FORCE and PRESSURE Part 1 – Physics Class 8th CBSE #1

FORCE and PRESSURE Part 1 – Physics Class 8th CBSE #1


In this video we learn about Force. “There’s so much happening in these video
clips and would you believe that there’s not one thing thats not directly related to
the topic of force in your text book. And the thing is,stuff like this is happening
all around you all the time and that’s the same physics that you are studying in your
school curriculum.” “all the video clips that you just saw will
cover all these topics from your text book” What is force? What Causes Force? What is Magnitude and What is the Unit of
Force? What is Direction of Force? What are the Effects of Force? What are the Types of Force? So let’s start with the Definition of Force
and then we will explore what it means. A force is a push or pull upon an object resulting
from the object’s interaction with another object. so what are the main things in this definition. There need to be two objects. There needs to be an interaction between them. Here are two objects…is there an interaction
between them? no! so theres no force from that point of
view. …now you can see the car moving
…now you can see the car moving again So both Pushing and pulling there is Force
due to the interaction between the two objects, man and the car
Here are some everyday activities we can see where force is in action
Pushing, Pulling, Lifting, Stretching, Twisting and Pressing. So now we know that force requires an interaction
between two objects. whenever there is an interaction between two
objects, there is a force applied on both objects. When the interaction ceases, the two objects
no longer experience the force. But let’s see another situation. Here, man is pushing the car, applying a lot
of force, but why is the car not moving! Does that mean that there is no force being
applied? There is Force, but to understand it, we need
to introduce the next point. A force is a vector quantity, and that means. Force has Magnitude and Direction
In general terms, Magnitude loosely means how large something is and Direction means,
where it is going. Therefore the strength of Force is expressed
by it Magnitude. The SI unit to measure this magnitude of Force
is called Newton, in short, it’s written as N
Force is equal to mass into acceleration. So capital F is for force, M is for mass and
A is for Acceleration. The metric units of mass are kilograms and
metric units for acceleration are meters per second squared. Force is Kilograms per meters per second squared. 1N is the amount of force required to give
a 1kg mass an acceleration of 1m/s2 To say 10 Newton of force we can write “10
N” When 2 forces act on an object, 2 main things
can happen because, either the forces act in the same direction, or the forces act in
opposite directions. These two situation can give rise to a total
of 3 situations, because Both Forces act in same direction. Both Forces act in opposite direction but
they are of unequal magnitude or Both Forces act in opposite direction and
they are of equal magnitude What happens if the Forces are in the Same
direction… The resultant force on the box is equal to
the sum of the two forces. On other words, when two forces act in the
same direction, their effective magnitude increases. So if person one applies 400N and person two
applies 400N, then the resultant force is 800N… What happens if the Forces are unequal and
act in the opposite direction? If the two unequal forces are applied in the
opposite direction, the net force acting on the object is equal to the difference between
the forces. So here one person is pushing with 800N and
the other person with 400N, the net force will be 400N in the first persons favour,
and the box will move in the direction where the first person is pushing it. What happens if the Forces are equal and act
in the opposite direction? Since we have already seen that the net force
acting on the object is equal to the difference between the forces, and here they are equal
in magnitude, so the net force acting on the object is ZERO. So here person 1 is pushing with 800N and
2 people are pushing from the opposite direction with 400N each, the net force is going to
be? You’re right, ZERO. So the box will not move anywhere. The same thing happens most of the time in
a tug of war. Mostly, the magnitude of pulling force that
a big group of people can put on the rope is almost the same as another group and thats
why generally the tug of war takes a long time to move. Lets see here how it works. Here each group is going to pull against the
tree, and the spring balance will show us whether the force is similar to each other
or not. There, both are almost identical. So now lets go back to the point where i asked,
why is the car not moving if there is force being applied? and i can show using the weighing
scale that he is applying force because the scale has moved quite a but, but then why
isn’t the car moving? The thing we don’t realise here is that the
car is applying a large force on the ground due to its weight, and the ground is applying
