Chapter 5 Newton’s Second Law of Motion- Force and Acceleration
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Chapter 5 Newton’s Second Law of Motion- Force and Acceleration. Conceptual Physics Hewitt, 1999. 5.1 Force Causes Acceleration. To change velocity, you need to accelerate, decelerate or change direction The only way to change something’s state of motion is to apply a force - PowerPoint PPT Presentation
Transcript of Chapter 5 Newton’s Second Law of Motion- Force and Acceleration
Chapter 5 Newtons Second Law of Motion- Force and Acceleration
Conceptual PhysicsHewitt, 1999Chapter 5Newtons Second Law of Motion- Force and Acceleration5.1 Force Causes AccelerationTo change velocity, you need to accelerate, decelerate or change directionThe only way to change somethings state of motion is to apply a forceThe more you apply a force, the more you can change somethingAcceleration ~ Force~ means directly proportionalAs one changes, the other changes in the same mannerIf force doubles, acceleration doublesExample: Hours preparing for class (HW & studying) ~ grade earnedNet Force- the sum of all forces; dictates accelerationRecall: acceleration = (change in velocity) / (time interval)a=Dv/Dt5.2 Mass Resists AccelerationIf mass has inertia and inertia resists change, the more mass you have, the more resistant it is to changeAcceleration ~ 1/massInversely proportional to each otherAs one changes, the other changes in the opposite mannerIf mass doubles, acceleration is cut in halfExample: Keeping your room clean ~ 1/(mom yelling at you)5.3 Newtons Second LawThe acceleration of an object is equal to the net force acting on the object, divided by the mass of the object.a = F/mAlso can be used as F=ma
5.4 FrictionFriction- acts in the opposite direction to the applied forceCaused by surface irregularitiesRough and scratchy versus smooth and silkyHigh friction makes you need larger forcesLow friction allows for smaller forces to get the same acceleration
Physlet I.4.4
DragDrag force- the force exerted by a fluid on the object moving through the fluidGas or liquidDependant on size and shape of object, properties of fluid, velocity of object
5.5 Applying Force- PressureAlthough the weight of a book on the table wont change depending on which way it lays, the amount of pushing you have to do to get it to move will changeWhen the book is flat, you need to push harder than when it is on its edge because there is more area in contact with the tablePressure- force per unit of areaP = F/AMeasured in Pascals (Pa)
Bed of NailsWould you rather sit on a single nail?Or would you rather sit on 900 nails?
5.6 Free Fall ExplainedGalileo explained that regardless of the size of the object, it will fall at the same rate (1kg vs 100kg cannon ball)A larger mass has more gravity acting on it than a smaller massSince the acceleration due to gravity is always g (9.8 m/s2), F/m will always be true, regardless of mF/m = F/mExample: Find g for both cannonballs.For 1kg: a = F/m = weight/mass = (9.8x1)/1 = 9.8m/s2For 100kg: a = F/m = weight/mass = (9.8x100)/100 = 9.8m/s2Elephant vs Man
5.7 Falling and Air ResistanceTerminal velocity- reached when drag force equals the force of gravityAn application of dragOnly present when air is presentNo air resistance in a vacuum
New Formulae & AssessmentsP=F/A
Review Questions 1-18
Think & Explain 1-10
