Momentum Calculator

How to use the Momentum Calculator

1. 1Enter the mass, the velocity and, if you want the force, the time.
2. 2Pick the units or options from the menus if the momentum tool offers them.
3. 3Read the momentum in the large result box.
4. 4Look at the extra rows for related figures.
5. 5Press Copy result to keep the answer.

When you need the momentum

Momentum is the core idea behind collisions. Car safety engineers design crumple zones to make the stopping time longer, because a longer time at the same momentum means a smaller force. Sports coaches use the same idea when they teach players to follow through or to absorb a catch.

Students use it to solve conservation of momentum problems, and writers use it to explain why a heavy slow object and a light fast one can hit with the same punch. The optional time box turns the tool into an impact force estimate.

How the momentum is worked out

Momentum = mass × velocity, in kilogram-metres per second. Average force = change in momentum ÷ time taken. A 1,500 kg car moving at 20 m/s has a momentum of 1,500 × 20 = 30,000 kg·m/s. If a crash stops it in 0.1 s, the average force is 30,000 ÷ 0.1 = 300,000 N, about 30 tonnes-force.

Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.

• Mass in kg or lb
• Velocity in m/s, km/h or mph
• Optional stopping time for average force

Mistakes to avoid with momentum

Momentum has a direction, so a velocity in the opposite direction gives a negative momentum. Enter a negative velocity if you need that. Another trap is to confuse momentum with energy: momentum grows with speed, energy grows with the square of speed.

On phone and computer

On a phone, type into the boxes one after another and read the momentum underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the momentum move. The momentum calculator works the same on both. Momentum is linked to force and energy. Force Calculator shows the push that changes it, Kinetic Energy Calculator shows the energy, Speed Calculator finds the velocity, and Energy Converter changes the units.

Features

• Longer stop, smaller force
• Negative velocity means the other direction
• Not the same as energy
• Clear messages when the momentum inputs make no sense
• Copy the result with one tap
• Private: nothing is uploaded

Frequently asked questions