Gravitation | Weight of an Object on Moon - Mass and Weight | Class 9 | Science | BYJU'S
Summary
TLDRThis educational video script explores the nuanced differences between mass and weight, clarifying common misconceptions. It explains that mass, measured in kilograms, is the total amount of matter in an object, while weight, measured in Newtons, is the force exerted by gravity on that mass. The script corrects the common mistake of equating mass with weight by discussing how weighing scales actually measure weight but display it as mass. It also delves into how weight varies with gravity at different locations, such as the poles versus the equator and on other celestial bodies like the Moon. The video aims to provide a clear, concise understanding of these fundamental concepts.
Takeaways
- đ Mass is the total quantity of matter in an object, whereas weight is the force of attraction between the Earth and the object.
- đ People commonly confuse mass and weight because they are often asked for their weight, which is actually their mass.
- đ Weighing machines measure weight, but they display the mass by performing an internal calculation using the acceleration due to gravity (G).
- đ The weight of an object varies depending on its location, such as at the poles or the equator, due to differences in gravitational acceleration.
- đ At the poles, where the radius of the Earth is smaller, the gravitational acceleration is higher, resulting in a higher weight compared to the equator.
- đ At the center of the Earth, the net gravitational force on an object is zero, making the weight zero, despite the presence of mass.
- đđ The weight on the Moon is approximately one-sixth of the weight on Earth due to the Moon's lower gravitational acceleration.
- đĄ Weightlessness is experienced during free fall because the force acting on a freely falling object is zero, as seen with a ball inside a dropped plastic glass.
- đïžââïž A person can lift six times more mass on the Moon than on Earth because the gravitational force on the Moon is one-sixth that of Earth.
- đ The concept of 'Concept Bytes' is introduced as a short, crisp, and clear way to learn and understand complex concepts quickly.
Q & A
What is the difference between mass and weight?
-Mass is the total quantity of matter in an object, measured in kilograms (kg), while weight is the force exerted on an object due to gravity, measured in Newtons (N).
Why do we often confuse mass and weight?
-We often confuse mass and weight because when asked about our weight, we tend to answer in kilograms, which is actually a measure of mass. This confusion arises because weighing machines measure weight but display the reading as if it were mass.
How does the weight of an object vary at different locations on Earth?
-The weight of an object varies depending on the location due to differences in the acceleration due to gravity (g). At the equator, the value of g is less due to Earth's larger radius, while at the poles, g is higher, making the weight greater.
What does a weighing machine actually measure?
-A weighing machine measures the force of gravity acting on an object, which is the weight. It then internally calculates and displays the mass by dividing the measured weight by the local acceleration due to gravity.
What is the relationship between weight and the acceleration due to gravity?
-Weight is calculated as the product of mass and the acceleration due to gravity (W = m * g). Therefore, weight depends on the local value of g, which can vary with location.
Why does the weight of an object become zero when it is in free fall?
-When an object is in free fall, it experiences weightlessness because the only force acting on it is gravity, which provides the acceleration needed for free fall. There is no net force acting on the object in the direction of the weighing device, hence the reading is zero.
What is the weight of an object at the center of the Earth?
-At the center of the Earth, the net force acting on an object is zero because the gravitational pull from all directions cancels out. Therefore, the weight of an object at the center of the Earth is zero.
How does the acceleration due to gravity on the Moon compare to that on Earth?
-The acceleration due to gravity on the Moon is approximately one-sixth of that on Earth, which means an object's weight on the Moon would be one-sixth of its weight on Earth.
If Rahul can lift a maximum of 30 kg on Earth, how much can he lift on the Moon?
-Rahul can lift a maximum of 180 kg on the Moon because the Moon's gravity is one-sixth of Earth's. The force he can apply remains the same, but it can support a greater mass due to the reduced gravitational pull.
What would happen to the weight of a gold bar if Amit buys it at the poles and gives it to his friend at the equator?
-The weight of the gold bar would decrease when moved from the poles to the equator because the acceleration due to gravity is less at the equator. However, the mass of the gold bar remains constant regardless of location.
