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Chapter 4Chapter 4
Newton’s First Law of Motion:
Inertia
Newton’s First Law Newton’s First Law - Inertia- InertiaIn Fancy Terms: Every
object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.
In Plain English:In Plain English:
Objects in motion tend to stay in motion.Objects at rest tend to stay at rest.
InertiaInertia
Definition: the reluctance of any body to change its state of motion
Examples of Examples of InertiaInertia
Alphabet soupRemoving tablecloth with dishes still on the tablehttp://www.youtube.com/watch?v=QbGV6qQcJrw
http://www.youtube.com/watch?v=aCqQzrPCcFM&feature=related
So Why Do So Why Do Things in Things in
Motion Stop?Motion Stop?
ForcesForces
Definition: any push or pull
FrictionFriction
Definition: the force that acts between materials that touch as they move past each other
- - caused by caused by irregularities in irregularities in the surfaces of the surfaces of objects that are objects that are
touchingtouching
- - Even very smooth Even very smooth surfaces have surfaces have microscopic microscopic
irregularities that irregularities that obstruct motionobstruct motion
MASSMASS a measure of inertiameasured in kilograms
MASS AND MASS AND WEIGHT ARE WEIGHT ARE
NOT THE NOT THE SAME SAME
THING!!!THING!!!
MassMass: quantity of : quantity of matter in an objectmatter in an object- independent of - independent of locationlocation
WeightWeight: force of : force of gravity on an objectgravity on an object- depends on an - depends on an object’s locationobject’s location
Mass and Weight Mass and Weight are Proportional are Proportional but but NOTNOT Equal Equal
a lot of mass = a lot of weight
SI unit of mass – SI unit of mass – kilogramkilogram
SI unit of force - SI unit of force - NewtonNewton
1 kg = 9.8 Newtons 1 kg = 9.8 Newtons (N)(N)
weight = mass x weight = mass x gravitygravityw = mgw = mg
http://www.youtube.com/watch?v=aCqQzrPCcFM
Net ForceNet ForceDefinition: combination of all forces acting on an object
The net forces The net forces changes an object’s changes an object’s
state of motionstate of motion
In the absence of a In the absence of a net force, objects do net force, objects do
not change their state not change their state of motionof motion
Normal ForceNormal ForceDefinition: the upward force that balances the weight of an object
Also called support force
Other forces:Other forces:
Tension: At equilibrium – Tension = weight
EquilibriumEquilibriumNet force = zero
Chapter 5Chapter 5Newton’s 2nd
Law
Remember:Remember:
Acceleration = change in velocity
time interval
What causes What causes acceleration?acceleration?
Force
An objects acceleration An objects acceleration is directly proportional is directly proportional
to the net forceto the net force
Acceleration ~ net force
Mass resists Mass resists accelerationacceleration
Acceleration ~ 1/mass
(inversely proportional)
Newton’s 2Newton’s 2ndnd Law: Law:The acceleration produced by
a net force on an object is directly proportional to the
magnitude of the net force, is in the same direction as the net force, and is inversely
proportional to the mass of the object.
In other wordsIn other words::
Acceleration = net force/mass
a= F/m
Net ForceNet Force
Unit will always be Newtons.
1 N = kg*m/s2
Free Body Free Body DiagramDiagram
Definition: Diagram showing all the forces acting on an object.
Applying ForceApplying ForcePressure = force per unit of area
Measured in pascals (Pa)Pascal = N/m2
Pressure = Pressure = ForceForce area of area of applicationapplication
P = F/A
Pressure is Pressure is increased when increased when
surface area surface area decreases!decreases!
ex. bed of nailsex. bed of nails
Falling and Air Falling and Air ResistanceResistance
Terminal velocity: speed at which acceleration of a falling object is zero because friction balances weight
Free Fall ExplainedFree Fall Explained
F = F mm
Chapter 6Chapter 6Newton’s 3Newton’s 3rdrd
LawLawFor every action there is an equal and opposite reaction
AllAll actions actions occur in pairsoccur in pairs
ActionAction:: Object A Object A exerts force on exerts force on Object BObject BReactionReaction:: Object B Object B exerts force on exerts force on Object AObject A
Newton’s Law of Newton’s Law of Universal GravitationUniversal Gravitation
Every object is attracts every other object with a
force that for any two objects is directly
proportional to the mass of each object.
In other words, In other words, the greater the masses, the greater the masses, the greater the force of the greater the force of
attraction between themattraction between them
F = G F = G mm11mm22
d d
where G = 6.67 x 10where G = 6.67 x 10-11-11 Nm Nm22/kg/kg22
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