![]() There are a few things that impact the physics behind g-force, and how strong or severe it is in a collision. If you’ve ever been in a car collision, had to do an emergency stop, or even just had to slam the brakes on quickly, you’ll have experienced first-hand the effect that G-force can have on passengers in a vehicle. That feeling of “pulled” or jolted forward as the vehicle around you stops can actually have a huge impact on the severity of a collision or crash in any vehicle. When you’re driving, you and your vehicle possess kinetic energy and when you stop suddenly, this energy has nowhere to go! This is when you’ll experience g-force. This is a delicate balancing act, due to the impact of g-force on vehicle drivers and passengers. One of the most important jobs of crash barriers is to stop vehicles from moving as quickly and safely as possible. With the chosen coordinate system, p yis initially zero and p xis the momentum of the incoming particle.Safety Science & the Physics of a Collision Because momentum is conserved, the components of momentum along the x- and y-axes, displayed as p xand p y, will also be conserved. The best choice for a coordinate system is one with an axis parallel to the velocity of the incoming particle, as shown in Figure 8.8. The simplest collision is one in which one of the particles is initially at rest. We start by assuming that F net = 0, so that momentum p is conserved. To avoid rotation, we consider only the scattering of point masses-that is, structureless particles that cannot rotate or spin. We will not consider such rotation until later, and so for now, we arrange things so that no rotation is possible. For example, if two ice skaters hook arms as they pass each other, they will spin in circles. One complication with two-dimensional collisions is that the objects might rotate before or after their collision. But what about collisions, such as those between billiard balls, in which objects scatter to the side? These are two-dimensional collisions, and just as we did with two-dimensional forces, we will solve these problems by first choosing a coordinate system and separating the motion into its x and y components. In one-dimensional collisions, the incoming and outgoing velocities are all along the same line. The Khan Academy videos referenced in this section show examples of elastic and inelastic collisions in one dimension. Some of the energy of motion gets converted to thermal energy, or heat. The two objects come to rest after sticking together, conserving momentum but not kinetic energy after they collide. Two objects that have equal masses head toward each other at equal speeds and then stick together. Figure 8.7 shows an example of an inelastic collision. For inelastic collisions, kinetic energy may be lost in the form of heat. The concepts of energy are discussed more thoroughly elsewhere. This lack of conservation means that the forces between colliding objects may convert kinetic energy to other forms of energy, such as potential energy or thermal energy. An inelastic collision is one in which objects stick together after impact, and kinetic energy is not conserved. Now, let us turn to the second type of collision. The magnitudes of a →, b →, and r → are A, B, and R, respectively. The resultant vector of the addition of vectors a → and b → is r →.
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