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dancing raisins

For this experiment you will need:

• a can of colorless soda (e.g., 7-Up or Sprite)
• a tall, clear glass or plastic cup
• several raisins (fresh raisins work the best)

Pour the can of soda into the tall glass. Notice the bubbles coming up from the bottom of the glass. The bubbles are carbon dioxide gas released from the liquid.

Drop 6 or 7 raisins into the glass. Watch the raisins for a few seconds. Describe what is happening to the raisins. Do they sink or float? Keep watching; what happens in the next several minutes?

Raisins are denser than the liquid in the soda, so initially they sink to the bottom of the glass. The carbonated soft drink releases carbon dioxide bubbles. When these bubbles stick to the rough surface of a raisin, the raisin is lifted because of the increase in buoyancy. When the raisin reaches the surface, the bubbles pop, and the carbon dioxide gas escapes into the air. This causes the raisin to lose buoyancy and sink. This rising and sinking of the raisins continues until most of the carbon dioxide has escaped, and the soda goes flat. Furthermore, with time the raisin gets soggy and becomes too heavy to rise to the surface.

You might want to try other objects to see if they exhibit this behavior. Any object whose density is just slightly greater than water’s and has a rough surface to which the gas bubbles can attach should be able to dance in the carbonated water. Some of the more common dancing substances are mothballs and pieces of uncooked pasta. Try putting other objects in the carbonated water. Can you find other substances that dance?

Carbonated beverages are prepared by putting the beverage into a can under high pressure of carbon dioxide gas. This high pressure causes the carbon dioxide gas to dissolve in the liquid. When you open a can of soda, the noise you hear is produced by the carbon dioxide gas as it rushes out of the can. When the can is opened, the decreased pressure allows some of the carbon dioxide gas dissolved in the liquid to escape. This is what makes the bubbles in a soft drink.

Another way to do this experiment is to generate the carbon dioxide gas using the reaction of baking soda and vinegar. Fill your glass about 1/2 full with water. Add one teaspoon of baking soda and stir until it is dissolved in the water. Add 6 or 7 raisins to the glass. SLOWLY pour in vinegar until the glass is about 3/4 full. The vinegar and baking soda react to form carbon dioxide bubbles, and the raisins will dance just as in the soft drink! 

floating eggs

Materials you will need: • Table Salt • Two Bowls • A Tablespoon • Warm Tap Water • Two Eggs • A Friend

Steps:

1. Fill both bowls with warm tap water.
2. Add a few tablespoons of salt to one of the bowls of water and stir it really well, until the salt has dissolved in the water.
3. Carefully place a egg in each bowl.
4. One egg will float and the other will sink. 

Which egg floats?  _____________.   Do you know why?

The salt water is heavier than the plain tap water, so the weight of the egg does not have to push away as much water to make space for itself and therefore it floats.  

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Oil Well

Numericals assignment- class IX

Q What is the momentum of a man of mass 75kg when he walks with a uniform velocity of 2m/s?

Q What is change in momentum of a car weighing 1500 kg when its speed increases from 36km/h to 72km/h uniformly?

Q A man throws a ball weighing 500g vertically upwards witha speed of 10m/s.

1) what will be its initial momentum?

2) What would be its momentum at the highest point of his flight?

Q A truck starts from rest and rools down a hill with constant acceleration. It travels a distance of 400m in 20s. Find the force acting on it if its mass is 7 metric tonnes. ( 1 metric ton= 1000kg)

Q A car of mass 2400kg moving with a velocity of 20m/s is stopped in 10s on applying brakes. Calculate the retardation and the retarding force.

Q For how long should a force of 100N act on a body of 20kg so that it acquires a velocity of 100m/s?

Q A body of mass 2kg is at rest. What should be the magnitude of force which will make the body move with a speed of 30m/s at the end of 1s?

Q An unloaded truck weighing 2000kg has a maximum acceleration of 0.5 m/s*s. What is the maximum acceleration when it is carrying a load of 2000kg?

Q The car A of mass 1500kg, travelling at 25m/scollides with another car B of mass 1000kg travelling at 15m/s in the same direction. After collision the velocity of car A becomes 20m/s. Calculate the velocity of car B after collision.

Q A bullet of mass 10g moving with a velocity of 400m/s gets embedded in a freely suspended wooden block of mass 900g. What is the velocity acquired by the block?

Q A 10g bullet travelling at 200m/s strikes and remains embedded in a 2kg target which is originally at rest but free to move. At what speed does the target move off?

Q A gun of mass 3kg fires a bullet of mass 30g. The bullet takes 0.003s to move through the barrel of the gun and acquires a velocity of 100m/s. calculate:

a) the velocity with which the gun recoils.

b) the force exerted on gunman due to recoil of the gun.

