By rearranging the equation for impulse to solve for force F net = Δ p Δ t, F net = Δ p Δ t, you can see how increasing Δ t Δ t while Δ p Δ p stays the same will decrease F net.

But the force that brings the occupant to a stop will be much less if it acts over a larger time. The momentum change is the same for an occupant whether an airbag is deployed or not. The change in momentum is the difference between the final and initial values of momentum.įigure 8.2 Vehicles have safety features like airbags and seat belts installed.Īirbags allow the net force on the occupants in the car to act over a much longer time when there is a sudden stop. Newton actually stated his second law of motion in terms of momentum: The net external force equals the change in momentum of a system divided by the time over which it changes. Recall our study of Newton’s second law of motion ( F net = m a). Force influences momentum, and we can rearrange Newton’s second law of motion to show the relationship between force and momentum. Momentum is so important for understanding motion that it was called the quantity of motion by physicists such as Newton.

Since mass is a scalar, when velocity is in a negative direction (i.e., opposite the direction of motion), the momentum will also be in a negative direction and when velocity is in a positive direction, momentum will likewise be in a positive direction. Momentum is a vector and has the same direction as velocity v. A large, fast-moving object has greater momentum than a smaller, slower object. Therefore, the greater an object’s mass or the greater its velocity, the greater its momentum. You can see from the equation that momentum is directly proportional to the object’s mass ( m) and velocity ( v).

Impulse and impulsive force