SAFETY FIRST

PISA QUESTIONS NCF 8/8/2020class VII-VIII

PISA Questions FORCE AND PRESSURE Class VIII Chapter 11

Select the most suitable alternative of the following MCQs.
Q.1 Force is a kind of –
(a) Push
(b) Pull
(c) Push as well as pull
(d) Non of these
Q.2 When the force is applied on an object, it can change- 
(a) Shape
(b) State of motion
(c) Direction
(d) All of these
Q.3 What is the S.I. Unit of force? 
(a) Dyne
(b) Newton
(c) Pascal
(d) Joule
Q.4 Which of following is a contact force? 
(a) Muscular force
(b) Gravitational force
(c) Electrostatic force
(d) Magnetic force
Q.5 When a magnet is brought near a magnetic compass, its needle shows deflection due to- 
(a) Gravitational force
(b) Frictional force
(c) Electrostatic force
(d) Magnetic force
Q.6 A plastic scale is rubbed with a woolen cloth. When it is immediately brought near bits of paper, the bits of paper are attracted towards it. This is due to- 

(a) Electrostatic force
(b) Magnetic force
(c) Gravitational force
(d) Frictional force
Q.7 The force acting on a unit area of a surface is called as- 
(a) Pressure
(b) Force
(c) Friction
(d) Gravity
Q.8 The S.I. Unit of pressure is-
(a) Dyne
(b) Pascal
(c) Newton
(d) Watt
Q.9 Which of the following exert the pressure?
(a) Solids
(b) Liquids
(c) Gases
(d)All of the above
Q.10 The pressure of liquid increases with 
(a) Increasing the volume of container
(b) Increasing height of liquid
(c) Increasing the base of water container
(d) Any one of the above
Q.11 Atmospheric pressure will be minimum at -
(a) Sea level
(b) Very high altitude like 8000 feet
(c) Above 1000 feet
(d) All of these
Q.12 Atmospheric pressure will be maximum at- 
(a) above 5000 feet
(b) above 3000 feet
(c) above 2000 feet
(d) Sea level
Q.13 Look at the three bricks in three different positions kept on a table. In which brick number the pressure will be maximum? 

(a) 1
(b) 2
(c) 3
(d)Equal in all the three positions
Q.14 At the four points A, B, C and D there are taps in this water container. Which tap will have least pressure?

(a) A
(b) B
(c) C
(d) D
Q.15 In question number 14, which two points the pressure of water will be equal? 
(a) A & B
(b) A & C
(c) B & C
(d) B & D
Q.16 Two boys are applying forces from opposite side on a box. If box moves in left direction, which of the following statement is correct?

(a) Magnitude of F1 is greater than F2
(b) Magnitude of F2 is greater than F1
(c) Magnitude of F1 and F2 are equal
(d) Resultant net force in direction of F1

ANSWERS-
1.(c) Push as well as pull
2.(d) All of these
3.(b) Newton (N)
4.(a) Muscular force
5.(d) Magnetic force
6.(a) Electrostatic force
7.(a) Pressure
8.(b) Pascal (Pa)
9.(d)All of the above
10.(b) Increasing height of liquid
11.(b) Very high altitude like 8000 feet
12.(d) Sea level
13.(b) 2
14.(a) A
15.(c) B & C
16.(b) Magnitude of F2 is greater than F1 

HEAT Class- VII Chapter 4 C.B.S.E.

LEARNING OBJECTIVES- Knowledge of heat, temperature, thermometer and reading of temperature on thermometer, Differences between clinical and laboratory thermometers, Methods of transfer of heat – conduction convection and radiation, Understanding why woolen clothes are preferred in winter?, Understanding why white or light coloured cotton clothes are weared in summer?, why the base of utensils are made up of copper?

INTRODUCTION- Heat is a form of energy. Heat is accumulated inside any object when it is heated in fire. The heat is transferred from a hot object to cold object. The S.I. Unit of heat is Joule (J). Calorie and British thermal unit (BTU) are also used as units of heat.

Note-Watt (W) is a unit of rate of transfer of heat. The rate of transfer of one joule heat per second is called a watt.   

HOT AND COLD OBJECTS- If we eat or touch ice cream we feel cold. But the tea and handle of a girdle appear warm. If one liter warm water at 80˚C (degree Celsius) is mixed with one liter warm water at 50 ˚C then the temperature of mixed water becomes 65˚C . By touching we can say which is comparatively hot or cold.  But it is not always trustworthy. Temperature is used to measure the hotness or coldness of any object. The degree of hotness or coldness is called as ‘temperature’. Temperature is measured by a device called ‘thermometer’.

MEASURING TEMPERATURE- The temperature of any object is measured by thermometers. The thermometers are of different types-

1. Clinical thermometers –It is used to take temperature of humans. e.g. Glass and mercury thermometer, Digital thermometer, Infrared forehead thermometers etc.