Q A ball X of mass 1kg trvelling at 2m/s has a head on collision with an identical ballY at rest. X stops and Y moves off. Calculate the velocity of Y after the collision.

Q A boy of mass 50kg running at 5m/s jumps onto a 20kg trolley travelling in the same directionat 1.5m/s. What is their common velocity?

Q A girl of mass 50kg jumps out of a rowing boat of mass 300kg on to the bank, with ahorizontal velocity of 3m/s. With what velocity does the boat begin to move backwards?

Q The velocity of a body of mass 10kg increases from 4m/s to 8m/s when a force acts on it for 2s.

a) What is the momentum before the force acts?

b) What is the momentum after the force acts?

c) What is the gain in momentum per second?

d) What is the value of the force?

Q Calculate the value of acceleration due to gravity on the surface of the moon?

Q The earth's gravitational force causes an acceleration of 5m/s*s in a 1kg mass somewhere in space. How much will the acceleration of a 3kg mass be at the same place?

Q To estimate the height of a bridge over a river, a stone is dropped freely in river from bridge. The stone takes 2s to touch the water surface. Calculate the height of bridge from the water level.

Q A cricket ball is dropped from a height of 20m

a) Calculate the speed of the ball when it hits the ground.

b) Calculate the time it takes to fall through this height.

Q A body has a weight of 10kg on the surface of the earth. What will be its weight when taken to the centre of the earth?

Q A stone resting on the ground has a gravitational force of 20N acting on it. What is the weight of the stone

Gravitation- Class IX

Q According to Universal law of gravitation- every body on the earth attracts every other body with a gravitational force, why then this force does not cause any motion in the objects?
Ans Though the various objects on this earth constantly attract each other, they do not cause any motion because-
1) Each body experiences multiple forces from different directions and most of these forces get cancelled from each other.
2) The gravitational force of attraction between them is very small due to their comparatively small masses.

Gravitation and Newton's laws of motion

According to Third law of motion every action has equal and opposite reaction. This means that if earth attracts a body towards it witha force,F then the body also attracts earth with same force but in opposite direction i.e. -F. But we know that earth does not move towards the object because according to second law of motion, F=ma

a=F/m

As we see that acceleration is inversely proportional to m, therefore a negligible acceleration is produced in earth due to its high mass.

Acceleration due to gravity

If we drop a body of mass 'm' from a distance 'R' from centre of earth of mass 'M', then earth will exert a force of gravitation on the body,F

F=G M m/R*R - 1

According to second law of motion, F=ma -2

Equating 1 and 2

GMm/R*R = ma

a= GM/R*R

Since we know that in case of free fall, a= g (acceleration due to gravity),

g= GM/R*R

Putting values, we get g=9.8 m/s*s

Dependence of acceleration due to gravity

1) Since acceleration due to gravity is independent of mass of object i.e. 'm', therefore, both light and heavy objects are accelerated by same amount.

2) As 'g' depends on 'R', the value of 'g' varies at poles and equator. Since, 'R' is more at equator, 'g' is small at equator and 'R' is less at poles, therefore, 'g' is more at poles.

Weight on moon

Let We= weight on earth and Wm= weight on moon

Wm= GM*m/R*R where M is mass of moon, m is mass of object and R is radius of moon

Now, mass of earth is 100 times mass of moon and radius of earth is 4 times radius of moon

We= G 100M*m/4R*4R

We= 100GmM/16R*R

Wm/We= 16/100

or approximately, Wm/We=1/6

Therefore, weight of an object on moon is 1/6th of weight of that object on earth.

Difference between mass and weight
Mass
1) The mass of an object is the quantity of matter contained in it.
2) The S.I. unit of mass is kilogram (kg).
3) The mass of an object is constant.
4) The mass of an object can never be zero.

Weight
1) The weight of an object is the force with which it is attracted towards the centre of the earth.
2) The S.I. unit of weight is Newton (N).
3) The weight of an object is not constant. It changes with the change in acceleration due to gravity (g).
4) The weight of an object can be zero. e.g. in the interplanetary space, where g=0, the weight of an object becomes zero.

Equations of motions for freely falling bodies

1) v=u+gt

2) h=ut+ 1/2gt*t

3) v*v= u*u+ 2gh

IMPORTANT POINTS TO REMEMBER

1) The physical quantities having vertically upward motion are assigned +ve values whereas the physical quantities having downward motion are assigned -ve values.

2) The acceleration due to gravity of earth is always taken -ve.

3) When a body is dropped freely from a height, its initial velocity 'u' is zero.

4) When a body is thrown vertically upwards, its final velocity 'v' becomes zero.

5) The time taken by a body to rise to the highest point is equal to the time it takes to fall from the same height.

