Newton's Law of Motion - First, Second & Third - Physics

in this video we're going to talk about

Newton's law of motion and there's three

laws that we're going to go over let's

talk about the first law so what exactly

does Newton's First Law of Motion

state well one part States this an

object at rest will remain at rest

unless acted on by a

force particularly in our imbalance

Force so let's say if we have a surface

and if there's a box on its

surface if we don't apply a force this

box will not move all the forces that

are currently acting on this

box cancel they're balanced forces for

example you have the weight force of the

Box let's say the box has a mass of 10

kg to calculate the weight Force it's

equal to M *

g m is the mass in kilogram G is the

gravitational acceleration

so m is 10

kg

G is 9.8 m per second squ that is the

acceleration due to gravity so the

weight force is simply 10 * 9.8 so it's

equal to 98

Newtons gravity exerts a downward weight

force on any

object now the block is not accelerating

downward it's at rest so the must be

some other force that keeps it at rest

the force that the ground exerts on a

box is known as the normal force and it

has to balance the weight force in order

to keep the block where it is and so the

normal force is also

98 so as you can see these are balanced

forces the net force on his box is equal

to zero and so it remains at

rest unless we apply an unbalance

Force then the block May begin to

move we may have to overcome static

friction but if we apply Force then it

can move so an object at rest will

remain at rest unless acted on by net

force so that's the first part of

Newton's uh first law of

motion now what about the second part of

it Newton's Second Law also states that

an object in motion will continue in

motion unless acted on by a net

force it's basically a statement of the

law of inertia now let's think about

this let's say if we have a

surface with let's say it's a rough

surface let's use a carpet for

example if you try to roll a ball on a

carpet for the most part the ball is

going to quickly come to a stop it's not

going to move very far and the reason

why that happens even though this object

is in motion

there's a lot of friction between the

surface of the ball and the carpet and

friction opposes motion and so because

there's a net force this object will not

continue in motion it's going to come to

rest and that's what we see in real life

if you roll a ball eventually comes to a

stop it doesn't continue forever but

Newton's first law of motion states that

an object in motion will continue in

motion unless acted on by force now if

you think about it what will happen if

we can get rid of friction will the

object continue to move

forever now imagine if you have a smooth

surface let's say like

ice now if we take a puck and slide it

across the ice it's going to move for a

very very large distance it's not going

to come to rest like the ball on the

carpet the ball on the carpet is going

to stop after a very short distance but

this Puck is going to slide across the

ice for a long

time now let's say if we use a ball and

we roll it on

ice let's say if you put it on a frozen

lake and you roll it across the lake

it's going to roll for a very very long

time

until it comes to rest it's going to

take a long time for it to come to rest

now why is

that why is it that if we roll a ball on

a rough surface it's it takes a very

short time to come to rest it comes to

stop it comes to a stop quickly but if

you take a ball and put it on an icy

surface it will roll for a longer time

the reason for that is because there's

more friction between a ball and a rough

carpet but between the ball and the icy

surface there's less friction and so

because there's less friction this ball

will continue to travel for a much

longer time now what's going to happen

if we can complete completely get rid of

friction will the object continue to

move

forever think about it now keep this in

mind even though there's very little

friction between the icy surface and the

ball you also have air resistance as the

ball is moving

forward the air molecules can slow it

down so you have air resistance and if

it's moving fast this can be a Air drag

as

well but where can we find a place where

there's virtually no

friction the best place where there's

almost no friction is outer space in

outer space there's virtually no air

it's almost non-existing you might have

a few molecules here and there but for

the most part the pressure is extremely

extremely

low if you think about

it we know that the Earth revolves

around the Sun and the Earth is an

object in motion

and the Earth has been revolving around

the Sun for a very very very long time

Millions perhaps billions of years and

it continues to keep

moving and it makes sense because in

space there's virtually no

friction it's not enough to slow the

Earth down and so it continues to move

in its

orbit and thus we can see Newton's first

law of motion in action here an object

in motion will continue in motion unless

acted on by a net unbalanced

force now you might be wondering all of

this information is great but how can I

apply this information in a problem How

will I see a question on a test

well there's some things that you need

to know if an object remains at rest the

net force aced on the object is equal to

zero make sure you understand that

concept the second thing is if an object

is in motion let's say if it's moving

with constant

velocity then the net force acting on

that object is equal to zero make sure

you understand

that if the net force is not

zero then there is a net

acceleration but when the net force is

zero the acceleration in that direction

is also equal to zero which means that

the velocity is constant keep in mind

acceleration is defined as the change in

velocity that is the final velocity

minus the initial velocity divided by

the change in

time so at constant

velocity VF and V will be the same if

you take a number and subtract it by the

same number you're going to get zero so

in constant velocity VF minus V is 0 0/

t is0 now according to Newton SE law the

net

force is equal to the product of the

mass and the

acceleration so if the acceleration is

constant and if you increase the mass of

the object the net force will increase

so the net force is proportional to the

mass of the object now let's say if you

keep the mass constant and if you

increase the magnitude of the

acceleration the net force will increase

as well so the net force is also

directly proportional to the

acceleration now what if we keep the net

force constant what is the relationship

between the mass and the

acceleration if you increase the mass

the acceleration will decrease provided

if the force Remains the Same if you

decrease the mass the acceleration will

increase under constant force

conditions now let's put some numbers to

it if you you double the mass while