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Physics: Lecture 4: Momentum, Machines, and Radioactive Decay


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Momentum (p)
p = mv

a measure of a moving object's tendency to continue along its present path (a vector)
In an isolated system, momentum is always ________.
Elastic Collisions
-Mechanical Energy is conserved
Inelastic Collisions
-Colliding objects lose some of their mechanical energy to internal energy

p(initial) = p(final)
Impulse (J)
-The change in momentum

J = d(mv) = F(avg)*dt
Ideal Machines
-Ramp, lever, and pulley
-Reduce force, but don't change work
What happens when work is held constant?
force and distance are inversely proportional
Alpha Decay
-An alpha particle (helium nucleus, 2 protons, 2 neutrons) are lost
Beta Decay
-The expulsion of an electron, resulting in creation of a proton
Positron Emission
-The emission of a positron when a proton becomes a neutron. A proton is transformed into a neutron and a positron is emitted.
Gamma Ray
-High frequency photon
-Electron + Positron = 2 gamma rays
Rest Mass Energy
E = mc^2
Mass Defect
-Difference in energy between the nucleons and the individual particles
Binding Energy
-Energy holding the nucleons together, find by plugging in mass defect into E = mc^2
-The most stable nuclei have the strongest binding energy
T or F: Only fusion produces more stable nuclei
F: Both fission and fusion produce more stable nuclei

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