When an objectWhen an object’s distance from another’s distance from another
object is changing.object is changing.
You must have aYou must have a reference pointreference point inin
order to determine if something is inorder to determine if something is in
Does the sunDoes the sun
or the Earth?or the Earth?Don’t copy
TheThe pushpush oror pullpull on anon an
Force between surfaces thatForce between surfaces that
resists the movementresists the movement of oneof one
surface past another surface.surface past another surface.
Friction also existsFriction also exists
between an object rollingbetween an object rolling
across another surface.across another surface.
ForceForce oror attractionattraction
between twobetween two
Gravity and Motion
• The gravitational
constant is 9.8 m/s².
• Objects fall to Earth
at the same
regardless of mass.
Measure of the force ofMeasure of the force of
attraction between anattraction between an
objectobject andand EarthEarth..
AA NewtonNewton is the metric unitis the metric unit
used to measure weight.used to measure weight.
Many forces act together on anMany forces act together on an
However, it is not alwaysHowever, it is not always
easy to determine whateasy to determine what
is exerting a force oris exerting a force or
what is receiving a force.what is receiving a force.
When forces are applied in theWhen forces are applied in the samesame
direction, the forces aredirection, the forces are addedadded togethertogether..
Example: paddling a boat in the sameExample: paddling a boat in the same
direction helps the boat to go faster.direction helps the boat to go faster.
When forces are applied inWhen forces are applied in
oppositeopposite directions, subtractdirections, subtract
the smaller force to determinethe smaller force to determine
the direction.the direction.
The resulting force is calledThe resulting force is called
thethe net forcenet force..
When a net force acts on anWhen a net force acts on an
object, the forces areobject, the forces are
This causes an object to startThis causes an object to start
movingmoving, stop, stop movingmoving, or change, or change
Equal forces on an object inEqual forces on an object in
opposite directions are calledopposite directions are called
This does not change anThis does not change an
objectobject’s motion.’s motion.