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Lesson Posted on 19 Mar Learn ICSE Schools
Give Reasons - Force & Pressure - Class 8 - ICSE
Tanusri Sengupta
I have provided tuition for the past 20 years to ICSE, CBSE, and other students. I am a corporate coach...
Answer:
Birds that walk on leaves floating on the surface of the water have wide feet. This is because wide feet increase the area of contact with the leaves. So, they exert less pressure on the leaves, allowing them to walk on these leaves.
Answer:
When the nozzle of a syringe Is dipped in a liquid and its piston is withdrawn, a region of low pressure is created in the syringe. The atmospheric pressure acting on the surface of the liquid is greater and hence forces the liquid to rise in the syringe.
Answer:
Pillars of a bridge have a broader base than the top. This is done to reduce the pressure exerted on the ground by the enormous weight of the bridge. As pressure is inversely proportional to the area of contact, so if the base is broader, the area of the contact increases, reducing the pressure on the ground due to the weight of the bridge.
Answer:
Pressure is greater at 10 m below the surface of the sea as compared to that at 5 m below the surface of the sea. This is because pressure exerted by a liquid increases with depth.
Answer:
Water is not used as a barometric fluid as it has less density due to which it will have to rise to a height of 10.5 m to balance the atmospheric pressure. Moreover, it vaporizes in vacuum and thus, never records the true atmospheric pressure.
Answer:
Although both women’s heights are the same, they also carry the same weight when they walk. But the woman wearing the sandal with flat heels will be more comfortable than the woman wearing sandals with pointed heels while walking on a sandy beach. This is because the flat soles have a larger surface area as compared to sandals with pointed heels. Also, the pressure exerted by the woman with pointed heels will be greater as compared to that of the woman wearing sandals with flat soles. This increased pressure will make walking on sand in sandals with pointed soles difficult.
Answer:
Safety pins and drawing pins have narrow and sharp tips because the smaller surface area of the tip causes a high pressure and, therefore, makes it easier for these objects to pierce through a given material.
Answer:
The hand flour grinder is provided with a handle near its rim to increase the moment arm so that even a small force applied can produce a large turning effect.
Answer:
Force, area and pressure are related by the following expression.
If the force applied is doubled for the same area, then the pressure will also double.
Answer:
A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the ‘flat’ shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.
Answer:
The pressure of air inside our body is the same as that of the atmosphere. Therefore, we do not experience its effect.
Answer:
Since the pressure of liquid increases with the increasing depth of sea. Specially designed suits protect scuba divers from the huge pressure of the water underneath.
Answer:
The initial force is muscular force which sets the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.
Answer:
Rod A will go deeper as it has a smaller area of contact, therefore the same force produces more pressure. In case of rod B the same force produces less pressure.
Answer:
Blunt blades have a larger area compared to the sharp-edged blades. Thus, the applied force produces a lower pressure in case of blunt blades, which makes it difficult to cut the cloth.
Volume of water in each vessel is shown above. Arrange them in order of decreasing pressure at the base of each vessel. Explain the reason.
Answer:
Pressure of a liquid column depends upon the height of the liquid column and not on volume of the liquid. Decreasing order of pressure at the base of each vessel is B > D > A > C.
How do balloons stick to walls?
How Shreya bent the water stream by bringing a big balloon near it and without touching it?
What values of Shreya are shown here?
Answer:
On rubbing the balloon with hair or clothes, it acquires negative charges. The negative charges are attracted to the positive charges on the wall and balloon sticks to the wall.
Negative charge on the balloon attracts positive charge on water molecules. Thus, bent the water molecules.
Shreya is dutiful, friendly with scientific aptitude.
Answer: The snow shoes have large, flat soles so they exert less on the soft snow and stop the wearer from sinking into it.
Answer: When we sit on the seat of a bicycle, the force exerted by the body weight compresses the spring and changes its shape.
Answer: Air exerts pressure on the inner walls of the balloon causing it to expand and get inflated.
