Exam 1: Chapters 1-4
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Exam 1: Chapters 1-4 60% Problems – one problem from WebAssign with different numbers Understand homework problems Review notes and text Try new problems 40% Multiple Choice Questions Review Power Points (on web page) Review Before Class Assignments Try Questions

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Exam 1: Chapters 1-4 60% Problems – one problem from WebAssign with different numbers

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  • Exam 1: Chapters 1-4

  • 60% Problems – one problem from WebAssign with different numbers

    • Understand homework problems

    • Review notes and text

    • Try new problems

  • 40% Multiple Choice Questions

    • Review Power Points (on web page)

    • Review Before Class Assignments

    • Try Questions

  • Graphs, Pictures and Drawings (Sketches)

  • Don’t rely on memorized equations


Chapter 5 The Laws of Motion

5-1a Force – a push or pull.

  • CT1: The force of the elevator on Norbert and Zot is

  • up.

  • down.


Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon.

  • CT2: The force of the non-sticky elevator surface on Norbert and Zot is

  • up.

  • down.


Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon.

  • CT3: The acceleration of Norbert and Zot is

  • up.

  • down.

  • zero


Fig. 5.1, p.113


5-1 B. Mass

The mass of an object is the amount of matter (stuff) in that object. It is the same for a given object everywhere in the Universe. Mass is also called inertia because it resists being moved.


5-2 Newton’s First Law: A body remains in uniform motion (or at rest) unless acted upon by a net external force.

  • acceleration due to Earth’s rotation  0.03 m/s2

  • acceleration due to Earth’s orbit  0.006 m/s2

  • acceleration due to Sun’s orbit  2 x 10-10 m/s2

An inertia frame of reference is a coordinate system (or frame) in which Newton’s Law’s hold.

We will assume that the Earth’s surface is an inertial frame and not make errors greater than 0.03/10 = 0.3%.


A.

B.

C.

D.

E.

CT4


A.

B.

C.

D.

E.

CT5


5-3 Newton’s Second Law: The net external force is equal to the mass times the acceleration.

F = ma

Force and acceleration are vectors

  • Fx = max

  • Fy = may remember Galileo!

  • Fz = maz

Normally we will do problems in a plane with only x and y components.


Calibrating a “Force Meter”

Experiments show forces add as vectors.


Acceleration is Proportional to Force


Acceleration is Inversely Proportional to Mass


Applications of Newton’s Laws - Method

  • Draw picture of the problem.

  • Choose body (bodies) to isolate.

  • Draw Free Body Diagrams (FBDs) for isolated bodies.

  • Choose and label coordinate axes.

  • Apply Newton’s 2nd Law: Fx = max and Fy = may

  • Solve for F, m or a.

  • Work out kinematics.

  • Check solution is reasonable.

P5.6 (p.136)


  • Concept Question 6

  • P5.6b: If the parachutist comes to rest over a shorter distance, the force exerted by the ground will be

  • greater.

  • less.

  • the same.


FAB

A

B

FBA

5-4 Newton’s Third Law: If body A acts on body B, then body B acts back on body A with a force equal in magnitude but opposite in direction.

FAB and FBA are 3rd Law pairs.


CT7

A.

B.

C.

D.

E.


P5.18

(p.137)

  • Concept Question 8

  • P5.18b: If the 5 N force is applied to the heavy box instead, the contact force between the boxes will be

  • greater.

  • less.

  • the same.


5-5 The Vector Nature of Forces

Two Astronauts Pushing a Satellite with Forces that Differ in Magnitude and Direction


P5.22 (p.137)


P5.28 (p.138)


Orbit of Moon about the Sun

Actual

Exaggerated and incorrect


y

x

5-6 Gravitational Force or Weight

Fg = mg (weight)

g = -9.81 j (m/s2 )

Apparent Weight is the force you actually feel pushing on you – often the floor.


P5.35 (p.138)


  • Concept Question 9

  • P5.35b: If the constant speed of descent is greater than 1.1 m/s, the force of air resistance is

  • greater.

  • less.

  • the same.


  • Concept Question 10

  • P5.33a: Your normal weight is 610 N and the scale in the elevator reads 720 N. The acceleration of the elevator

  • upward.

  • downward.

  • zero.


  • Concept Question 11

  • P5.33c: Your normal weight is 610 N and the scale in the elevator reads 720 N. The magnitude of the velocity of the elevator is

  • increasing.

  • decreasing.

  • zero.

  • impossible to determine without more information.


5-7 Normal ForcesThe Normal Force May Equal the Weight


The Normal Force May Differ from the Weight


An Object on an Inclined Surface

P5.42 (p.138)


  • Concept Question 12

  • P5.42b: If the angle of the incline is decreased, the normal force will

  • increase.

  • decrease.

  • stay the same.


A.

B.

CT13


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