Syllabus learning topics will be discussed here. All children and parents are free to participate
Date: 08 Jul 2009 03:12
Number of posts: 12
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Students, under this head we shall study the concepts of Force and Pressure. Though the text book explains everything…and we shall study that in the classroom…here I will try and take you a little further. We will explore how force and pressure play an active role in our lives, how force and pressure are linked and how we can use them to our advantage in our daily lives. Also, I would encourage students to discuss with me their queries and clear out their confusions.
Pressure and Force are very closely linked with one another. Force acting per unit area is called Pressure. Its unit, like any other physical unit can be derived from its formula……Pressure = Force/Area
this gives…..Pressure = Newton/m2 (in SI system)
N/m2 is referred to Pascal (Pa)
Thus, 1 Pa = 1 N/m2
If a number of vertical forces are acting on a flat surface….they call all be summed up and together called Thrust. In such a situation:
Pressure = Force/Area = Thrust/Area
Simple sums or numericals can be based on the above relationships. these have been discussed in the text book on pages 140-141
Pressure is measured with the help of a very simple device called a MANOMETER. Refer below for a simple pictographic representation:
In fig 2-1 the liquid height in both columns is the same….indicating equal pressure from the air-side on both limbs of the tube. In fig 2-2 we can say that the pressure is more from the left side…and this causes the right side liquid to rise. In the 3rd figure….the pressure direction becomes vice versa.
In a manometer, Pressure differences are indicated by the difference in height of the liquid columns. The limb in which the liquid height is less is the one experiencing greater pressure…and vice-versa. The greater the Pressure difference between the 2 limbs, greater is the difference in liquid levels.
Some properties of Pressure may be summed up as follows:
- Pressure in a liquid is greater at greater depths
- At a particular depth, Pressure is the same in all directions
- Pressure increases with the increasing density of the liquid. In other words, at a particular depth the Pressure increases as density increases
- At a articular depth, Pressure is the same in all directions
All of above can be proved with the help of a manometer
Lets call it a day, today. We shall discuss some examples and Q&A in class. Pascals Law will follow in my next upload.
9 July 09: Pascals Law
A law of physics which states that a confined fluid (a liquid in a closed container) transmits externally applied pressure uniformly/equally in all directions. More exactly, in a stationary fluid, an external force is transmitted at the velocity of sound throughout the fluid. The force acts normal (at right angles) to any surface. This natural phenomenon is the basis of the balloon, hydraulic jack, and related devices.
The above fig shows equal pressure distribution in all directions when external force is applied
A Hydraulic Jack used to lift a car
Air Pressure or Atmospheric Pressure
Air pressure is the force exerted on you by the weight of tiny particles of air (air molecules). Although air molecules are invisible, they still have weight and take up space. Since there's a lot of "empty" space between air molecules, air can be compressed to fit in a smaller volume.
When it's compressed, air is said to be "under high pressure". Air at sea level is what we're used to, in fact, we're so used to it that we forget we're actually feeling air pressure all the time! This is also because the pressure inside our bodies is almost exactly equal to the outside atmospheric pressure at sea level…and the two balance out each other.
As we go up in altitude….like when we go up a mountain or take a plane ride….the air pressure keeps decreasing since the column of air above us within the atmosphere is decreasing. This causes breathing problems…and the inside pressure may exceed the outside one resulting in nose bleeding etc. Mountaineers wear oxygen masks while modern aircraft have pressurized air cabins.
Air pressure can tell us about what kind of weather to expect as well. If a high pressure system is on its way, often you can expect cooler temperatures and clear skies. If a low pressure system is coming, then look for warmer weather, storms and rain.
Weather forecasters measure air pressure with a barometer. Barometers are used to measure the current air pressure at a particular location in "inches of mercury" or in "millibars" (mb). A measurement of 29.92 inches of mercury is equivalent to 1013.25 millibars.
Some properties of Air Pressure (Also ref pgs143-145 for various activities. We shall also perform them in class next week. Each child should bring 1 glass, some water, a straw and a small piece of square cardboard that can cover the mouth of the glass)**
- Air exerts pressure
- Air pressure acts in all directions
- Air pressure decreases with increasing altitude
Some uses of Air Pressure
- using a straw
- a doctors syringe etc
Date…..20 July 09 - Friction:
Factors affecting Friction:
The concept of Limiting Friction:
Thanks for Working So Hard , to make our knowledge broader.
Sir I had to ask one Question :-
Sir , As we see that an Aircraft is Landing and it is applied Reverse Thrust , but it still goes moving in the Forward , So What will we call it ?
Waiting Eagerly For Your Reply
sir, i want to know :- what is an displacement?
Pankaj….displacement is the shortest distance between the starting and end points in a journey. So, if you run around a 400m track….your distance is 400m while displacement is 0 since your start and end points co-incide.
Also, displacement is a vector as compared to distance which is a scalar quantity.
Some basics on the concept of Force:
One of the foundation concepts of physics, a force may be thought of as any influence which tends to change the motion of an object. The action of forces in causing motion is described by Newton's Laws under ordinary conditions, although there are notable exceptions.
Our present understanding is that there are four fundamental forces in the universe:
- the gravity force,
- the nuclear weak force,
- the electromagnetic force, and
- the nuclear strong force
As we go along we will have more uploads and assignments here on Force. Meanwhile, I want all students of both Class IX sections at MBIIS to complete the unsolved questions from the Chapter on Motion from H.C.Verma and submit me by Fri 24 July 09.
Feel free to discuss your problems here on this forum after logging in.
I am not able to understand the concepts you taught me, in class on wednesday. So, I want you to post them as soon as possible, else you will head with other topics.