ten nine eight we have a go for main
engine start we have main engine start
four three two one
bill and liftoff liftoff of the space
shuttle and it has cleared the tower
discover a performance nominal Roger
how's the picture cover back Kevin great
picture hello and welcome to the flight
deck of discovery or 260 kilometres
above the surface of the earth traveling
at 8 kilometers per second if I look out
the window I can see a light nice to you
huh what's this
hey macadamia nut must be lunch
banana pudding this must be dessert one
of the fun things about flying in space
is that things float that's because we
are in a freefall orbit about the earth
the Space Shuttle Orbiter myself the nut
and my pudding are all falling together
we're weightless soft this can of
pudding is weightless why did it hurt
and hit my head the answer to this
question requires a little research Wow
let's imagine that I can send this nut
and this can down to a laboratory on
earth some catch
as you can see the can of pudding weighs
100 times more than that but weight can
be confusing because weight depends on
where you do the weighing on the moon
the nut and the can weigh only 1/6 of
what they do here on earth and here in
orbit they both weigh the same zero so
why is that it's because weight depends
upon the gravitational pull exerted on
objects the earth is very big so its
gravitational pull is very strong the
moon is much smaller so its
gravitational pull is weak and objects
weigh much less here on earth were in
freefall and that makes it seem like
there's no gravity at all so objects
have different weight depending upon
where they are well then what does that
have to do with the bump on my head the
answer lies in the fact that even though
the pudding can has no weight it does
have mass mass is that not a matter that
is packed into an object all objects in
the universe have mass weight can change
but not mass the mass of this nut and of
this pudding can remains the same no
matter where they are in the universe
even here on the orbiter the can of
pudding has more mass in the nut so it
hit me with more force so why have we
spent all this time explaining mass to
you well it's because you have to
understand the concept of mass in order
to understand Sir Isaac Newton's three
laws of motion and that is what this
show is really all about
Nik was a pretty smart guy about 300
years ago he came up with the first
mathematical formulas to describe things
in motion
we couldn't have traveled up here into
space without a good understanding of
Newton's three laws of motion so what's
the first law every material object
continues in its state of rest or
uniform motion in a straight line unless
it is compelled to change that state by
force is impressed upon it can we come
up with a simpler way to say that an
object at rest will remain at rest
unless acted upon by an unbalanced force
and an object in motion will remain in
motion unless acted upon by an
unbalanced force thanks professor aster
that's much clearer you're welcome
now for a demonstration here's the can
of pudding
it's at rest because it hasn't had any
force applied to it so let's apply some
force now our objects in motion and it
will stay in motion at a constant speed
in a straight line until it's acted on
by an unbalanced force like a head don't
try this at home
now on to the second law it explains the
relationship between course mass and
acceleration force is a push or a pump
and we already know about mass
acceleration is how fast an object
changes its speed here's our can again
we'll use this little air puffer to
apply a gentle force to it for a short
time see it doesn't accelerate very much
now we'll apply a greater force that did
it it really accelerated that time the
greater the force are greater the cans
acceleration but how does mass come in
the mass of an object affects how fast
it will accelerate when a force is
applied if you apply an equal amount of
force to two objects the object with the
most mass accelerates the least
here are two cans of pudding tapioca and
butterscotch if we apply the same force
to both cans they should both accelerate
the same and travel at the same rate of
speed right let's try
what happened one can seems to have
accelerated more was Isaac Newton wrong
wait here's the problem someone eats
putting out of one of these cans without
putting in the can the can has last
class and thus it accelerates more
Newton explained that force and mass are
related to each other by acceleration a
force is a push or a pull on the cam
more force gives more acceleration mass
resist acceleration if we gave the same
push to two objects the one with less
mass will accelerate more so here's our
equation on top of the empty can and
below the full force equals mass times
acceleration so Newton wasn't wrong too
late my pudding now what about Newton's
third law of motion for every action
there is an equal and opposite reaction
well that's very easy to show up here in
space what happens when Lacey pushes
against Greg the force on each astronaut
is equal and opposite so they go off in
opposite directions at the same speed
but once again mass plays a role in it
all let's try that again but this time
let's make it two against one the two
crew members on the right have more maps
together than our crew member on the
left but the force is still equal when
they push off of each other what do you
think will happen now well you're right
Lacey really goes sailing through the
midday let's do that again this time in
slow motion
Lacey has less mass than the other two
crew members Don and Greg and therefore
he has a greater acceleration and
travels faster let's run through these
three laws of motion again an object at
rest remain
at rest unless acted upon by an
unbalanced force and an object in motion
will remain in motion at the same speed
in the same direction unless acted upon
by an unbalanced force the acceleration
of an object depends upon its mass and
the size of the force applied to it and
for every action there is an equal and
opposite reaction Newton's three laws of
motion are not just formulas or words on
paper they're all around us and
everything we do
you