Class ix

Chapter- Force and Laws of Motion
APPLICATIONS OF LAWS OF MOTION

Class-IX

First law of motion

Introduction: First law of motion states that- ‘A body at rest will remain at rest and a body in uniform motion will continue in uniform motion with same velocity unless it is compelled by an external force to change its state of rest or of uniform motion.’ The property of a body due to which it resists a change in its state of rest or of uniform motion is called Inertia. So, we can say that first law defines inertia.
Physical significance of inertia: Mass is the measure of inertia of a body. Heavier objects have more inertia than lighter objects.
Practical applications/ Related phenomenon: 1) When a hanging carpet is beaten with a stick, dust particles start coming out of it. This is because the force of stick makes the carpet move to and fro slightly but dust particles tend to remain at rest due to their inertia and hence seperate from the carpet.

2) When a tree (having flexible stem) is shaken vigorously, its fruits and leaves fall down. This is due to the fact that when branch of tree is shaken, it starts moving to and fro but the fruits and leaves attached to it tend to remain at rest due to inertia and hence detach from tree and fall down.
3) When a car or bus stops suddenly, passengers are jerked forward because due to force of brakes bus stops but passengers tend to remain in uniform motion. The seat belts are provided in cars so that if a fast running car stops suddenly due to some emergency, then the passengers are not thrown forward violently, and injury is prevented.
4) When a car or bus starts suddenly, passengers are thrown backward because the vehicle starts but passengers tend to remain at rest.
5) When a car or bus turns a corner sharply, we tend to fall sideways because of our inertia or tendency to continue moving in a straight line.
6) It is dangerous to jump out of a moving bus because the jumping person, who was moving with high speed of the bus, would tend to remain in motion due to inertia even on falling to the ground and get hurt due to resistance offered by ground.
Definition of FORCE: Force is something which changes or tends to change the state of rest or of uniform motion of a body.

Second Law of Motion

Introduction: Second law of motion states that-‘The rate of change of momentum of a body is directly proportional to the applied force, and takes place in the direction in which the force acts.’
Force α Change in momentum / time taken
Formula: F=ma where, m=mass of body, a= acceleration produced on applying force F
NOTE: first law is special case of second law (explained in class)
Practical applications/ Related phenomenon: 1) A cricket player moves his hands backward on catching a fast cricket ball. This is because a fast moving cricket ball has a large momentum. In stooping such a ball its momentum has to be reduced to zero. Now, when a cricket player moves his hands back, the time taken to reduce momentum of ball to zero is increased which reduces the rate of change of momentum( rate of change of momentum α change in momentum/ time taken; if denominator is increased, whole value decreases, so force decreases). Hence, a small force is exerted on the hands of player and he does not get hurt.
2) During athletics meet, a high jumping athlete is provided either a cushion or a heap of sand on the ground to fall upon. When the high jumper falls on a soft landing site, then the jumper takes a longer time to come to a stop. Thus rate of change of momentum is less due to which small stopping force acts on athlete’s body and the athlete does not get hurt.

Third Law of Motion

Introduction: Whenever one body exerts a force on another body, the second body exerts equal and opposite force on the first body i.e. to every action there is an equal and opposite reaction.
NOTE: Both the forces are opposite, so if one is positive, other will be negative.
Physical significance: Forces always exists in pairs.
Practical applications/ Related phenomenon: 1) When we walk on the ground, then our foot pushes the ground backward and in return ground pushes our foot forward. The forward reaction exerted by the ground on our foot makes us walk forward.
2) When a bullet is fired from a gun, the force sending the bullet forward is equal to the force sending the gun backward. But due to the high mass of the gun, it moves only a little distance backward and gives a backward jerk or kick to the shoulder of the gunman. The gun is said to have recoiled.
3) In jet airplanes and rockets, the hot gases obtained by rapid burning of fuel rush out of a jet (nozzle) at the rear (back) end of aircraft at a great speed. The equal and opposite reaction of the backward going gases pushes the aircraft forward at a great speed.
4) Moving of a boat is also similar to those of aircrafts with the difference that backward force is provided by oars (chapu).
5) When a man jumps out of a boat to the bank of the river, the boat moves backwards, away from him. This is because while stepping out of the boat, man pushes the boat in backward direction with his leg (action). In return of this boat exerts an equal force on man in forward direction which makes the man move forward.
6) When firemen are directing a powerful stream of water on fire from a hose pipe, they have to hold the hose pipe strongly due to its tendency to go backward. The backward movement of hose pipe is due to the backward reaction of water rushing through it in the forward direction at a great speed.
7) To make the cart move, the horse bends forward and pushes the ground with its feet. In return to this ground exerts a forward push on horse. When the forward reaction to the backward push of the horse is greater than the opposing frictional forces of the wheels, the cart moves.