the same force back to keep it in place, and the system is in balance. This man doesn’t have to worry about the balanced
forces but still has to overcome the frictional forces. So lets keep adding to the force and then
the car will eventually start moving. There, as a second person joined in, the additional
force got the car to start moving. The Direction of Force is shown by Arrows
and the generally the length of the arrows in the drawing show if the magnitude is same
or different from the other forces shown in the same drawing. These are called free body diagrams where
the forces are shown with their direction and magnitude. So we have already understood What is force,
how is it caused, how is measured. Now lets see what are The effects of Force
since Force can’t really be seen, it can only be judged by the effects it can produce in
the objects around us. 1-Force can move a stationery object
2-Force can stop a moving object 3-Force can change the speed of a moving object
4-Force can change the direction of a moving object
The above 4 points confirm that Force can change the State of Motion, the “state”
describes the speed and direction of the motion 5-Force can change the shape of an object. After heading the ball, look at his face,
don’t you think the shape is changed? This is just for fun. So now lets see what are the different types
of forces We know that forces can be exerted only when
objects interact with each other, but interestingly, they can interact whether they are in contact
with each other, or even if they are not in contact with each other. Therefore the Types of Forces can be broadly
classified into 2 categories, Contact force and Non-Contact forces. A-Contact Forces -act only when the interacting
objects are in contact with each other. B-Non-contact Forces – can act even when the
objects are not in contact with each other. Under contact forces, first is the Muscular
Force, that is the force exerted by the muscles in the body, in humans or animals. This includes almost everything we do
2nd is the Frictional Force or Friction, this is the resistance to motion of one object
moving relative to another, while both are in contact. So why doesn’t the ball keep rolling forever
and why does it roll more on the smooth ground that on the rough or the rocky ground. Thats because friction applies a force on
the ball thats opposite to the direction of the motion. In the flat ground there is less friction,
so it moves a lot more distance than the rough or the rocky ground. To show this we had made a simple thing so
that we don’t push the ball with difference forces. so that the ball can roll off with the same
speed. Friction is a necessary evil, without it we
wont be able to run or walk. A Match lighting up is good example of friction
coming into action 3rd is Normal Force . the book lying on the
table, even though it seems that there is no forces acting here, but think about it,
gravity is pulling the book down and An opposing force is still acting on the book to keep
it in place. This force is the ‘normal force’. this
is the support force exerted upon an object that is in contact with another stable object,
which is the table here. A normal force can also be horizontal. Example is if you lean against a wall. you are the object, wall is the stable object
that provides the support force. 4th is the Air Resistance Force and it’s
a special type of frictional force that acts upon objects as they travel through the air. To show this, here a person will run with
the umbrella closed and then he runs with the umbrella open to increase the air resistance. You can see the stress on his face, if you
don’t believe it, you can also try this yourself. 5th is the Tension Force this is the force
that is transmitted through a string, rope, cable or wire when it is pulled tight by forces
acting from opposite ends. 6th is the Spring Force, this is the force
exerted by a compressed or stretched spring upon any object that is attached to it. Here are some examples of spring forces. 7th is Applied Force, this is a force that
is applied to an object by a person or another object. Before we move on to non contact forces, if
we look at pushing the car again, do note that once the object starts moving due to
an applied force, if there was no friction or air resistance, it would keep moving without
any force required. But it would remain at that constant speed
and then to increase or decrease the speed, or even stop it, again some external force
would be required. Now we’ll look at non-contact forces. These are the kinds of force that can be exerted
by one object on another object, even from a distance, therefore These forces can act
even when the objects are not in contact with each other. 1st is Magnetic Force is the force exerted
by a magnet. A magnet can exert this force without actual
contact on iron and on other magnets. It can only attract or pull the iron/ferrous
object. But with other magnets, it can attract as
well as repel which means, it can pull or even push the other magnet, all without any
