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MOMENTUM IMPULSE CONSERVATION OF MOMENTUM One-dimensional motion p mv impulse F t F 0 p 0 J F t m v m u + v>0 v<0 m m p=mv>0 p=mv<0 mass of object m [kg] velocity of object v [m.s-1] momentum of a moving object p [kg.m.s-1] impulse acting on object impulse J [N.s or kg.m.s-1] force acting on object F [N] time interval of force acting on object t [s] v1 = u force F acts time t v2 = v m m initial momentum p1 final momentum p2 J F t m v m u Impulse = Change in momentum of object initial velocity of object u, final velocity after a time interval t is v Launching a rocket momentum of rocket procket FRG force on rocket by gas FGR force on gas by rocket momentum of exhaust gases pgases Equation Mindmap eq04: Doing Physics on Line 1 Newton’s third law FRG FGR FRG t FGR t Forces act for time interval t impulse: Impulse = Change in momentum: pR pG (mv)rocket (mv)gases pR pG 0 Momentum is conserved: If net force acting on object is zero impulse is zero no change in momentum of object Law of Conservation of Linear Momentum F 0 p 0 p1 p2 initial momentum = final momentum In an isolated system (zero net force acting) then in any collisions or explosions within the system, momentum is conserved psystem 0 Beta decay - electron e- or positron e+ released from a nucleus had a continuous range of energies. Why? no. particles detected 210Bi 83 210Po 84 + e- + e KE of particles (MeV) Correct explanation proposed by Pauli (1930) – a third neutral particle called a neutrino must also be produced in the decay for energy and momentum to be conserved. For each beta emission, the total energy carried away from the decaying nucleus would be shared between the beta particle and the neutral particle emitted with it - it would be expected that the beta particles emitted would have a range of energies depending on the energies of the neutral particles emitted with them. In 1934, Italian physicist Enrico Fermi named Pauli’s particle the neutrino (), meaning “little neutral one” in Italian, and formulated a theory of decay using this particle. Fermi’s theory successfully explained all experimental observations. Equation Mindmap eq04: Doing Physics on Line 2 Neutron a constituent of the nucleus unknown radiation protons ionization chamber polonium particle source Be paraffin block Joliot’s Experiment Chadwick (1932) proposed that the radiation emitted from the Be target after it was bombarded by particles was a new type of neutral particle – the neutron (originally proposed by Rutherford). He then applied the conservation of energy and momentum laws to his experimental results and showed that the particles emitted from the Be had to be neutral with about the same mass as the proton. Chadwick had indeed discovered the neutron. 4 He2 + 9Be4 12 C6 + 1n0 Following Chadwick’s discovery of the neutron, a new model of the nucleus was proposed the nucleus consists of protons and neutrons. Together these particles are called the nucleons – particles that make up the nucleus: nucleon is a generic term for a proton or a neutron Equation Mindmap eq04: Doing Physics on Line 3