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## SHORT QUIZ #2

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**SHORT QUIZ #2**Suppose you are measuring your waistline with a tape measure. The ends of the tape measure are as shown. Report the measurement with the correct significant figures. Convert the measurement in millimetres (1in = 2.54cm) and express it in scientific notation with 4 significant figures.**One-dimensional motion**Lecture #3 June 20 2013**Physical assumptions**Every theory has a set of assumptions which specify the scope of its validity. One must be careful to know all the assumptions made to arrive at a particular conclusion**Relativity**Speed is close to speed of light. Length scales are very large.**Quantum mechanics**Mass and length scales are small Zinc atom on a layer of copper oxide**Classical physics**• speed of the object << the speed of light • mass and length scales are comparable to “everyday objects”. • Ex: Air resistance and Coriolis force are neglected in projectile motion**Mathematical models**Mathematical models are used to idealize the physical system and simplify the calculations. The accuracy of the solution is dependent on the faithfulness of the mathematical model to physical reality.**Free fall and projectile motion**Projectile as point object: neglect rotational motion and microscopic fluctuations**Reference frames**In solving motion problems, it is important to specify the reference frame. For most of our purposes, the reference frame is one or two dimensional and at rest.**Motion**The only thing that constant in this world is change. All particles comprising the universe are in constant motion.**Two states of (translational) motion**• Motion with constant velocity • Accelerated motion**Kinematics: Study of how objects move**• Position • Distance and displacement • (Instantaneous and Average) Speed and velocity • (Instantaneous and Average) Acceleration**Position**Position specifies where the object is in space.**Distance versus displacement**Distance is the length of the trajectory of an object. Displacement is the change in position of the object with respect to the origin.**Speed versus velocity: Average**Average speed is the change in distance divided by change in time. Average velocity is the change in displacement divided by change in time.**Speed versus velocity: Instantaneous**Instantaneous speed Instantaneous velocity**Average and instantaneous acceleration**Average acceleration is the change in velocity divided by change in time. Instantaneous acceleration:**Equations of motion with constant acceleration**• Position: • Velocity: • Acceleration:**Free fall motion assumptions:**• The height is much smaller than the earth’s radius so that the acceleration is constant. • The apple is a point object; the motion is purely translational. • Only gravity influences the motion. Air resistance and other effects are neglected.**Free fall motion**Given any two information, say, an initial velocity and position, the whole kinematics of free fall motion can be worked out. Why two?**Projectile Motion isconstantly accelerated vertical motion +**motion with constant horizontal velocity**THREE POINTS:**• In the analysis of the motion of an object, one must know the underlying physical assumptions, use idealized models, and specify the reference frame. • The kinematics of an object can be described by the following scalar or vector quantities: position, distance, displacement, as well as, average and instantaneous speed, velocity and acceleration. • Free fall is the one-dimensional motion of objects under the influence of the Earth’s gravity only. If in two dimensions, we have projectile motion.