physical contact. 2nd is Electrostatic Force is the types of
forces exerted by all electrically charged bodies on other charged bodies in the universe. These forces can be both attractive and repulsive
in nature based on the charge of the bodies, which either be a positive or negative charge. Electric Charges can be produced by friction
when one object is rubbed over another one. This electrically charged object is said to
have a “stationery electric charge” or an “electrostatic charge” also known as
“static electricity”. The force exerted by an electrically charged
object is called an electrostatic force, So combing through hair and rubbing the balloon
cause them to be electro statically charged and when they are brought close to paper or
another balloon they will exert an electrostatic force on them. If one balloon is charged and the other is
not charged then they will attract each other as they have opposite charges. If the other ballon is also charged, then
it will repel as both balloons are similarly charged 3rd is Gravitational Force is the pull exerted
by objects possessing mass. it is the force with which the sun, earth,
moon, or other massively large object attract one another. The gravitational force between the Sun and
earth holds the earth in orbit, and similarly between earth and moon holds the moon in orbit. And without the gravitational force holding
these bodies together, the moon would simply float away from the earth and similarly the
earth would leave the orbit of the sun. The force with which the earth pulls all objects
towards it, is called the force of gravity, or just Gravity. All objects on earth experience this force
that is directed “downward” towards the center of the earth. The force of gravity on earth is always equal
to the weight of the object. You cant cheat gravity but you can cheat the
mind’s perception of gravity..:) Im doing it here, but this is a different
topic that we’ll talk about some other time. A simple example of gravity is, that a ball
thrown up would keep going up but then because of gravitational force acting against the
motion, first it slows down the ball till it stops in the air and then it reverses the
direction and it comes back towards the ground, this reversal and coming back to the ground,
happens because of gravity. With this we have covered the topic of force,
so lets Recap. We explored. FORCE
It’s a push or pull on an object most important is interaction between two
objects The SI unit to measure this magnitude of force
is called Newton In short it is written as capital N
1 Newton is the amount of force required to give 1 kg mass an acceleration of 1 meter
per second squared. Direction of Force
Forces can be in same direction or opposite direction
If they are in same direction, the net force is equal to the vector sum of the two forces
If its in opposite direction, the net force is equal to difference of the forces
in the direction of the bigger force Effects of force
Force can move a stationery object Force can stop a moving object
Force can change the speed of a moving object Force can change the direction of a moving
object Force can change the shape of an object Types of Forces – Contact Forces
Muscular Force Frictional Force or Friction
Normal Force Air Resistance Force
Tension Force Spring Force
Applied Force In Non-Contact Forces we have
Magnetic Force Electrostatic Force
Gravitational Force Here’s one last look at the subtopics again
and then we’ll move on to the TIY of the lesson. After this is the TIY you can do as a school
project thats related to this topic. After the TIY, you can go to the next lesson. T.I.Y for force. So I was wondering what Sub-topic to choose
to make a TIY project for this Topic of FORCE. I thought maybe it would be good to show the
EFFECTS of force….so the question is, what can we make or do that has all the elements
of Effects of force…we need something that hits a stationery object…something that
deflects and all the other points under effects of force…i thought for a little time about
what we can do, and suddenly then a game came to mind. “Carrom”. Now please note one thing, normally in my
videos i will be making things to show TIY projects, but in this first video, i didn’t
have to make much because you’ll see that the idea itself was good enough to explain
almost everything. So think about it, how can carrom show… Effects of force
Force can move a stationery object. It’s easy to show that force can move a
stationery object. And in the same one you can see that Force
stopped a moving object Force can change the speed of a moving object
– see striker hits the front wall and slows down a bit, but you cant see the change much,
so how do we slow down the bounce so that you can clearly see it? think about it…the
board is made of hard wood so that it bounces well..so how do we slow it down? by putting
something soft…lets see. I’m adding a small strip of rubber with a
double sided tape. Lets see if it slows it down after the bounce…it