Answer: The wide belts increase the area and reduce the pressure. This avoids sinking of the tank into the ground.
Answer: The high pressure produced by the gas or water molecules on the walls of the balloon causes it to expand and get inflated.
Answer: This is so because water pressure is less in the upstairs tap due to lesser depth.
Answer: We do not get crushed because the atmospheric pressure acting on our body from outside is balanced by the blood pressure acting from inside.
Ans. Lesser the area, larger the pressure for the same force applied. Therefore, it is easier to cut with sharp knives than blunt ones, with same force.
Answer: The cutting edges of tools like blades, knives etc., are provided with sharp edges to cut the things easily because the smaller the area, larger the pressure on a surface for the same force.
Answer: The tip of the sewing needle is sharp so that due to its sharp tip, the needle may put the force on a very small area of the cloth, producing a large pressure sufficient to pierce the cloth being stitched.
Answer: By this they increase the area of contact of the load with their head. So, the pressure on their head is reduced and they find it easier to carry the load.
Answer: Shoulder bags are provided with broad straps and not thin strap so that the weight of the bag may fall over a large area of the shoulder of the child producing less pressure on the shoulder.
Answer: The two forces acting on the rocket are the force of gravity, which pulls the rocket towards the ground, and the force of friction due to earth’s atmosphere, which opposes its motion.
Answer: Many times we see a fountain of water rushing out of the leaking joints (or holes) in the pipes of main water supply line. It is due to the very high pressure exerted by water on the sides (or walls) of the pipes that such a fountain of water is formed.
Answer: When the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the pressure inside the syringe is lowered. The greater atmospheric pressure acting on the surface of the liquid pushes the liquid up into the syringe.
Answer: At high altitudes, the atmospheric pressure becomes much less than our blood pressure. Since, our blood is at higher pressure than outside pressure, therefore, some of the blood vessels in our body burst and nose bleeding takes place at high altitudes.
Answer: In this case, muscular force is acting in upward direction and the force of gravity is acting in downward direction. The two forces are equal in magnitude but opposite in direction. Therefore, the net force on the bucket is zero. Hence, there is no change in its state of motion.
Answer: The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. Since most of the atmosphere’s molecules are held close to the earth’s surface by the force of gravity, air pressure decreases as we go higher up above the earth’s surface.
Answer: When a plastic comb is rubbed in dry hair, the comb gets electric charges by friction. And when this electrically charged comb is brought near tiny pieces of paper, it exerts an electrostatic force of attraction on them. Due to this electrostatic force, the tiny pieces of paper move towards the comb and stick to it.
Answer: The weight of air in a column of the height of the atmosphere and area 10 cm × 10 cm is as large as 1000 kg. The reason we are not crushed under this weight is that the pressure inside our bodies is also equal to the atmospheric pressure and cancels the pressure from outside.
Answer: This is due to the fact that since there is no air inside, the unopposed atmospheric pressure acting over the whole surface of the hemispheres from outside presses them very, very hard and does not allow them to be separated.
Answer: When a man stands on a cushion then only his two feet are in contact with the cushion. Due to this, the weight of man falls on a small area of cushion producing a large pressure. This large pressure causes a big depression in the cushion. On the other hand, when the same man is lying on the cushion, then his whole body is in contact with the cushion. In this case, the weight of man falls on a much larger area of the cushion producing much smaller pressure. And this smaller pressure produces a very little depression in the cushion.
Lesson Posted on 23 Feb Learn Mathematics
Why do most of the students face difficulty in maths ?
Rakesh Shanbhag
I'm an IT professional with over 5 years of teaching experience for students for all thr boards (CBSE,...
In my opinion, most of the students would have done great in maths in childhood (say 1st to 4th STD), not because they were studying well, it might be because the concepts were easy.
But what happens after that is slight shift in focus. It's not that they are bad now. It's just that now they start feeling the effect of weak basics.
It all starts with LCM, HCF, Decimals and goes on to find x and y, solving equations.
People who are good with this, can actually focus more on only concepts from here on, whereas the weak student has to focus on both concepts as well as the process to solve.