Outlines
đ Understanding Mass vs. Weight
The paragraph introduces the common confusion between mass and weight. It explains that while mass is the total quantity of matter in an object, weight is the force of attraction between the Earth and the object. The script clarifies that weighing machines measure weight, not mass, and they provide a mass reading by performing an internal calculation based on the gravitational force. The distinction is important because mass remains constant regardless of location, whereas weight varies with the acceleration due to gravity (G), which changes depending on the location on Earth or other celestial bodies.
đ Gravity's Effect on Weight
This paragraph delves into how the value of gravitational acceleration (G) affects weight. It discusses the variation in G at different points on Earth, such as the equator and the poles, due to the Earth's shape. The script explains that the force of gravity, and consequently weight, is less at the equator and more at the poles. It also touches on the concept of weightlessness during free fall, where an object in free fall experiences zero weight as there is no net force acting on it. The paragraph concludes with a problem-solving example involving spring balances and the weight of an object in different states of motion.
đ Weight on the Moon and Misconceptions
The final paragraph addresses the misconception that weight is greatest at the center of the Earth. It explains that at the center, the net force due to gravity from all directions cancels out, resulting in zero weight. The discussion then shifts to the Moon, where the acceleration due to gravity is one-sixth that of Earth's. A practical example is given to illustrate how much more mass a person could lift on the Moon compared to Earth, given the same force applied. The paragraph ends with a homework question about the weight of gold at different locations on Earth, hinting at the variation in weight due to changes in gravitational acceleration.
Mindmap
Keywords
đĄMass
đĄWeight
đĄAcceleration due to gravity (G)
đĄWeighing Machines
đĄEquator
đĄPoles
đĄFree Fall
đĄWeightlessness
đĄCenter of the Earth
đĄMoon
đĄGold
Highlights
Definition of mass as the total quantity of matter.
Definition of weight as the force of attraction between Earth and a body.
Weighing machines measure weight and calculate mass through internal calculations.
Weight varies at different locations on Earth due to differences in gravitational acceleration.
At the equator, the value of gravitational acceleration (g) is less, resulting in a lower weight.
At the poles, the value of g is higher, resulting in a higher weight.
Mass remains constant regardless of location, while weight changes with gravitational acceleration.
Weightlessness is experienced during free fall as the force of gravity is balanced by the acceleration of the body.
At the center of the Earth, the net gravitational force is zero, resulting in zero weight.
On the Moon, the acceleration due to gravity is one-sixth of Earth's, making weight six times less.
Rahul can lift six times more mass on the Moon due to its lower gravitational acceleration.
The misconception that weight is maximum at the center of the Earth is debunked.
The formula for weight is mass times gravitational acceleration (W = mg).
The SI unit for mass is kilograms (kg), while for weight, it is Newtons (N).
A weight of 100 Newtons attached to two spring balances will show different readings depending on whether they are at rest or in free fall.
Amit's friend will not agree with the weight of the gold bot at the equator due to the difference in gravitational acceleration.
The concept of 'Concept Bytes' is introduced as a short, crisp, and clear way of learning.
