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<title>ReadingGuide_Ch6_Solution</title>
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<h1><strong>Chapter 5 – Newton’s Laws of Motion</strong></h1>
<h3><strong>Introduction</strong></h3>
- In Figure 5.1, The forces on the bridge are in ______________, so it stays in
place. <span id="ans">Equilibrium. </span>
<h3>5.1 Forces</h3>
- What is kinematics? What is Dynamics? <span id="ans">Kinematics – study
of motion. Dynamics – study of how forces affect the motion of
objects.</span>
<p>- Who is Newtonian Mechanics named for? <span id="ans">Isaac Newton</span>
</p>
<p>- What is force? Is it a scalar or vector? <span id="ans">A push or pull. A
vector. </span></p>
- What is a free-body diagram? What forces are drawn on it? <span
id="ans">Sketch showing all external forces action on an object. Only external
forces. </span>
<p>- What is the problem-solving strategy for drawing free-body diagrams? <span
id="ans">Draw the object. Include all forces that act on the object,
representing these forces as vectors. Resolve all force vectors into x- and
y-components. Draw a separate free-body diagram for each object in the problem.
</span></p>
<p>- What is a restoring force? <span id="ans">Force exerted on an object to
return it to its relaxed state.</span> </p>
<p>- What are contact forces? Field forces? <span id="ans">Contact forces are
caused byphysical contact between objects.</span> </p>
<p>- What is a newton? What combination of base units is the Newton equivalent
to? <span id="ans">SI unit of force. kg*m/s^2.</span> </p>
<p>- The resultant of two forces causes a mass to ______________. <span
id="ans">Accelerate. </span></p>
<p>- What is net external force? <span id="ans">Vector sum of all external
forces acting on a system. Equation 5.1. </span></p>
<h3>5.2 Newton’s First Law</h3>
- What is Newton’s first law?<span id="ans">A body at rest remains at
rest, or, if in motion, remains in motion at a constant velocity unless acted
on by a net external force. </span>
<p>- Is friction an external force? <span id="ans">Yes.</span> </p>
<p>- What is mass? Gravitation? <span id="ans">Mass is a measure of the amount
of something. Gravitation is the attraction of two masses.</span> </p>
<p>- What is inertia? What is the law of inertia known as? <span
id="ans">Inertia is the ability of an object to resist a change in motion. The
law of intertia is also known as Newton’s first law.</span> </p>
<p>- What is an inertial reference frame? <span id="ans">A reference frame
moving at constant velocity relative to an inertial frame is also inertial. A
reference frame accelerating relative to an inertial frame is not inertial.
</span></p>
<p>- What does it mean for a system to be in equilibrium? <span id="ans">The
forces on a system are balanced. </span></p>
<p>- What does Equation 5.2 say? <span id="ans">A net force of zero implies
that the velocity of the object is constant. </span></p>
<p>- If a car is moving at constant velocity, what is the net force acting on
it? See Figure 5.9. <span id="ans">Zero. </span></p>
<h3>5.3 Newton’s Second Law</h3>
- An external force causes ___________ acceleration. <span
id="ans">Nonzero.</span>
<p>- The _________ the mass, the smaller the acceleration produced by a given
force. This means that acceleration and mass are inversely proportional. <span
id="ans">Larger. </span></p>
<p>- What is Newton’s second law? <span id="ans">Equation 5.4.</span> </p>
<p>- Understand Example 5.2 to see how to apply Newton’s second law. What
is the direction of the acceleration? <span id="ans">The same direction as the
net force.</span> </p>
<p><span id="comm">On pdf version page 215, and Example
5.3 on pdf version page 221. From the errata: “Beginning on page 219 an
incorrect explanation for the forward motion of an automobile is given and then
repeated. The last paragraph states that the friction force opposes the forward
motion and the "engine force". The engine force is not an external force and in
fact, it is the frictional force that propels the car forward. The frictional
force opposes the drag forces and these are balanced for a car with constant
velocity. Example 5.1b page 220 repeats this inaccuracy. Example 5.3 on page
225 also repeats the notion that the friction between the road and the tires is
backwards for a forward moving and forward accelerating car. This is also
incorrect. The only time the friction is backwards is if the car is braking to
a halt. These sections and examples should be completely rewritten. What is
Newton’s second law in component form? Equation 5.5. Understand Examples
5.5 – 5.7.What is momentum? Equation 5.7. </span></p>
<h3>5.4 Mass and Weight</h3>
<p>- What is weight? <span id="ans">Force due to gravity in a mass. </span></p>
<p>- Is weight the same thing as mass? How are they related? <span
id="Mass"><span id="ans">No. Mass doesn’t change, weight is on
object’s mass times its acceleration.</span> </span></p>
<p>- If you were on another planet, would your weight or mass change? Neither?
