chapter 4 newton’s first law of motion- inertia
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Chapter 4 Newton’s First Law of Motion- Inertia. Conceptual Physics Hewitt, 1999. 4.1 Aristotle on Motion (400B.C.). Divided motion into two categories: Natural motion- falling (boulders) or rising (smoke) Violent motion- applying a force to make something move, “against its nature”. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 4 Newton’s First Law of Motion-
InertiaConceptual Physics
Hewitt, 1999
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Divided motion into two categories:◦ Natural motion- falling (boulders) or rising
(smoke)◦ Violent motion- applying a force to make
something move, “against its nature”
4.1 Aristotle on Motion(400B.C.)
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Heliocentric view- earth around sun Worked in secret to avoid persecution
4.2 Copernicus on Motion (1543A.D.)
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Force- any push or pull◦ Friction- force that acts when two
things physically interact◦ Only when friction is present will
something have its state of motion changed
Inertia- every object resists change in its state of motion (velocity)◦ If moving, wants to keep moving◦ If stationary, wants to sit still
4.3 Galileo on Motion(1600’s A.D.)
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Friction Ramp
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“Every object continues in its state of rest or uniform velocity as long as no net force acts on it.”
4.4 Newton’s Law of Inertia
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Example: Kick an empty paint can and it flies. Kick a paint can filled with paint and you break your toe.◦ The can with more “stuff” in it has more inertia: more resistance
to change in motion (or lack of motion). Mass is not volume
◦ Mass- measured in kilograms (kg) and is a statement of how much matter it contains Most fundamental measurement of quantity of matter Independent of location
◦ Volume- measured in milliliters (mL) or liters (L) and is a statement of how much space the matter takes up
4.5 Mass- A Measure of Inertia
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Weight- the force of gravity on an object◦ On Earth, Mr. Latham has a mass of 85kg and 185lbs◦ In deep space, far away from anything, he still has a
mass of 85kg, but no weight (weightless)
Weightlessness- your apparent weight is 0N◦ If your “a”=g◦ If your “a”≈0m/s2
◦ Think free falling◦ http://www.youtube.com/watch?v=2V9h42yspbo
Mass is not weight
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Mass is not weight
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One kg weighs 9.8 Newtons (on Earth)◦ 1kg = 9.8N◦ Force is measured in Newtons (N)
Force of gravity (weight) = (mass)(acceleration due to gravity)◦ Fg=mg
Remember that on Earth a=g=9.8m/s2
On the Earth’s moon, g=1.63m/s2
Mass & Force
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Net force- sum of all of the forces acting on the object
Force (free-body) diagram- shows vectors of all forces involved in motion◦ Use arrows, length matters, to show the force(s)
involved◦ Helps us visualize what’s going on
4.6 Net Force
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Normal force- a supporting force: a table, the earth, etc.◦ Anything that holds an object (or you) up◦ Typically can support much more than just that one
object We only talk about the force that is used, not what is
available◦ Labeled as FN
Equilibrium- when all of the forces cancel each other out
4.7 Equilibrium- When Net Force Equals Zero
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As the angle gets larger, the resultant force is constant, but the actual forces must get larger as well
Hanging from a vertical string is easier than from a horizontal string
4.8 Vector Addition of Forces
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F=ma (force) Fg=mg (weight) Fnet=F1+F2
gE=9.8m/s2
gM=1.63m/s2
Review Questions 1-20
Think & Explain 1-12
Conceptual Development 4-1, 4-2, 4-3
Assessments & Formula