Mathematically this can be expressed as:. To change momentum of a body we need to change its velocity or its mass. In sport and physical exercise there are mostly no changes in the mass of a human body, therefore a change to momentum is caused almost exclusively by changes to velocity.
Resultant external force acting on a human body for certain time causes changes to its momentum. To cause greater change to momentum we have to either use greater force for the same period of time, or the same force for a longer period of time.
In many sports the elementary motor task is to change as much as possible the velocity of human body, its parts, or of an object. In throwing, kicking, tossing, and jumping the projectiles at the beginning of their motion have zero velocity. When fulfilling a motor task, for example throwing javelin, we are trying to give the javelin at the end of our motion the greatest possible velocity.
We are therefore trying to increase the momentum of the javelin. The same follows for certain strokes in tennis, boxing and other sports. In these unexpected cases, the collision between wall and egg lasts for a short period of time, thus maximizing the effect of the force on the egg. The egg brakes and leaves the wall and floor in a considerable mess. And that's no yolk! Occasionally when objects collide, they bounce off each other as opposed to sticking to each other and traveling with the same speed after the collision.
Bouncing off each other is known as rebounding. Rebounding involves a change in the direction of an object; the before- and after-collision direction is different. Rebounding was pictured and discussed earlier in Lesson 1. At that time, it was said that rebounding situations are characterized by a large velocity change and a large momentum change. From the impulse-momentum change theorem, we could deduce that a rebounding situation must also be accompanied by a large impulse.
Since the impulse experienced by an object equals the momentum change of the object, a collision characterized by a large momentum change must also be characterized by a large impulse. The importance of rebounding is critical to the outcome of automobile accidents. In an automobile accident, two cars can either collide and bounce off each other or collide, crumple up and travel together with the same speed after the collision. But which would be more damaging to the occupants of the automobiles - the rebounding of the cars or the crumpling up of the cars?
Contrary to popular opinion, the crumpling up of cars is the safest type of automobile collision. As mentioned above, if cars rebound upon collision, the momentum change will be larger and so will the impulse.
A greater impulse will typically be associated with a bigger force. Occupants of automobiles would certainly prefer small forces upon their bodies during collisions. In fact, automobile designers and safety engineers have found ways to reduce the harm done to occupants of automobiles by designing cars that crumple upon impact. Automobiles are made with crumple zones. Crumple zones are sections in cars that are designed to crumple up when the car encounters a collision.
Crumple zones minimize the effect of the force in an automobile collision in two ways. By crumpling, the car is less likely to rebound upon impact, thus minimizing the momentum change and the impulse.
Finally, the crumpling of the car lengthens the time over which the car's momentum is changed; by increasing the time of the collision, the force of the collision is greatly reduced. Physics Tutorial. My Cart Subscription Selection. Student Extras. We Would Like to Suggest Sometimes it isn't enough to just read about it.
You have to interact with it! And that's exactly what you do when you use one of The Physics Classroom's Interactives. We would like to suggest that you combine the reading of this page with the use of our Egg Drop Interactive.
You can find it in the Physics Interactives section of our website. The Egg Drop Interactive immerses a learner into a Virtual Egg Drop activity in order to explore the effect of drop height, egg mass, and landing surface upon the outcome of the egg. Visit: Egg Drop Interactive. Consider the interaction between a large cannon and the cannonball that it fires. During the explosion, which object experiences the greatest:.
Cannon Cannonball Both the same. Sanders' Site. Momentum and Impulse Connection Newton's second law : an unbalanced force always accelerates an object - either speeding it up or slowing it down. Real-World Applications The greater the time over which the collision occurs, the smaller the force acting upon the object. During the explosion, which object experiences the greatest: force F? Cannon Cannonball Both the same time duration t of the force?
Cannon Cannonball Both the same velocity change? Cannon Cannonball Both the same acceleration a? My Resources. Classroom News. My Homework. My Calendar. Kinematic Equations.
Newtons 3rd Law. Notes on Acceleration Graphs. Notes on Forces. Notes on Newtons 1st Law. Notes on Newtons 2nd Law. Notes on Vectors. Notes on Velocity Graphs. Types of Forces. Notes on Inclined Planes. Projectile Motion Notes. Notes on Momentum and Impulse. Circular Motion. Universal Law of Gravitation. Energy in a Closed System. Notes on Springs.
0コメント