does look like it slowed it down a bit, but we need to slow it down a little more. Maybe something even softer, like Foam. Now lets try with foam stuck with double sided
tape to the front wall. YES, thats so much better. Force can change the direction of a moving
object – thats easy, the striker hits the side wall, the wall applies a force and the
striker changes direction and bounces back. Force can change the shape of an object – now
this was tough…i thought about it quite a bit but then i realised that once again,
to change the shape, i need to think of a material that can stay in its changed shape
so that you can show it to others if you do it as a project. What is a soft material that changes shape
and stays in new shape with force?Soft clay, plastercine. Yes. let’s make a coin with it, and try it out
and see if it works. There, it works
You can see that it flattened from the side where it hit the wall as well as the striker. So with carrom we managed to show all the
effects of force. But then can it also be used to show The TYPES
of forces? Lets try the Contact Forces first. Muscular Force – thats easy, finger has muscles
and its hitting the striker, so muscular force is applied
Frictional Force or Friction – thats also easy and those who play carrom do it regularly
regularly. See when the striker is not moving smoothly
because of friction then powder is sprinkled on the board to reduce the frictional forces
acting against the striker and the coins. And see, on the Left i will hit without the
powder, and on the right i will hit with the powder on the board…now the important thing
is to be sure that the force I’m going to use is the same, For that i have made a striker
launcher. Lets try it with that. There, you can see that the striker travelled
much more where i added powder to reduce friction. Normal Force. The coin resting on the board is good enough,
think about it I’ve explained it earlier. Air Resistance Force. Now this is difficult to show because the
striker and coin are very small, so the air resistance will be too small for us to see. So we need something thats big enough that
will cause a lot of air resistance so that you can see it. Now what can that be? Did someone say “use the board” itself? I love the idea…so lets see if the board
can be used to show that wind resistance is a force that effects motion…lets carry it
on a cycle…when we carry it like this, its easier to cycle, as compared to when you carry
it like this. You have to believe me on this or judge by
the effort he is putting to cycle forward. Tension Force. After all that exercise, he has left the cycle
and is dragging the board on the ground with a rope, thats good enough to show the tension
forces through the rope Spring Force. My DIY carrom striker launcher doesn’t have
a spring but has a rubber band which does the same job. So thats a good example of spring force. The DIY of the carrom’s striker launcher
can be seen in the videos of d’art of science. Applied Force lifting the board to take out
the coins and moving all the coins and settling them in position, is all applied force. Almost anything you do is applied force. If we could show all these aspects of force
using the carrom, then why not even Non-contact forces? Lets try and do it. Non-Contact Forces
Magnetic Force. for magnetic force we need magnets. For this so might as well get round/Donut
magnets, and we can stick them to the strikers and coins with double sided tape and what
fun, it can be a completely new game. Stronger magnets would be better. But still its a lot of fun you can see. Electrostatic Force. What was required here? We needed to charge an object, lets see if
the striker can be charged. No matter how much we tried, it was very difficult
to charge a normal striker. And we tried with different materials, and
then we saw that the striker we made with the PVC board was actually getting charged
and affecting the confetti. So if we hit the striker, it goes too fast
to attract the confetti. So we’ll just lift it above it. see its attracting it. So this way we’ve also shown electrostatic
force. Now how do we show gravity on the board….mmm? i was wondering but suddenly the owner of
the board came and took the board away. And as soon as it is lifted at an angle, everything
falls. “Hey thanks buddy, not only for the board
but you also just helped to show how the force of gravity effects all the coins on the board
and like it affects everything around us. Things required for the TIY project. Full set of carrom. Striker launcher. Sponge or foam. Plasticine or clay. Carrom Powder. Cycle with carrier. Rope. round magnets. Double sided tape or glue. Scissors. Drill machine with circle cutter. PVC Board or WPC. Confetti balls. So I hope you’ve enjoyed this new way of learning. i also hope you’ve subscribed to the channel
and move on to the next lesson. Our next lesson is on Pressure in solids and
liquids, and the fun will continue there.

3 thoughts on “FORCE and PRESSURE Part 1 – Physics Class 8th CBSE #1

Leave a Reply

Your email address will not be published. Required fields are marked *