Both? <span id="ans">Mass stays the same because it is intrinsic to the body.
The weight changes because the acceleration due to gravity changes. </span></p>
<p>- What does it mean for an object to be in free fall? <span id="ans">The net
external force equals its’ weight. </span></p>
<p>- Mass is an _____________ property of matter. <span id="ans">Intrinsic.
</span></p>
<h3>5.5 Newton’s Third Law</h3>
- What is Newton’s third law? <span id="ans">Equation 5.10. </span>
<p>- What is the third law loosely referred to as? <span id="ans">Action
reaction. </span></p>
<p>- In the discussion of the swimmer and Figure 5.16, the magnitude of what
force is equal to the magnitude of the feet on the wall force? <span
id="ans">Wall on the feet.</span></p>
<p>- What is the reaction force acting on the rocket? Thrust. </p>
<p>- What are two important features of Newton’s third law listed in the
text ? <span id="ans">The forces exerted (the action and reaction) are always
equal in magnitude but opposite in direction. These forces are acting on
different bodies or systems. </span></p>
<p>- Understand Example 5.10 and 5.11 to understand how to choose a system and
action-reaction forces. </p>
<h3>5.6 Common Forces</h3>
- What is a normal force? <span id="ans">The force supporting the weight of an
object, or a load, that is perpendicular to the surface of contact between the
load and its support; the surface applies this force to an object to support
the weight of the object. </span>
<p>- What is the vector form of the normal force of an object resting on a
horizontal surface? Its magnitude? <span id="ans">Equation 5.11 and 5.12.
</span></p>
<p>- In Example 5.12, why is the normal force pointing at an angle as opposed
to opposite the weight vector? <span id="ans">It is perpendicular to the
surface. </span></p>
<p>- Using a tilted coordinate system is often convenient. See Figure 5.23.</p>
<p>- What is tension? <span id="ans">A pulling force that acts along a
stretched flexible connector, such as a rope or cable. </span></p>
<p>- In Example 5.13, is the majority of the tension in the horizontal or
vertical direction? <span id="ans">Horizontal. </span></p>
<p>- Friction is a __________ force opposing motion. <span
id="ans">Resistive.</span> </p>
<p>- What restoring force do springs experience? What is k? The equation in the
middle of pdf page 245 is called Hooke's Law and is important even though it
isn't numbered. <span id="ans">F = - kx. K is the spring constant, it
represents the springs stiffness. </span></p>
<p>- What is the difference between real and fictitious forces? <span
id="ans">Real forces have a physical origin. Fictitious forces arise because the
observer is accelerating. </span></p>
<p><span id="comm">- At the top of pdf version page 246,
in Real Forces and Inertial Frame the errata contain the explanation “I
think the Coriolis force discussion gets the wrong sign. I think the following
statements in the book are wrong because they say the satellite feels a force
to the west (should be east, the satellite curves to the east): "... if a
satellite is heading due north above Earth’s Northern Hemisphere, then to
an observer on Earth, it will appear to experience a force to the west that has
no physical origin. Instead, Earth is rotating toward the east and moves east
under the satellite. In Earth’s frame, this looks like a westward force
on the satellite ... In the example of the satellite, the reaction force would
have to be an eastward force on Earth." The issue: the Coriolis force in the
northern hemisphere is to the east (not west) for a satellite moving north.
Thus ocean currents in the northern hemisphere are clockwise. Figure 10 shows a
counterclockwise hurricane, but that is because it is a low pressure storm
(high pressure storms rotate clockwise in the northern hemisphere). “ How
should this be written in the reading guide? What question do you ask to
determine if a force is real or fictitious? “What is the reaction
force?” </span></p>
<h3>5.7 Drawing Free-Body Diagrams</h3>
- What is the problem-solving strategy for drawing free-body diagrams? <span
id="ans">Draw the object. At first, you may want to draw a circle around the
object of interest to be sure you focus on labeling the forces acting on the
object. We often place this point at the origin of an xy-coordinate system.
Include all forces that act on the object, representing these forces as
vectors. Consider the types of forces (normal force, friction, tension, and
spring force, weight applied force). Do not include the net force on the
object. Convert the free-body diagram into a more detailed diagram showing the
x- and y-components of a given force. If there are two or more objects, in the
problem draw a separate free-body diagram for each object. </span>
<p>- In Example 5.16, is the acceleration of mass 1 equal to the acceleration
of mass 2? Why? <span id="ans">Yes, because they are connected with rope.
</span></p>
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