Transcripts
[Music]
foreign
let me ask you something what is the
difference between mass and weight I
know the first time you hear this
question you feel like what kind of
silly question is this mass is mass is
the total quantity of matter where it is
weight it's the force
but let me tell you from where this
confusion starts what if somebody asked
you what's your weight what do you
answer
40 kg 30 kg 50 kg
you answer in kgs right
if you also have this confusion what do
weighing machines measure what do they
tell you is it mass is it weight welcome
to the short under 10 minute session we
call as the concept bytes in today's
session I'll tell you the exact
difference between mass and weight what
do the weighing machines tell you what
is it I'll tell you that and apart from
that we'll discuss everything about wage
how the weight varies at different
different positions if you go inside the
earth if you go different planets if you
go to the Moon right we'll solve some
questions nice short crisp and clear
that's what we call as concert bytes
welcome if you know what we do press the
like button because this video is going
to be awesome all right let's start
so if somebody asks you do mass and
weight refer to the same thing so let's
say this person he's saying now I'm fit
my weight is showing 70 kg she say 70 is
not your weight here it's your mass
so why do we always answer in kgs
let me tell you exact difference between
mass and weight see we all know this
mass is the total quantity of matter
right how much of matter what is matter
molecules atoms whatever it is
what is it made up of total quantity of
matter is called as the mass all right
what is weight weight is the force of
attraction right it is the force of
attraction between Earth and the body at
least on Earth we are talking about or
the planet could be right between any
planet or any Heavenly Body and the
masses
that is your weight right and what is
your mass it is the total quantity of
matter in you correct so and the mass it
does not depend on G Master total
quantity of matter is
so it does not depend on G which means
it does not depend on acceleration due
to gravity but weight depends on G why
weight is mass into acceleration due to
gravity this formula is not different it
is f equals m a only weight is the force
force force equals mass into its
acceleration on Earth we call the force
as weight we call as acceleration
gravitational acceleration to gravity
and I have cable term so w equals mg
that's how this formula came with same
formula right so it depends on G mass is
in kgs right its s i unit is kgs but
weight being Force has the s i unit of
force which is Newton it always remains
constant mass does not change by you
know mass is not changed until unless
you start moving the speed of light
it varies from place to place right
weight varies from place to place and
yes it does
it can never be zero Mass cannot be zero
it can be zero at the center of the
earth what
I'll tell you what and why this
misconception comes I'll tell you that
so no
let's do this first question rho anyway
600 Newton at a point near the equator
if she measures her weight at the North
Pole her weight will
come on we have done this we have done
this
if she measures her weight at North Pole
her weight will compare to 600 Newton
which is measured at equator
well
W equals m into G right now the value of
G is an average value of 9.8 but we have
learned this that on the equator the
distance of the body from the center is
more why because the radius of Earth
equator is more Earth is not a perfect
circle it's a geoid shape right so at
the Equator the radius is more compared
to the poles now what is g g equals g m
upon R square if this radius is more G
will be less so at Equator the value of
acceleration due to gravity is less
means the weight is going to be less at
the poles the value of G is going to be
moved that is acceleration due to
gravity is going to be more it is about
9.83 means your weight will be more if
you want to lose weight and you live
near poles come to Equator your weight
will be you know less all right okay so
weight is M into G and G is remember R
square which means at the Equator the
value of G is less polar radius is less
than equatorial radius so her weight
will be more if she goes to the pole why
because value of G is more at the post
right so her weight will in increase
Mass into G at poles is going to be more
than Mass into GF equator okay fine now
let me come back to the initial question
if mass is different and weight is
different then what is it that the
weighing machines measure
weighing machines they measure your
weight only
they measure your weight only yes but
what else
they tell you the value of the mass by
doing internal calculation by if think
about it m into G if somebody measures
and you divide it with G what it becomes
it becomes Mass right so they answer it
like Mass but they actually measure mass
into G right mg if I go to class 11 I
would probably end up saying they
measure the normal force but right now
I'm just telling you okay they measure
your weight only they measure your
weight but they divide it with the value
of G to give you their Mass so they are
answering in terms of mass but they are
measuring weight right clear fine okay
a weight of 100 Newton is attached to
the end of two spring balances A and B
the spring balance a is attached to
ceiling and B is allowed to fall freely
find the readings of A and B
respectively
B is in free fall and a is hanging
nicely spring balances can tell you what
is the force right if you hang a hundred
Newton if you know the answer come on
think about it pause the video think
about it and then cross checker
weight of 100 Newton attached to the end
of two spring balances by a is at rest
we all know if I take a spring balance I
