Chapter 5 - Forces

force – a ____ or ____ on an object causes _____ or causes a moving object ________ or change _______ if a force acts on an object the object moves in the _________ of that force

force – any push or pull forces differ because of __________ example – baseball thrown by MLB pitcher and ball thrown by little girl forces differ because of _______ example – baseball and softball ______, _____ and ________ are all related

all forces in nature come from the four elementary forces ______ _____force – holds atoms nucleus together ___________ force – like charges repel, opposite charges attract _______ force – force that causes radioactive decay ________ – force of attraction that causes all masses to attract to one another - electromagnetic and gravity most observed in our world

pound(___ or __) – English unit of force newton(__) – SI unit of force 1 N = force added to ______object that accelerates the object by _______ 1 lb = _______ N 150 lb person = 667.2 N

how forces act ________forces – objects need to be in direct contact with one another ________ ________, air resistance ________force “__-__-_______” forces – objects are not touching or connected _________ __________ ___________

________– force caused by gravitational field _______– force of gravity on an object ______N on Earth depends on ______and ________ a 10-kg rock weighs 98 N on Earth but only 16 N on the Moon weighs 6x less because there is 6x less gravity on the moon

5.2 Friction _______– the force that opposes sliding motion of two touching surfaces dependent on two factors the _____of _______ bumps between the two surfaces catch or form ‘____________’ all surfaces are rough on the micro-scale the _______pressing the surfaces together more force pushing the two objects together = stronger microwelds

_____friction – friction between two objects that are not moving relative to one another

________friction – force that opposes the motion of two surfaces sliding past one another. caused by ________continually breaking and forming again usually _____ than static friction a force must be continually supplied to overcome sliding friction

_______friction – the force between a rolling object and the surface it rolls on the force that opposes the motion of a rolling object the wheel, surface or both are _____ where they are in contact ______ friction acts on the deformed area

___ resistance – friction like force that opposes the motion of an object as it moves through air causes objects to fall at different speeds acts in the opposite direction of the objects motion factors that affect air resistance ____ of the object _____ of the object _____ of the object is not a factor

reducing friction _________ keeps two sliding surfaces from touching

_____ ______ changes sliding friction to rolling motion

_________levitation separate sliding surfaces with magnets supported on a cushion of air

Using friction brakes tires – groves increase friction when road is wet nails cleats or spiked shoes

friction changes NRG by wearing away moving objects friction & NRG friction changes NRG of _______into _____ NRG rub you hands together friction changes NRG by wearing away moving objects engines wear out tires go bald rocks become rounded and smooth

5.3 Forces & Equilibrium _____ force – sum of 2 or more forces acting on an object

_______ forces – forces on an object that are equal in size and opposite in direction net force = 0 = no motion

________ – all forces cancel out leaving a zero net force no motion

_______ forces – 2 or more forces on an object that are not equal in size net force – object moves in direction of greater force

_______ forces _______ force – aka support force force that acts “perpendicular” to the surface an object is pushing on it table exerts a normal force on the book it is holding up ______ in strength to the force pushing the object in to the surface table exerts an equal force to the weight of the book