Unit 2 Forces & Motion

Forces

______- an _____ applied to an object to _______ its motion(push or pull)

Units of lb, N (equal to kg.m/sec2)If forces are _______ then the object won’t _______ and it is said to be in _________________ _________=acceleration

Forces ______ occur in pairs!!!!!

Newton’s Laws of MotionNewton’s First Law:

“AKA” the Law of _______Inertia- property of an object to ______ _______ in state of motion

an object will _____ at rest until ______ on by an unbalanced _______In other words, things tend to keep on doing what they were doing in the first place unless you apply a force.

Newton’s Laws of MotionNewton’s Second Law:

Unbalanced force causes an object to ________ while the object’s mass _____accelerationFnet=ma•a=acceleration (m/sec2), F=

force (N), m=mass (kg)• Fnet= Right – Left

• Fnet= Top - Bottom

EX. Lighter cars go faster than heavier ones pushed with equal force. Lighter cars resist the force of acceleration less allowing them to move faster than heavier ones.

3.3 Newton’s Third Law

Newton’s 3rd Law: For ______ _____ ______ there is a reaction force equal in ________ & __________ in directionCan be _______ or __________Examples: rockets, stepping into a boat, throw a ball when on a skate board

Net Forces____ Force - ____ _____ of all the forces that act on an objectIn the same _______ – ____ forces togetherIn ________ directions –_______ forces

largest vector wins when forces act in opposite directions

At right angles (a2 + b2 = c2)When net Force = 0, there is __ ____________. This means the object is:

Not moving ORMoving at a constant velocity

Gravity, Weight & MassGravity-

Force ______ toward mass of planetDepends on _____Mass- _______ of matter in an object ________ ___ __ ________

Changes on other planetsOn Earth= -9.8m/s2

Weight- force ________ by _____, depends on mass

It is a force acting on object in units of lb or N

•Fw=mg

•Fw= weight force (N)

•m=mass (kg)

•g=acceleration due to gravity (-9.8 m/sec2)

•Fw=mg

•Fw= weight force (N)

•m=mass (kg)

•g=acceleration due to gravity (-9.8 m/sec2)

Fw

m g

Law of Universal Gravitation

______ __ _________ directly related to masses & indirectly related to distanceF=G m1m2

r2

F= Force of attraction G= ___________ constant m1 = mass object 1 m2 = mass object 2 r = radius btw the objects

Free Fall- • ____ straight down in the ________ of ___

_____________• Acceleration due to gravity _____ m/sec2

• Object’s will experience _______ acceleration (uniform increases in velocity) when in _____ ________!

Terminal Velocity- Highest ________ reached by a ________ objectWhen an object ______ _________, but continues to fall, terminal velocity is achieved.Occurs when force of air resistance _________ the weight of the object.

Friction: _________ accelerationWorks __________ motionOccurs when surfaces move against one anotherCauses _______ on parts

Examples of friction:_____ friction- (air resistance)- aka – “____”_______ friction (rub hands together)________ friction- (oil in car engines & joint fluid)________ friction- (wheel on road, ball bearings)

What is friction?

Static Friction (Ffs) Sliding Friction (Ffk) The frictional force that must be ________ to get an object moving (Ffs)

μs = Ffs

FN

μ=coefficient of friction (ratio of frictional forces to the normal force)

Fw: Weight Force= mass(gravity)

FN: Normal Force Often = to the Weight Force (Fw)

The frictional force that ______ once an object is in motion (Ffk)

AKA kinetic frictionμk = Ffk

FN

Free-body diagrams• It is a diagram that visually represents the various forces being applied on an object: •Fstatic = _______ force (Ff)

•Fpush = _______ force (FA)•N = the ______ or support force (FN); perpendicular to surface•W = _____ of object (FW)

The sum of all of the forces involved is called the FNET or FR ( the “R” stands for ____________ or the result of all forces)

Rules of Friction

If an object is slowing down or not moving, then the frictional force (Ff) is _________ the pulling forceIf an object is moving at a constant speed, then the frictional force (Ff) is _____ __ the pulling forceIf an object is speeding up, the frictional force (Ff) is _____ _____ the pulling force. Fp=pulling force = Fa=applied force

Fp or FaFf