Mechanics - Momentum - Impulse and the change in momentum - Page 4
A crumple zone, seatbelt, and airbag slows down the car so that the force is smaller, thus making them Interested in Impulse and Momentum in Collisions?. Momentum · Momentum and Impulse Connection; Real-World Applications This is known as the impulse-momentum change theorem. Air bags are used in automobiles because they are able to minimize the effect of the force on an object. This lower number for net velocity as compared to particle velocity will always There is, in fact, a relationship between impulse, momentum change, transfer of A crumple zone—and there are usually several in a single automobile—is a.
There is, in fact, a relationship between impulse, momentum change, transfer of kinetic energy, and the impact—desirable or undesirable—experienced as a result. Impulse, again, is equal to momentum change—and also equal to force multiplied by time interval or change in time.
This means that the greater the force and the greater the amount of time over which it is applied, the greater the momentum change.
Even more interesting is the fact that one can achieve the same momentum change with differing levels of force and time interval. In other words, a relatively low degree of force applied over a relatively long period of time would produce the same momentum change as a relatively high amount of force over a relatively short period of time. The conservation of kinetic energy in a collision is, as noted earlier, a function of the relative elasticity of that collision.
The question of whether KE is transferred has nothing to do with impulse.
On the other hand, the question of how KE is transferred—or, even more specifically, the interval over which the transfer takes place—is very much related to impulse. Ifa moving car were to hit a stationary car head-on, it would transfer a quantity of kinetic energy to the stationary car equal to one-half its own mass multiplied by the square of its velocity.
This, of course, assumes that the collision is perfectly elastic, and that the mass of the cars is exactly equal. A transfer of KE would also occur if two moving cars hit one another head-on, especially in a highly elastic collision. Assuming one car had considerably greater mass and velocity than the other, a high degree of kinetic energy would be transferred—which could have deadly consequences for the people in the car with less mass and velocity. Even with cars of equal mass, however, a high rate of acceleration can bring about a potentially lethal degree of force.
In a highly elastic car crash, two automobiles would bounce or rebound off one another. This would mean a dramatic change in direction—a reversal, in fact—hence, a sudden change in velocity and therefore momentum.
On the other hand, it is possible to have a highly inelastic car crash, accompanied by a small change in momentum. It may seem logical to think that, in a crash situation, it would be better for two cars to bounce off one another than for them to crumple together.
In fact, however, the latter option is preferable. When the cars crumple rather than rebounding, they do not experience a reversal in direction. They do experience a change in speed, of course, but the momentum change is far less than it would be if they rebounded.
Furthermore, crumpling lengthens the amount of time during which the change in velocity occurs, and thus reduces impulse.
But even with the reduced impulse of this momentum change, it is possible to further reduce the effect of force, another aspect of impact. For this reason, car manufacturers actually design and build into their cars a feature known as a crumple zone. A crumple zone—and there are usually several in a single automobile—is a section in which the materials are put together in such a way as to ensure that they will crumple when the car experiences a collision.
Of course, the entire car cannot be one big crumple zone—this would be fatal for the driver and riders; however, the incorporation of crumple zones at key points can greatly reduce the effect of the force a car and its occupants must endure in a crash. Another major reason for crumple zones is to keep the passenger compartment of the car intact.
Real-life applications - Momentum - When Two Objects Collide, Two lumps of clay
Many injuries are caused when the body of the car intrudes on the space of the occupants—as, for instance, when the floor buckles, or when the dashboard is pushed deep into the passenger compartment.
Obviously, it is preferable to avoid this by allowing the fender to collapse. An airbag is another way of minimizing force in a car accident, in this case by reducing the time over which the occupants move forward toward the dashboard or wind-shield. The airbag rapidly inflates, and just as rapidly begins to deflate, within the split-second that separates the car's collision and a person's collision with part of the car. As it deflates, it is receding toward the dashboard even as the driver's or passenger's body is being hurled toward the dashboard.
It slows down impact, extending the amount of time during which the force is distributed. By the same token, a skydiver or paratrooper does not hit the ground with legs outstretched: Rather, as a parachutist prepares to land, he or she keeps knees bent, and upon impact immediately rolls over to the side.
Thus, instead of experiencing the force of impact over a short period of time, the parachutist lengthens the amount of time that force is experienced, which reduces its effects. The same principle applies if one were catching a water balloon.
In order to keep it from bursting, one needs to catch the balloon in midair, then bring it to a stop slowly by "traveling" with it for a few feet before reducing its momentum down to zero.
