PLTW Final Exam Study Guide Questions with Complete Solutions Precision - Correct Answer Engineers communicate precisely to others Use clear definitions State the meaning of variables Are careful about specifying units Calculate accurately Express answers with a degree of precision appropriate for the problem context Why is it important to use constraints when sketching with your 3D modeling program? - Correct Answer Because constraints allow you to move shapes accordingly in order to best represent the object you are sketching.Why are some constraints automatically applied by the software, but you must manually apply others? - Correct Answer Because some shapes come with automatic constraints. Squares for instance, have two sets of parallel sides and all sides are equal in length.Fillet - Correct Answer A curve formed at the interior intersection between two or more surfaces.Explain the difference between weight and mass. - Correct Answer Weight is the force of gravity acting upon an object, while mass is the quantity of matter in an object.Density - Correct Answer a measure of the amount of matter per unit of volume Matter: Mass vs. Weight - Correct Answer Mass is the amount of matter in an object or the quantity of the inertia of the object.Weight is the force of gravity on mass.W = weight m = mass g = acceleration of gravity SI units weight and mass - Correct Answer mass = kilograms and weight = newtons 1 / 3
Us Customary weight and mass - Correct Answer mass = slugs, more commonly pound-mass(lb^m) 1 lbm = 0.45359237 kg and weight = pounds How are pound-mass and pound-force related? - Correct Answer On Earth (g = 32.174 ft/s2): 1 pound-mass object weighs 1 pound-force
In outer space (no gravity): 1 pound-mass object has no weight
On the moon (g = 5.32 ft/s2): 1 pound-mass object weighs 0.166 pound-force
How can density be indicated? - Correct Answer Mass density and weight density Mass/Weight Density - Correct Answer Mass Density commonly used for SI units g/cm3 or kg/m3 Weight Density commonly used for U.S. Customary units lb/in.3 or lb/ft3 Balance—measures mass - Correct Answer Uses objects of known mass to find the unknown mass of an object Measurement is unaffected by difference in gravity Scale—measures weight - Correct Answer Measures force caused by gravity Measurement is affected by difference in the acceleration of gravity May display a "mass" measurement reading by using an assumed acceleration of gravity to convert from weight to mass Volume: Measurement - Correct Answer Volume is the amount of three dimensional space enclosed by an object.
Finding Volume:
Calculate using geometry of object Measure indirectly using water displacement (or 3D scanner) Surface area - Correct Answer is the sum of all the areas of the faces of a three-dimensional solid.Types of forces - Correct Answer Contact and action-at-distance 2 / 3
Contact forces - Correct Answer result when two object physically touch each other. No contact force if objects don't touch Action-at-distance forces - Correct Answer result even when tow interacting object are not physically in contact. Gravity is an action at a distance force.Applied contact forces - Correct Answer because one object applies a force to another object A force that resists the contact pull of gravity toward the center of the earth is called - Correct Answer Contact force Normal Force - Correct Answer A contact force that results when an object rests on a surface, always acts perpendicular to the supporting force Friction - Correct Answer Resists a sliding movement Free body diagram - Correct Answer It represents all of the forces acting on an object Vectors - Correct Answer Arrows representing forces, the length of arrow represents the magnitude of the force Static equalibrium - Correct Answer Object is not moving in any direction Moment of a force - Correct Answer a turning force, it's caused by a force acting on a object at a point some specific distance from a fixed point Moments - Correct Answer Counterclockwise(CCW)= positive Clockwise(CW)= negative Mp = F*d - Correct Answer The magnitude of a moment about a point,p F= magnitude of force d= perpendicular distance
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