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