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Impulsive force physics7/21/2023 ![]() ![]() 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. The flyby thus can be modeled to some extent as impulsive.You can see from the equation that momentum is directly proportional to the object’s mass ( m) and velocity ( v). The period of time over which the planet had a significant effect on the satellite is short compared to the orbital period of the planet. During the flyby, the gravitational force exerted by the planet on the satellite is several orders of magnitude large than the gravitational force exerted by the Sun on the satellite. ![]() Most of NASA's deep space missions take advantage of gravity assists. Suppose the satellite comes close to but does not impact the planet, and then moves on. Imagine a satellite moving toward a planet. ![]() That said, there is a place where gravitation can be treated as impulsive. Gravitation is a small force whose effects only becomes significant when applied over long periods of time. Modeling a force as impulsive is approximately valid when that dominates over all other forces and when that dominant force is only applied for a short period of time. People model forces as impulsive because doing so can make analysis much simpler. It's important to note that there is no such thing as an impulsive force, a force that instantaneously change momentum. Gravitation was negligible during the immediate contact. That's about four orders of magnitude smaller than the impact force. The gravitational force at the time of impact was about 2×10 16 newtons, directed downward. A force that large exerted over that a short of a period of time qualifies as "impulsive". The force needed to stop a 2 teraton object moving at 20 km/s is about 4×10 20 newtons, directed against the velocity vector. The collision stopped that impactor in about one tenth of a second. A number of other forces that completely overwhelm gravity are involved in a collision of heavenly bodies other than gravity.Ĭonsider the Chicxulub impactor, a roughly 2 teraton object that collided with the Earth at about 20 km/s. While gravity may have drawn the objects together, it plays a trivial role during the actual collision. When two heavenly objects collide then the force exerted on each of them during the time of impact is due to gravity, hence can it be termed as impulsive? Yes, but not in the circumstance you described. ![]() Can gravitational force be termed as impulsive in any case? ![]()
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