Force & motion notes 2012

Teacher Friday, October 26, 2012 10:17:12 AM CT

When an objectWhen an object’’s distance from anothers distance from anotherobject is changing.object is changing.

You must have a You must have a reference pointreference point in inorder to determine if something is inorder to determine if something is inmotion.motion.


Does the sunDoes the sunmovemove

or the Earth?or the Earth?Don’t copythis slide.


The The pushpush or or pullpull on an on anobject.object.


ForceForce or or attractionattractionbetween twobetween twoobjects.objects.


Gravity and Motion

• The gravitationalconstant is 9.8 m/s².

• Objects fall to Earthat the sameaccelerationregardless of mass.


Measure of the force ofMeasure of the force ofattraction between anattraction between anobjectobject and and EarthEarth..

A A NewtonNewton is the metric unit is the metric unitused to measure weight.used to measure weight.


Many forces act together on anMany forces act together on anobject.object.

However, it is not alwaysHowever, it is not alwayseasy to determine whateasy to determine whatis exerting a force oris exerting a force orwhat is receiving a force.what is receiving a force.


When forces are applied in the When forces are applied in the samesamedirection, the forces are direction, the forces are addedadded together together..

Example: paddling a boat in the sameExample: paddling a boat in the samedirection helps the boat to go faster.direction helps the boat to go faster.



When forces are applied inWhen forces are applied inoppositeopposite directions, subtract directions, subtractthe smaller force to determinethe smaller force to determinethe direction.the direction.

Example: Example: tug-of-wartug-of-warTeacher Friday, October 26, 2012 10:17:12 AM CT

The resulting force is calledThe resulting force is calledthe the net forcenet force..



When a net force acts on anWhen a net force acts on anobject, the forces areobject, the forces areunbalancedunbalanced..

This causes an object to startThis causes an object to startmovingmoving, stop , stop movingmoving, or change, or changedirectiondirection..


Equal forces on an object inEqual forces on an object inopposite directions are calledopposite directions are calledbalancedbalanced forcesforces..

This does not change anThis does not change anobjectobject’’s motion.s motion.


Force between surfaces thatForce between surfaces thatresists the movementresists the movement of one of onesurface past another surface.surface past another surface.


Friction also existsFriction also existsbetween an object rollingbetween an object rollingacross another surface.across another surface.


Rate at which the Rate at which the positionpositionof an object changes.of an object changes.


Two units of measure are required toindicate speed.

1. Any unit of distanceEx: centimeters, meters

2.Any unit of timeEx: seconds, minutes, hour


A car travels at the speed of65 miles per hour (65 mph)

The speed of an object moving ina particular direction.


Includes both a Includes both a speedspeed and a and adirectiondirection..


Why would an airplane traveling Why would an airplane traveling westwest at at750 km/hr have a different velocity than750 km/hr have a different velocity thanan airplane flying an airplane flying southeastsoutheast at 750 at 750km/hr?km/hr?

The speed may be the same butThe speed may be the same butthe direction in which they arethe direction in which they areflying is different.flying is different.


Speed of a car:

65 miles/hour

Velocity of a car:

65 miles/hr to the west


The rate at which velocity is changing.The rate at which velocity is changing.

••Acceleration occurs when a movingAcceleration occurs when a movingobject object speeds upspeeds up, , slows downslows down, or, orchanges directionchanges direction..


•Any change in velocity is acceleration.•Slowing down is negative acceleration.

What would be an example ofWhat would be an example ofpositive acceleration?positive acceleration?

A car going from 0 mph to 65 mph.A car going from 0 mph to 65 mph.


Acceleration• Acceleration is the rate at which velocity

changes.• A=V/t or the object’s velocity divided by

time.• All objects accelerate towards Earth at

the rate of gravity.• To calculate velocity of falling objects,

the gravitational constant is multiplied bythe time it takes the object to fall.


What affects acceleration?• Air resistance is a

contributing factor toacceleration.

• Air resistance is a fluidfriction that opposes themotion of objects through air.

• The amount of air resistanceon an object depends on thesize, shape, and velocity ofthe object.

• The more surface area anobject has, the moresusceptible it is to airresistance.


Acceleration continues …• As the speed of a falling object

increases, the air resistanceincreases.

• This upward force of air resistanceincreases until it reaches thedownward force of gravity.

• At this point the object stopsaccelerating and continues falling at aconstant velocity called terminalvelocity.


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Force & motion notes 2012