# Physics

Alex Newton Chapter 8 Summary Recitation # 4

Linear Motion is a product of specific systems mass and its velocity. Linear momentum is a vector quantity. Linear motion acts in the same direction as the velocity direction of a body. Several principles have been made to explain the theory behind linear motion. This chapter looks at these set principles which govern bodies in momentum. From Newtons second law of momentum “The net exterior force is the same as the change in momentum of a system allover the time over which it changes”. The relationship between force and momentum exist if and only if mass is a constant. Impulse is an integral of force over an interval of time for which it acts. Since force is a vector quantity, then impulse is a vector quantity acting in the direction of the force. Impulse has a standard unit of measurement usually newton second. Any resultant force causes acceleration resulting to change in the velocity of a body. This depends on the exposure period and the amount of force exerted. A bigger change in linear motion will result from a large force exacted. Momentum can be conserved, revisiting the Newtons law “action and reaction forces are equal and opposite”. This law can be used to prove that in every single interaction there is a pair of contradicting force. For the system of the forces acting against each other to balance, the force should be equivalent. The law of momentum conservation states that for colliding bodies the momentum before and after colliding is equal. This means that the moments lost by the first body should be equivalent to the moments attained by the second body. Elastic impact is an encounter amongst bodies whereby the overall dynamic energy is conserved. Dynamic energy is the work required to speed-up a body whose mass is known from its state of rest to a certain velocity. Energy that a body possess at its state of rest is potential energy. This means that the dynamic energy within the bodies earlier or at the latter of a collision do not change. Net conservation of kinetic energy does not occur because during the collision some energy is transformed to heat or noise. In the energy conversion a state of repulse is reached first (potential energy) before transformation to other forms of energy. An inelastic collision in one-dimension results to a change in the interior dynamic energy which is not preserved. After the impact, the objects may twig together resulting a perfect inelastic collision situation resulting to a reduction in internal kinetic energy. Collision of bodies may occur in two dimensions. This assume a case of a body in motion colliding with a body at rest (velocity=0). After the collision the velocity of the body in motion decrease meaning the collision results to loss in kinetic energy. Lastly, rocket propulsion uses the principle of Newtons third law which conditions action and rejoinder forces to be equivalent and contrary. The acceleration of a skyrocket depends on the drain of blasts velocity which triggers its acceleration. An explanation of skyrocket at the lift-off stage, the motors of the skyrocket force hot air out. Proving the law associated, the burning gases thrust the rocket in the opposite (vertical) direction. This action results to the propulsion of the skyrocket. If the rocket burns its fuel at a faster rate the its acceleration is fast too and finally the slighter the skyrocket mass the higher the rate at which it speeds-up. The thrust increases as the skyrocket reduces its mass meaning that the change in velocity will increase with time. This can also be explained by the reduced pull by the gravitational force.