PhyUnit7

Momentum and Impulse

Net forces cause objects to accelerate and the acceleration is dependent upon the size of the force and inversely proportional to the mass of the object. To fully understand the impact of a force acting on an object we need a new concept.

Momentum is the product of an objects mass and velocity. This considers not only how large an object is but how fast it is moving as well. Since velocity is one component it is a vector quantity as well. Momentum uses the greek symbol rho or an italicised p, so rho = mV or p = mV. The units associated with momentum are kg *m/s.

Newtons first law declares that when no net force acts on an object it will move at a constant velocity, even if that velocity is zero. Since mass is a constant, this means that when no net forces act on an object, the objects velocity and thus momentum are constant. This explains the Law of Conservation of Momentum which says that in a closed system, momentum is conserved unless an outside force acts on the system.

Newtons second law, F = m/a can be rewritten to substitute the equation for acceleration into the equation so F = m /\v/t .

If we solve for m/\v we have the change in momentum. Rearranging the equation above we find that F/\t = m/\v.

This means a change in momentum is caused by a force that acts on an object for some duration of time. This force over time is called an impulse. An impulse causes momentum to change so we can say that impulse equals a change in momentum which is the equation above . This is the root of the Impulse-Momentum theory which declares that a net force acting on an object for a time will cause a change in momentum.

This is the principle behind airbags. By slowing down the deceleration or impact time it reduces the force the body experiences.

All momentum is conserved, whether it is linear momentum or circular (angular) momentum. Angular momentum depends upon a force acting over some time plus the distance the force acts from the center of rotation. So basically angular momentum depends upon torque and the time the torque is acting. Remember Kepler's Laws of Planetary Motion? Basically since the force of attraction varies it conserves angular momentum.

This conservation of momentum is true only within a closed system. By system we mean a specified collection of objects under consideration. In a closed system, no objects enter or leave the system.

Internal forces may alter the individual momentum of objects but the system momentum will remain unchanged. Only an external force can alter the total momentum.

To calculate individual changes in momentum we set the initial and final momentum equal to each other or the loss of momentum of one equals the gain in momemtum of the other.

m1V1 = m2V2

This page was last updated on: November 6, 2001



	Momentum and Impulse Net forces cause objects to accelerate and the acceleration is dependent upon the size of the force and inversely proportional to the mass of the object. To fully understand the impact of a force acting on an object we need a new concept. Momentum is the product of an objects mass and velocity. This considers not only how large an object is but how fast it is moving as well. Since velocity is one component it is a vector quantity as well. Momentum uses the greek symbol rho or an italicised p, so rho = mV or p = mV. The units associated with momentum are kg *m/s. Newtons first law declares that when no net force acts on an object it will move at a constant velocity, even if that velocity is zero. Since mass is a constant, this means that when no net forces act on an object, the objects velocity and thus momentum are constant. This explains the Law of Conservation of Momentum which says that in a closed system, momentum is conserved unless an outside force acts on the system. Newtons second law, F = m/a can be rewritten to substitute the equation for acceleration into the equation so F = m /\v/t . If we solve for m/\v we have the change in momentum. Rearranging the equation above we find that F/\t = m/\v. This means a change in momentum is caused by a force that acts on an object for some duration of time. This force over time is called an impulse. An impulse causes momentum to change so we can say that impulse equals a change in momentum which is the equation above . This is the root of the Impulse-Momentum theory which declares that a net force acting on an object for a time will cause a change in momentum. This is the principle behind airbags. By slowing down the deceleration or impact time it reduces the force the body experiences. All momentum is conserved, whether it is linear momentum or circular (angular) momentum. Angular momentum depends upon a force acting over some time plus the distance the force acts from the center of rotation. So basically angular momentum depends upon torque and the time the torque is acting. Remember Kepler's Laws of Planetary Motion? Basically since the force of attraction varies it conserves angular momentum. This conservation of momentum is true only within a closed system. By system we mean a specified collection of objects under consideration. In a closed system, no objects enter or leave the system. Internal forces may alter the individual momentum of objects but the system momentum will remain unchanged. Only an external force can alter the total momentum. To calculate individual changes in momentum we set the initial and final momentum equal to each other or the loss of momentum of one equals the gain in momemtum of the other. m1V1 = m2V2





		This page was last updated on: November 6, 2001