This gap in understanding continues and student with good basics scores good marks only studying 30minutes a day and a student with weak basics struggles to score average marks even after spending 2-3 hours.
This makes most of the students say, 'I hate Mathematics'
read lessLesson Posted on 27/07/2023 Learn CBSE Schools
Anamika
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Lesson Posted on 24/07/2023 Learn CBSE Schools
Heredity in plants and animals
Deleted
HEREDITY
Important concepts of Heredity:
There are different terms in this chapter that need to be understood well to get what exactly heredity is!
Genotypic ratio=> 1:2:1
LAWS OF HEREDITY:
SIGNIFICANCE OF DNA;
GENES: It carries genetic information to help in the making of protein.
VARIATION: Difference in characteristics or genetic information from parents to offsprings.
BIOTECHNOLOGY: The application of technological procedures on organisms used to bring out the best from the existing creatures and modifying the lacking capacity.
RNA FINGERPRINTING Technology: It is the technology used for comparing the different DNA segments and analysing the result under gel electrophoresis.
GENETIC ENGINEERING: This is the technique used with the modern technology to bring out the desired change in the genome.
For example: To get the desired growth in plant species genetic engineering helps.
CLONING: Developing the clones in the laboratory that have similarities with the template. It is nothing but producing a copy of an original.
Willmut was successful scientist whonwho first cloned a sheep.
LIMITATIONS OF BIOTECHNOLOGY:
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Lesson Posted on 04/07/2022 Learn State Board Schools
Mangesh Jaybhay
I am a tutor. I did my graduation Bachelor of Science(B.Sc) in statistics field from Savitribai Phule...
*Fraction addition :
When denominator is not same
Question:
Solve: [(2/5)+(3/7)]
Ans:
Using the rule
[(a/b)+(c/d)]
[(a×d)+(b×c)]/(b×d)
(ad+bc)/bd
By using this formula
We can solve
[(2/5)+(3/7)]
[(2×7)+(3×5)]/(5×7)
(14+15)/35
[(2/5)+(3/7)] = (29/35)
This is final answer.
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Answered on 10/11/2021 Learn Tuition Fee
Pranjal Mishra
Mathematics Teacher, Experience of 5+years M.Sc in Mathematics from University of Delhi
Hi Mahima I wouldn't disclose my locality but I also live here and according to my experience it's upto the background of the family as well as their the requirements from you.
If you are a beginner then start from 200/hr to 300/hr it would be easy for you to convert the parents.
You can also manipulate the fee but not less than +/- 50₹/hr.
Best wishes.
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Lesson Posted on 29/10/2021 Learn Montessori Schools
Nirmala Ravikumar
Hello 🙏 Nirmala tutor welcome you to view my profile Overall I will create a loving atmosphere...
Lesson Posted on 17/05/2021 Learn .Net Advanced
CBSE Class12 math's chapter 3 matrices example 4 & 5
Shoba
I worked as an assistant professor in engineering college, so I had experience in various area Like Handled...
Lesson Posted on 22/04/2021 Learn Physics
How to Solve Numericals in Physics?
Vaidnyanic
Vaidnyanic is my humble attempt to make studies interesting to students and make them more curious and...
Are you scared of numerical? Do you think you don't understand them? If yes, then read ahead.
See, it might be any exam, but numerical won't leave your back.
So let's talk about common problems and their solutions:
Problem 1: Sir, I am not able to understand what the numerical is saying!
Solution: It's simple, read again, find the meaning of the word and see again and again for words you don't understand. It's a problem of vocabulary or non-understanding of concepts.
Let me give you an example:
Force is mass multiplied by acceleration. So if I want to ask you to find the force and frame it like "Find force when mass is 5kg, and acceleration is 8 m/s²", I don't think anybody would have a problem. Now the same question when I frame it like " Find the rate at which momentum changes for a 5kg body moving with a constant rate of 8 m/s²" is the same question why did you feel it to be difficult? Firstly, because you might not know that the rate of momentum is a force as per Newtons 2nd law, nowhere does it mention mass or acceleration, and you might not know its units. So we can't get hold of a numerical either if we don't understand the words that the paper setter is using or simply are not aware of the concept.