Once again, there is no way around the fact that one is attempting to bring about a substantial momentum change—a change equal in value to the momentum of the object in movement. Nonetheless, by increasing the time component of impulse, one reduces the effects of force.
In old Superman comics, the "Man of Steel" often caught unfortunate people who had fallen, or been pushed, out of tall buildings. The cartoons usually showed him, at a stationary position in midair, catching the person before he or she could hit the ground. In fact, this would not save their lives: Of course, it is a bit absurd to quibble over scientific accuracy in Superman, but in order to make the situation more plausible, the "Man of Steel" should have been shown catching the person, then slowly following through on the trajectory of the fall toward earth.
But what if—to once again turn the tables—a strong force is desired? This time, rather than two pool balls striking one another, consider what happens when a batter hits a baseball. Once more, the correlation between momentum change and impulse can create an advantage, if used properly.Understanding Car Crashes - Momentum
In order to hit a line drive or "knock the ball out of the park," the batter must therefore cause a significant change in momentum. Consider the momentum change in terms of the impulse components. The batter can only apply so much force, but it is possible to magnify impulse greatly by increasing the amount of time over which the force is delivered. Air bags are used in automobiles because they are able to minimize the effect of the force on an object involved in a collision.
Air bags accomplish this by extending the time required to stop the momentum of the driver and passenger. When encountering a car collision, the driver and passenger tend to keep moving in accord with Newton's first law.
Their motion carries them towards a windshield that results in a large force exerted over a short time in order to stop their momentum. If instead of hitting the windshield, the driver and passenger hit an air bag, then the time duration of the impact is increased.
When hitting an object with some give such as an air bag, the time duration might be increased by a factor of Increasing the time by a factor of will result in a decrease in force by a factor of Now that's physics in action. The same principle explains why dashboards are padded. If the air bags do not deploy or are not installed in a carthen the driver and passengers run the risk of stopping their momentum by means of a collision with the windshield or the dashboard.
If the driver or passenger should hit the dashboard, then the force and time required to stop their momentum is exerted by the dashboard. Padded dashboards provide some give in such a collision and serve to extend the time duration of the impact, thus minimizing the effect of the force. This same principle of padding a potential impact area can be observed in gymnasiums underneath the basketball hoopsin pole-vaulting pits, in baseball gloves and goalie mitts, on the fist of a boxer, inside the helmet of a football player, and on gymnastic mats.
Fans of boxing frequently observe this same principle of minimizing the effect of a force by extending the time of collision. When a boxer recognizes that he will be hit in the head by his opponent, the boxer often relaxes his neck and allows his head to move backwards upon impact. In the boxing world, this is known as riding the punch. A boxer rides the punch in order to extend the time of impact of the glove with their head.
Extending the time results in decreasing the force and thus minimizing the effect of the force in the collision. Merely increasing the collision time by a factor of ten would result in a tenfold decrease in the force. Nylon ropes are used in the sport of rock-climbing for the same reason.
Rock climbers attach themselves to the steep cliffs by means of nylon ropes. If a rock climber should lose her grip on the rock, she will begin to fall.
In such a situation, her momentum will ultimately be halted by means of the rope, thus preventing a disastrous fall to the ground below. The ropes are made of nylon or similar material because of its ability to stretch. If the rope is capable of stretching upon being pulled taut by the falling climber's mass, then it will apply a force upon the climber over a longer time period. Extending the time over which the climber's momentum is broken results in reducing the force exerted on the falling climber.
For certain, the rock climber can appreciate minimizing the effect of the force through the use of a longer time of impact. In racket and bat sports, hitters are often encouraged to follow-through when striking a ball.
This increase in time must result in a change in some other variable in the impulse-momentum change theorem. Surprisingly, the variable that is dependent upon the time in such a situation is not the force.
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The force in hitting is dependent upon how hard the hitter swings the bat or racket, not the time of impact. Instead, the follow-through increases the time of collision and subsequently contributes to an increase in the velocity change of the ball. By following through, a hitter can hit the ball in such a way that it leaves the bat or racket with more velocity i. In tennis, baseball, racket ball, etc. You undoubtedly recall other illustrations of this principle.
A common physics demonstration involves the catching of water balloons of varying speed and varying mass. A water balloon is thrown high into the air and successfully caught i. The key to the success of the demonstration is to contact the balloon with outstretched arms and carry the balloon for a meter or more before finally stopping its momentum.
The effect of this strategy is to extend the time over which the collision occurred and so reduce the force. This same strategy is used by lacrosse players when catching the ball.