keep it at rest and hang a mass it will
read the weight of the mass right so a
should be 100 Newton we all know that
what about B
what do you think will be measure and B
is really falling
have you noticed whenever you fall
freely
we say it is weightlessness Hannah
correct you feel weightlessness when you
fall right correct so with the same
logic you can say when a body is freely
falling it weights becomes zero its
weight becomes zero means the force
becomes zero means the spring balance
will read zero you can try it you can
try this one it's very easy you know you
can take a bottle you can uh or you can
say take a glass
which class would you say take a plastic
glass take a plastic glass and put a
ball inside it and you drop it you will
see the ball will remain at its position
okay fine so it will be 100 Newton and
zero so when a body falls it experiences
weightlessness if a body falls freely
means with the acceleration due to
gravity the weight becomes zero correct
fine but yeah so it is 100 and 0 Newton
now let me ask you what is the weight at
the center of foreign
but let me tell you people don't believe
that a lot of people have this confusion
why
listen weight equals m into g means M
into g m by r
square right
M into g m by R square correct answer
if radius at equator is more the value
of G is less if the radius at pole is
less the value of G is more agreed by
pole pay radius
what is g acceleration due to gravity
you know
if we take the body inside the earth
means the value of G will be even lesser
does it mean the weight will be even
more which means if I take the body to
the center means radius is 0 weight
would be infinite is it no
first of all why was this Force
occurring because the mass was pulling
you know because of the force of
gravitational
foreign
imagine you are at the center and from
all the directions people are pulling
you with the Rope okay imagine this
scenario okay you are standing at the
center and from every direction
you are being pulled by a rope okay you
are being pulled in each and every
direction by a rope
what is the net force on you think about
it come on what is the net force on you
zero why because you are being pulled
from every direction
correct so what is happening when you're
at the center of the earth the mass of
the Earth around this body is pulling
this body in all the directions in all
the direction it is being pulled so net
force becomes zero if Force becomes zero
weight becomes zero so that is why
we always think that we feel maximum
weight at the center of Earth but it's a
misconception actually wait at the
center of Earth is zero clear it's a
very important very basic question but
very commonly occurring questions okay a
weight on the moon
acceleration to gravity of the Moon I
gave you this homework in a previous
video if you remember I think you might
have solved it right so
the gravity the acceleration due to
gravity on moon is G by 6.
means the weight will be weight of the
earth divided by 6 correct if G is 1 by
6 weight will also be one by six now
six times weaker right so G Dash is the
acceleration of gravity on the moon and
G is the action derivative of Earth so
acceleration due to gravity on the moon
GM is equal to 1.6 meter per second
Square do you have to remember the value
no but 1 by 6 is something I want you to
remember okay
so let's do a very quick question the
maximum mass that Rahul can lift on the
earth is 30 kg what will be the maximum
mass that he can lift on the moon
and you apply the same John the same
Force how much mass can he lift that is
the question if you know the answer or
if you can solve this question pause it
and solve it otherwise cross check
Ticket listen to me I told you
Rahul has the same amount of force he
can apply so on Earth how much force is
he applying on Earth he is applying
Force which is the weight of the body W
is equal to 30 into
G of earth right okay when he goes to
Moon he can apply the same Force huh
okay so he is applying Force which is 30
into GE and it will be equal to how much
mass he can lift multiplied by the
acceleration to gravity on the moon
what have I done
I have equated the force the force he
can apply on Earth is equal to the force
he can apply on moon right correct
is equal to how much mass correct or you
can say the force he is applying is
equal to how much of the weight weight
so 30 into G is equal to M into g m so I
can say 30 into GE is equal to M into g
e By 6 y because G of moon is equal to 1
by 6 of G of Earth so G is a g e cancel
mass will be 30 into 6 is equal to
180 kgs so on moon he can lift 1 80 kgs
six times
if imagine imagine right if on Earth
the gravity is more means you can lift a
small Mass but you have that much force
right and that much force will be equal
to a greater mass on moon the moon's
gravity is 1 6 means you can lift any
Mass which is six times heavier on the
moon henna take it fine clear so that's
why 180 kgs becomes the correct answer
all right ah a small homework question
for all of you Amit buys few grams of
gold at the poles as per the instruction
of one of his friends he hands over the
same when he meets him at the equator
will the friend agree with the height of
gold bot sorry weight of the gold bot if
not why it's your ncert equation by the
way come on if you know the answer tell
me in the comment section otherwise
others will
give you the answer all right everybody
with this I want all of you to try this
question tell me in the comment section
and I hope you like this short crisp and
clear way of learning because as the
concept bites we'll do live questions
we'll do practice questions a lot but
this is a time saving way I want all of
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don't forget and see you next time take
care bye
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