What is Pressure? | Physics | Don't Memorise - Free Educational videos for Students in K-12

What is Pressure? | Physics | Don't Memorise - By Lumos Learning

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00:02	Mm . When you hammer and I nail , you
00:06	apply force on the flat side of the nail ,
00:09	the pointed side of the nail , which is in
00:10	contact with the wall , then applies the force on
00:13	the wall and tries to pierce it . Now ,
00:16	let me ask you an interesting question . What will
00:19	happen if you hammer the pointed side and try to
00:22	pierce the flat side of the nail ? You will
00:26	find it difficult to push the flat face of the
00:28	nail through the wall , even if you apply more
00:31	force than you did in the first case . What
00:34	is the reason for this ? The reason is that
00:37	the pressure applied by the tip of the nail on
00:39	the wall is more than the pressure applied by the
00:42	nails flat surface . But the question is why ?
00:46	First notice that the area of the tip of the
00:49	nail is very less as compared to the area of
00:52	its flat surface . This tells us that the area
00:56	of the surface on which the forces applied matters .
01:00	We will understand this in detail , but first let
01:03	us define pressure . We define pressure as the perpendicular
01:07	force , acting on the surface of an object per
01:10	unit area on which it's acting . It's easy force
01:14	acting for unit area . We already know that the
01:18	s R unit of force is Newton denoted by n
01:22	and that of the area is meter squared . So
01:25	the S I unit of pressure is Newton bomb meter
01:28	squared . It is also called Pascal which is denoted
01:32	by p A . Why is it called Pascal ?
01:37	It has given this name to honor the achievements of
01:39	a French scientist named Blaise Pascal for his contributions in
01:44	hydrostatic and hydrodynamics . Observe the equation carefully . Area
01:51	is in the denominator of the fraction . What is
01:54	this area ? Well , this area is nothing but
01:57	the area on which forces applied . Say I keep
02:01	the force constant and I keep increasing this area .
02:04	What will happen to the pressure ? Will the pressure
02:07	increase or decrease ? Use pure mathematical logic to answer
02:12	this . If I have a fraction and I keep
02:15	the term in the numerator constant and keep increasing the
02:19	term in the denominator , then will the fraction increase
02:22	or decrease ? Surely it will decrease so the pressure
02:28	will decrease if I increase the area while keeping the
02:31	force constant with this newfound knowledge , let's go back
02:35	to the example we saw earlier the nail and the
02:38	wall . Notice that we are also applying the force
02:41	perpendicular to the surface of the wall . The angle
02:45	between the nail and the wall is 90 degrees and
02:48	not anything else . If you notice the tip of
02:51	the nail has a very small area compared to the
02:54	flat surface of the nail , and hence the area
02:57	of contact with the wall reduces to great extent in
03:00	the first case . Hence , the pressure applied by
03:03	the tip on the wall is greater than the pressure
03:06	applied by the flat surface . That is why it
03:09	is easy for the tip of the nail to penetrate
03:12	through the wall . You can even use drill machines
03:16	to drill the hole into the wall . You see
03:19	that it has the pointed tip for the same reason
03:23	. You can easily cut the vegetables using the cutting
03:26	edge of the knife , but if you use the
03:29	blunt edge of the knife , it will be difficult
03:31	to penetrate it in . What is the reason in
03:34	this case ? Well , in the first sight ,
03:37	the two edges might look the same to us ,
03:40	but if you look at them carefully . The cutting
03:43	edge has small triangle like shapes which shop out of
03:46	points . The other edge has nothing of these ,
03:50	so if you cut a vegetable with the cutting edge
03:52	, the area of contact between the vegetable and the
03:55	knife is greatly reduced . Hence more pressure is applied
03:59	on the vegetables using cutting edge of the knife area
04:04	used to cut . The trees also have sharp cutting
04:07	edges instead of placid ones . It increases the pressure
04:10	on the tree due to the less area of contact
04:14	. The examples that we've seen so far are applications
04:17	of high pressure . It's about how high pressure is
04:21	useful to us in some cases . But it is
04:24	not always the case . There are situations where we
04:27	require low pressure . Let us see some applications or
04:31	advantages of low pressure . We use no shoes to
04:35	walk on snow . The reason for that is simple
04:39	. Due to the larger area in contact with the
04:42	snow . Snow shoes reduces the pressure on the snow
04:46	. We are able to walk on it without our
04:48	feet sinking deep inside . In case of normal shoes
04:52	due to comparatively smaller area of contact , the pressure
04:55	on snow is more and it sinks our feet deep
04:58	inside . Note that the force applied on the snow
05:01	in both the cases is the same . This force
05:05	is nothing but our weight on the snow . Have
05:08	you ever wondered why the wheels of an army tank
05:11	run on the steel tracks rather on the ground ,
05:14	notice that the wheels are on steel tracks and are
05:17	not touching the ground ? The Army tank is huge
05:20	in size . If the wheels run on ground due
05:24	to less contact area with the ground , the pressure
05:26	on the ground will be massive . However , the
05:29	tracks have much larger area of contact with the ground
05:32	, and hence the pressure on the ground is reduced
05:35	to a great extent . In all the examples that
05:38	we have seen in this video , it is the
05:41	solid , which is applying pressure on another solid to
05:45	liquids also apply pressure . We will see that in
05:48	the next video

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DESCRIPTION:

Do we know the real meaning of Pressure? When does Pressure increase or decrease? What is it dependent on? Watch this video to know more.

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