Law of Conservation of momentum

Introduction: The law of conservation of momentum states that ‘When two or more bodies act upon one another, their total momentum remains constant provided no external forces are acting.’
Total momentum before collision= total momentum after collision
Practical application/ Related phenomenon: The chemicals inside the rocket burn and produce high velocity blast of hot gases. These gases pass out through the tail nozzle of the rocket in the downward direction with tremendous seed or velocity, and the rocket moves up to balance the momentum of the gases. Although the mass of gases emitted is comparatively small, but they have a very high velocity and hence a very large momentum. An equal momentum is imparted to the rocket in the opposite direction, so that, inspite of its large mass, the rocket goes up with a high velocity.



Q Why more force is required to move a heavier body?
A A greater force is required to move a body with more mass. This can be explained as follows-
a) First law of motion- According to first law of motion, a body with more mass has more inertia and more the inertia of a body, more is its tendency to resist change in its state of rest. So, a greater force is required to overcome this high inertia.
b) Second law of motion- According to second law of motion, F=ma i.e. Fα m when ‘a’ is constant. So, greater the mass of a body, more force it requires to produce a particular amount of acceleration.

Q How does a rocket move?
A A rocket moves due to gases produced from its nozzle. This can be explained as-
a) Third law of motion- see explanation above
b) Law of conservation of momentum- see explanation above

Q Why are seat belts used in cars?
A Seat belts are used in cars to save the passengers from injuries. This is because

a) First law of motion- see explanation above
b) Second law of motion- In a fast moving car when brakes are applied, car stops suddenly. Due to this car’s large momentum is reduced to zero in a very short time. The stretchable seat belts worn by the passengers of the car increase the time taken by the passengers to fall forward. Due to longer time, the rate of change of momentum of passengers decreases and hence less stopping force is applied on passengers. This prevents the passengers from getting hurt seriously.

NOTE: Similarly, there are many other phenomena which cannot be explained simply by one law of motion.

Class 10- assignment

CLASS 10

Topic- Magnetic effects of current

Q1 What are the factors on which the strength of magnetic field produced by a current carrying solenoid depends?
Q2 State the advantages of electromagnet over a bar magnet.
Q3 What is the importance of magnetism in the medical field?
Q4 Define- 1) Magnetic field 2) Magnetic lines of force
Q5 How can you prove that electricity produces magnetic effect?
Q6 Explain-1) Fleming's left hand rule 2) Right hand thumb rule
Q7 State an activity to prove that a current carrying conductor when placed in a magnetic field experiences a force.
Q8 What are the similarities between a bar magnet and a current carrying solenoid?
Q9 What are the differences in the construction of a simple motor and a commercial motor?
Q10 What is a commutator? Explain in context of an electric motor.
Q11 What is a magnetic compass needle? How is it useful?
Q12 What effect is produced when current is passed through a circular loop?
Q13 What is a Galvanometer?

Q14 What is electromagnetic induction? How is it related with Fleming's right hand rule?

Q15 What is overloading? When does it occur?

Q16 How many wires are present in a plug? What are their uses?

Q17 Define- 1) Alternating current 2) Direct current

Q18 Explain the construction and working of a DC generator.

INSTRUCTIONS:

1) Submit your copies on Tuesday with Q1-12 of assignment, all inbox questions of NCERT and Q8-12 of back exercise.

2) I'll discuss the problems on Monday.

Writing with a feather

Purpose:

For students to learn about the writing tools used by colonists who utilized the local plant materials, before the invention of pencils and pens.

Materials:

Large feathers (peacock or pheasant feathers are the best)
Scissors or pen knife
10 walnut shells
1 cup water
1/2 teaspoon vinegar
1/2 teaspoon salt
Hammer
Old cloth/rag
Saucepan
Small jar with lid
Strainer

Lab Procedure:

1. Using hammer, crush the shells in the cloth

2. Add the shells and water to the saucepan. Bring to a boil, simmer 45 minutes or until dark brown. (Much of the water will evaporate.)

3. Remove the ink from the burner and let it cool.

4. Strain it into the jar and add vinegar and salt (this preserves the ink).

5. Use scissors or pen knife to cut the end of the feather so it's on an angle (/).

6. Write away!

assignment -6

The World of Living

1) Give 1 example for each of the following:
a) unicellular organism-
b) a herb-
c) flowering plant-

2) Give one word for the following-
a) basic unit of life-
b) plants which survive for only 1 year-
c) removal of waste products from the body-
d) plants which have height of 3 feet to 7 feet-

3) Answer the following-
a) How are animals classified on the basis of reproduction?
b) Draw the structure of Amoeba.
c)Define- 1) Response 2) Stimuli
d) How are plants useful to us?