I'll tell you a fun fact. Many times teachers interpret questions differently. So it is okay, and eventually, you will get the hang of it.
Problem 2: I make a lot of silly mistakes.
Solution: Practice! Practice! Practice! And work on your focus because we have Netflix, amazon prime, IPL, Anime and many more things in our life to distract us. BTW I have learned how to balance, so if I can, you can too! Find your distractions work on them learn to focus.
Know what everyone does is eventually stop doing numerical, and they avoid practice which is quitting. Don't do that. Tell yourself you can do it, and humans make errors. Be happy the next time you make a mistake and make sure you work on it and never repeat it.
How to approach numerical?
1) Find the concept hidden like in the above example; the concept is of force.
2) Identify the formula or formulas related to the concept. (While practising, it is okay if you look at the formulas rather than memorizing). In the example, the formula is F =M x A.
3) Try to fit the given data in the formula and see how you can get the asked data. So in the above example, since M and A are given, it's a matter of just putting the values. But what if instead of A, they give you U, V and S. As I can see, these are variables from the kinematic equations, and if A is constant, I can use them and find A and hence F.
4) Remember Units. I can't emphasize enough on this enough. Sometimes units will give you a helping hand.
PRACTICE! PRACTICE! PRACTICE!
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Lesson Posted on 17/03/2021 Learn ICSE Schools
Suvam Banerjee
I am a B.Tech Graduate from the West Bengal University of Technology giving home tuition. I have more...
Expected Utility: Theorems
The theory of expected utility was developed by the founders of game theory, namely John von Neumann and Oskar Morgenstern, in their 1944 book Theory of Games and Economic Behavior.
In a rather unconventional way, we shall first (in this section) state the main result of the theory (which we split into two theorems) and then (in the following section) explain the assumptions (or axioms) behind that result. The reader who is not interested in understanding the conceptual foundations of expected utility theory, but wants to understand what the theory says and how it can be used, can study this section and skip the next. Let O be a set of basic outcomes. Note that a basic outcome need not be a sum of money: it could be the state of an individual’s health, or whether the individual under consideration receives an award, or whether it will rain on the day of her planned outdoor party, etc. Let L (O) be the set of simple lotteries (or probability distributions) over O. We will assume throughout that O is a finite set: O = {o1,o2,..., om} (m ≥ 1). Thus, an element of L (O) is of the form o1 o2 ... om p1 p2 ... pm with 0 ≤ pi ≤ 1, for all i = 1,2,...,m, and p1 + p2 +...+ pm = 1. We will use the symbol L (with or without subscript) to denote an element of L (O), that is, a simple lottery. Lotteries are used to represent situations of uncertainty.
For example, if m = 4 and the individual faces the lottery L = o1 o2 o3 o4 2 5 0 1 5 2 5 , then she knows that, eventually, the outcome will be one and only one of o1,o2,o3,o4, but does not know which one; furthermore, she can quantify her uncertainty by assigning probabilities to these outcomes. We interpret these probabilities either as objectively obtained from relevant (past) data or as subjective estimates by the individual.
For example, an individual who is considering whether or not to insure her bicycle against theft for the following 12 months knows that there are two relevant basic outcomes: either the bicycle will be stolen, or it will not be stolen. Furthermore, she can look up data on past bicycle thefts in her area and use the proportion of stolen bicycles as an “objective” estimate of the probability that her bicycle will be stolen.
Alternatively, she can use a more subjective estimate: she might use a lower probability of theft than suggested by the data because she knows herself to be very conscientious and – unlike other people – always to lock her bicycle when left unattended.
The assignment of zero probability to a particular basic outcome is taken to be an expression of belief, not impossibility: the individual is confident that the outcome will not arise, but she cannot rule out that outcome on logical grounds or by appealing to the laws of nature.
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