has more momentum.
This calculator helps you work with momentum in 1D mode (motion along a single line) or 2D/3D mode (motion with components in multiple directions). Whether you're a physics student solving textbook problems or an engineer analyzing collisions, you'll find this tool handy.
📏 Units
SI units: kg·m/s or N·s (Newton-seconds). Imperial: lb·ft/s or slug·ft/s.
↗️ Vector Quantity
Momentum has both magnitude and direction — it points in the same direction as velocity.
⚖️ Conservation
In a closed system with no external forces, total momentum is conserved.
How to Use This Calculator
Our momentum calculator works bi-directionally — enter any two values, and it automatically calculates the third. Here's a quick walkthrough:
🔵 1D Momentum Mode
Choose 1D Momentum tab
Perfect for motion along a straight line.
Enter two known values
Example: Mass = 10 kg, Velocity = 5 m/s
Read the result
The third value appears automatically (highlighted in blue): Momentum = 50 N·s
🟣 2D/3D Momentum Mode
Switch to 2D/3D Momentum tab
Use this for projectile motion, collisions at angles, or 3D physics.
Enter mass and velocity components
Mass = 2 kg, vₓ = 3 m/s, vᵧ = 4 m/s
Get component-wise results
pₓ = 6 N·s, pᵧ = 8 N·s, |p| = 10 N·s
Fields highlighted in blue are calculated results. The calculator uses a "smart LRU" system — whichever field you edit least recently becomes the output.
Momentum Formula Explained
The momentum formula is beautifully simple — just mass times velocity:
Linear Momentum Equation
p = m × v
p = momentum (kg·m/s or N·s)
m = mass of the object (kg)
v = velocity of the object (m/s)
Rearranged forms:
- To find mass: m = p / v
- To find velocity: v = p / m
⚡ Connection to Newton's Second Law: Force equals the rate of change of momentum. In equation form: F = dp/dt. When mass is constant, this simplifies to the familiar F = ma.
Momentum in Two and Three Dimensions
Since momentum is a vector, it has components along each axis. If an object moves diagonally or in 3D space, you need to track each component separately:
Vector Momentum Components
pₓ = m × vₓ
pᵧ = m × vᵧ
p_z = m × v_z
Magnitude (total momentum)
|p| = √(pₓ² + pᵧ² + p_z²)
2D Example
A 5 kg ball moves with vₓ = 3 m/s, vᵧ = 4 m/s.
pₓ = 15 N·s, pᵧ = 20 N·s
|p| = √(225 + 400) = 25 N·s
Direction matters!
The momentum vector points in the same direction as velocity. This is crucial when analyzing collisions at angles.
If you're working with planar motion (like a projectile), just leave the Z component blank. The calculator handles 2D and 3D seamlessly.
Real-World Examples
Let's see momentum in action with some practical scenarios:
Jogger's Momentum
A person weighing 65 kg jogs at 2 m/s. What's their momentum?
p = 65 kg × 2 m/s = 130 N·s
To increase momentum to 195 N·s, they'd need to speed up to 3 m/s.
Dump Truck
An empty 12-ton dump truck travels at 35 mph.
p = 12,000 kg × 15.6 m/s ≈ 187,800 N·s
When fully loaded (24 tons), its momentum doubles — which is why braking distance increases significantly!
Charging Elephant
An elephant (5,000 kg) charging at 35 km/h (9.7 m/s).
p = 5,000 kg × 9.7 m/s ≈ 48,500 N·s
35 km/h doesn't sound fast, but combined with massive weight, that's some serious momentum. Definitely get out of the way!
Baseball in Flight (2D)
A 0.145 kg baseball with vₓ = 30 m/s, vᵧ = 20 m/s.
pₓ = 0.145 × 30 = 4.35 N·s
pᵧ = 0.145 × 20 = 2.9 N·s
|p| = √(4.35² + 2.9²) ≈ 5.23 N·s
Why Momentum Matters
Momentum isn't just an abstract physics concept — it has profound practical implications:
Braking & Safety
A truck's momentum determines how much force (brakes) over what time is needed to stop. Higher momentum = longer stopping distance.
Collision Analysis
Crash investigators use momentum conservation to reconstruct accidents and determine pre-impact velocities.
Rocket Propulsion
Rockets work by conservation of momentum — ejecting mass at high velocity creates an equal and opposite momentum change.
Sports Physics
From baseball bats to golf clubs, understanding momentum transfer helps optimize equipment and technique.
🔬 Conservation Law: In any closed system (no external forces), total momentum before = total momentum after. This is one of the most powerful principles in physics!
Large forces acting over short times (like a ball hitting a wall) create impulse, which equals the change in momentum. Interested in impact forces? Impulse calculators can help with that analysis.
Tips & Best Practices
The calculator handles unit conversions automatically, but make sure you're using the same unit system throughout your problem for clarity.
Common mistakes to avoid
- •Forgetting that momentum is a vector — direction matters in 2D/3D!
- •Confusing mass units (grams vs kilograms can give answers off by 1000×)
- •Using speed instead of velocity (velocity has direction, speed doesn't)
- •Entering negative velocity when you mean to indicate direction — use components in 2D/3D mode instead
🎓 Study tip: When solving collision problems, always set up a coordinate system first. Define positive direction, then use conservation of momentum: m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'
🔄 Sign conventions
In 1D, positive/negative velocity indicates direction. In 2D/3D, use component signs (e.g., vₓ = -5 means moving left).
📊 Sanity checks
Momentum should be proportional to both mass and velocity. If doubling mass doesn't double momentum, check your inputs!
Frequently Asked Questions
What's the difference between momentum and kinetic energy?
Momentum (p = mv) is a vector and conserved in collisions. Kinetic energy (KE = ½mv²) is a scalar and may not be conserved (think inelastic collisions). They measure different things!
Can momentum be negative?
Yes! Negative momentum simply indicates direction. If you define rightward as positive, then leftward motion gives negative momentum. It's all about your chosen coordinate system.
Why is momentum conserved?
It stems from Newton's third law — every action has an equal and opposite reaction. In a closed system, internal forces cancel out, so total momentum stays constant.
What units should I use?
SI units (kg, m/s, N·s) are standard in physics. The calculator supports multiple units and converts automatically. Just be consistent within your problem.
How do I calculate momentum for rotating objects?
That's angular momentum (L = Iω), which is different from linear momentum. This calculator handles linear motion only. For rotation, you'd need an angular momentum calculator.
What happens to momentum in a perfectly inelastic collision?
Momentum is still conserved! The objects stick together and move with a common velocity. Energy is lost to deformation/heat, but momentum conservation holds.
How accurate is this calculator?
The math is exact (p = mv is straightforward). We use high-precision arithmetic internally and preserve accuracy across unit conversions. Results are displayed to 10 significant figures.
Can I share my calculation?
Absolutely! Click the Share button and check "Include results" to generate a link with all your inputs. Perfect for collaborating on physics homework.
Limitations & Sources
- •This calculator assumes classical mechanics (non-relativistic). For objects near light speed, relativistic momentum applies.
- •Only linear momentum is calculated here. For rotational systems, angular momentum is needed.
- •Results are for educational purposes. For engineering applications, verify with professional tools and safety factors.
- •The calculator treats mass as constant. For systems with changing mass (rockets, etc.), more complex equations apply.
External References & Further Reading
- •Khan Academy: Linear Momentum and Collisions
- •The Physics Classroom: Momentum
- •OpenStax University Physics: Linear Momentum
These resources provide excellent supplementary material for understanding momentum concepts in greater depth.
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