Chapter 7 notes - Chapter 6 Momentum in an isolated system...

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Chapter 6 Momentum in an isolated system is always conserved. - A collision may result from physical contact between two objects In any interaction as long there is a force pushing against something then the forces are equal and opposite. You cannot have a perfectly elastic collision.na little bit of energy went into the system. Not all of the energy dissipated. You do not want a car to bounce off of a bridge when it hits it, because it means the change in acceleration is greater and the momentum is greater. You need to know conservation of kinetic energy!!! You need the equation its in the book. In elastic collisions both momentum and kinetic energy are conserved. In an inelastic collision momentum is conserved but kinetic energy is not. In a perfectly inelastic collision momentum is conserved, kinetic energy is not, and the two objects stick together after the collision, so the final velocities are the same. Chapter 7 Rotational Motion and The Law of Gravity The Radian The radian is a unit of angular measure The radian can be defined as the arc length s along a circle divided by the radius r s/r = theta More About Radians Comparing degrees and radians 1 radian = 360/2pi Converting from degrees to radians Theta(rad)=pi/180 theta(degrees) Angular Displacement Axis of rotation is the center of the disk Need a fixed reference line During time t, the reference line moves through angle θ Rigid Body Every point on the object undergoes circular motion about the point O All parts of the object of the body rotate through the same angle during the same time The object is considered to be a rigid body
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This means that each part of the body is fixed in position relative to all other parts of the body Angular Displacement, cont. The angular displacement is defined as the angle the object rotates through during some time interval The unit of angular displacement is the radian Each point on the object undergoes the same angular displacement Average Angular Speed The average angular speed, ω, of a rotating rigid object is the ratio of the angular displacement to the time interval Angular Speed, cont. The instantaneous angular speed is defined as the limit of the average speed as the time interval approaches zero Units of angular speed are radians/sec rad/s Speed will be positive if θ is increasing (counterclockwise)
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