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 forces1. ______ _____force – holds atoms nucleus

together2. ___________ force – like charges repel,

opposite charges attract3. _______ force – force that causes

radioactive decay4. ________ – 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 factors1) the _____of _______▪ bumps between the two surfaces catch or form

‘____________’▪ all surfaces are rough on the micro-scale

2) 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

1) ____ of the object2) _____ 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 frictionbrakestires – groves increase friction when road is wet

nailscleats or spiked shoes

▪friction & NRGfriction changes NRG of _______into _____ NRGrub 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 forceno 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 forceforce 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 surfacetable exerts an equal force to the weight of the book