What is the product of force and time called?

The product of force and time is called impulse. For a constant force, impulse is calculated as J = FΔt, where J is impulse, F is force, and Δt is the time interval.

Impulse measures how strongly a force changes an object's momentum. Because force and momentum are vectors, impulse has both magnitude and direction. A larger force, a longer contact time, or both produce a greater impulse. Its SI unit is the newton-second (N·s), which is equivalent to kilogram-metre per second (kg·m/s), the unit of momentum.

For a changing force, the product formula becomes the area under a force–time graph: J = ∫F dt. Newton's second law connects impulse to momentum through the impulse–momentum theorem, J = Δp. This is why airbags, helmets, and padded landing surfaces reduce injury: they increase the time over which a person's momentum changes, lowering the average force.

Impulse is often confused with momentum. Momentum describes an object's state of motion; impulse describes the change in that motion caused by a force.