# Centre of mass impulse and momentum relationship

### Momentum and Impulse Connection

V. Momentum and kinetic energy in collisions. VI. The center of mass lies somewhere between the two particles. . Impulse-linear momentum theorem. Learn what momentum and impulse are, as well as how they are related to force. This simple relationship means that doubling either the mass or velocity of an. A better understanding of concept of Center of mass and Collisions for Plus one Again, no direct formula is helpful for such questions. any collision problem are conservation of energy and conservation of momentum.

In many real life problems involving impulse and momentum, the impulse acting on a body consists of a large force acting for a very short period of time — for example, a hammer strike, or a collision between two bodies. The following problem illustrates the principle of impulse and momentum. A solid ball of mass m and radius r is rolling without slipping on a flat horizontal surface, at an initial angular velocity w1. It hits a small bump of height h.

What is the angular velocity of the ball immediately after impact? Also, what is the minimum initial angular velocity w1 so that the ball just makes it over the bump? What is the minimum initial speed of the ball? Assume that the ball pivots about the tip of the bump during, and after impact. Solution Set up a schematic of this problem, as shown, along with sign convention. Assume the center of mass G is at the geometric center of the ball. Gravity g is pointing down.

During impact the ball is assumed to pivot about P, as indicated. Let Fpx be the horizontal impulse force at point P, and Fpy be the vertical impulse force at point P. We can treat this as a planar motion problem. It can be solved using the principle of impulse and momentum. Since this problem combines translation and rotation we must apply the equations for linear momentum and angular momentum.

In an impact of very short time duration say, between an initial time ti and a final time tfthe impact force Fimp is typically very large. This means that the impulse term given by is dominated by the impact force Fimp, since mg the gravitational force is much smaller than Fimp. Therefore, we can ignore gravity for the impulse calculation. For planar motion in the xy plane, the equations for impulse and linear momentum are: Since the ball initially rolls without slipping, The negative sign accounts for the fact that positive angular velocity means the ball rolls to the left in the negative x-direction.

### Outline - Center of Mass, Momentum, and Collisions - Physics

Since the ball initially rolls on a flat horizontal surface, Immediately after impact the ball pivots about point P on the tip of the bump with an angular velocity wf. As a result the velocity of the center of mass vGfafter impact, is perpendicular to the line joining point G to point P.

Since the ball pivots about point P immediately after impact: If the force acts opposite the object's motion, it slows the object down.

If a force acts in the same direction as the object's motion, then the force speeds the object up. Either way, a force will change the velocity of an object. And if the velocity of the object is changed, then the momentum of the object is changed. Impulse These concepts are merely an outgrowth of Newton's second law as discussed in an earlier unit. To truly understand the equation, it is important to understand its meaning in words.

In words, it could be said that the force times the time equals the mass times the change in velocity. The physics of collisions are governed by the laws of momentum; and the first law that we discuss in this unit is expressed in the above equation.

The equation is known as the impulse-momentum change equation. The law can be expressed this way: In a collision, an object experiences a force for a specific amount of time that results in a change in momentum. The result of the force acting for the given amount of time is that the object's mass either speeds up or slows down or changes direction.

## What are momentum and impulse?

The impulse experienced by the object equals the change in momentum of the object. In a collision, objects experience an impulse; the impulse causes and is equal to the change in momentum.

Consider a football halfback running down the football field and encountering a collision with a defensive back. The collision would change the halfback's speed and thus his momentum. If the motion was represented by a ticker tape diagramit might appear as follows: At approximately the tenth dot on the diagram, the collision occurs and lasts for a certain amount of time; in terms of dots, the collision lasts for a time equivalent to approximately nine dots. In the halfback-defensive back collision, the halfback experiences a force that lasts for a certain amount of time to change his momentum.

Since the collision causes the rightward-moving halfback to slow down, the force on the halfback must have been directed leftward. If the halfback experienced a force of N for 0.