2. Laboratory thermometers- It is used to take temperature of soil and chemicals in laboratories.

3. Maximum- minimum thermometers- They are used to measure temperatures of the day.

The range of temperature of glass and mercury clinical thermometer is 35˚C to 42˚C .It is because this thermometer is used for measuring human body temperature only.  The human body temperature does not go below 35˚C and above 42˚C. The average or normal body temperature is 37 ˚C. On this thermometer range remains given in degree Celsius as well as in Fahrenheit Scales.

There is a ‘kink’ near the bulb of clinical thermometer. This is a kind of bending of mercury line. It prevents the rising and falling of mercury level when taken out of mouth.

Fig.Kink in a clinical thermometer near bulb

ACTIVITY- READING OF CLINICAL THERMOMETER- Following are the steps and precautions in taking the reading of temperature through a clinical thermometer-

Fig. Clinical Thermometer

1. The Thermometer should be washed before and after use. Use of an antiseptic will be better.

2. It should be ensured before use that mercury level is below 35˚C.

3. Put the bulb of thermometer inside the mouth and gently close for 2-3 minutes.

4. Take out the thermometer and read the mercury level along the line of sight.

5. Do not hold the bulb of thermometer while taking the reading.

6. Glass and mercury thermometer should be handled with care otherwise it may break. The poisonous mercury may come out.

7. Clinical thermometers should not be kept near flame or in sunlight otherwise it may break.    

LABORATORY THERMOMETER-This thermometer is longer than clinical thermometer. It range of temperature is -10 ˚C to 110 ˚C . It is used to measure the temperature of chemical reactions, soil, water etc. It is used to take temperature in the chemical reaction, soil, water etc. in real time. It is because there is no ‘kink’. When it is taken out of the chemicals the mercury level falls so at the same time temperature is noted down.

Fig. Laboratory Thermometer

DIFFERENCES BETWEEN CLINICAL AND LABORATORY THERMOMETERS-

S.N.	Characteristic	Clinical Thermometer	Laboratory Thermometer
1.	Range	35 ˚C  to 42˚C	-10  ˚C  to 110 ˚C
2.	Kink	Present	Absent
3.	Length	Small	Longer than
4.	Used for	Humans , animals	Chemicals , Soil ,water etc

MODES OF TRANSFER OF HEAT- Heat is transferred from source to sink, surrounding or any other object. Heat is transferred from higher temperature object to lower temperature object. There are three modes of transfer of heat-

1. CONDUCTION- The process by which heat is transferred from hotter end to the colder end of an object is known as conduction. Conduction of heat occurs in solids. But, some solids are conductors of heat while others are insulators of heat.

Fig. Melting of wax due to conduction of heat

The materials which allow heat to pass through them easily are called conductors of heat. e. g. metals like iron, copper, aluminium etc. The materials which do not allow heat to pass through them easily are called insulators or poor conductors of heat. e. g- Plastic, wood, clothes, dry leaves, dry bricks etc. The pure water called as distilled water and dry air are insulators of heat (and current).

Example 1 when one end of a metal strip is heated with the flame of candle, the other end also becomes warm after some time. The wax pieces kept over it starts melting and falling. This activity confirms that heat is conducted through metals.

Example 2 One end of a steel spoon is inserted in a hot cup of tea. The other end becomes hot after sometime. It confirms that heat of hot tea has transferred from one end to other end. So, steel is a conductor of heat.

DIFFERENCES BETWEEN CONDUCTORS AND INSULATORS-

S.N.	CONDUCTORS	INSULATORS
1.	Allow heat to pass through them easily	Do not allow heat to pass through them easily
2.	Conductors are metals, mineral water, salty water, moist air etc.	Insulators are non-metals, dry wood, plastic, paper, clothes etc.

 

2. CONVECTION- The transfer of heat by movement of particles of medium being heated is called convection. Convection occurs in liquids, gases and fluids.

Example 1 On boiling the milk, the milk near the base of container gets hot due to flame. Hot milk rises up. The cold milk from the sides moves down towards the source of heat. This milk also gets hot and rises and comparatively cold milk from the sides move down. This process continues till the whole milk gets heated.

Fig. Boiling of milk by Convection

Example 2 A candle was lighted. One hand was kept above the flame and other on the side of flame. The air above top becomes warmer than the sides due to convection. So, the air above top will feel hotter by top hand than the air on side by side hand.

Fig.Transfer of heat by convection of air

Example 3 SEA BREEZE AND LAND BREEZE- The people living in coastal areas experience dual nature of blowing of air due to convection of heat. The sea breeze and land breeze blows in coastal areas. The sea breeze and land breeze are due to difference in heating of the land and ocean water.

During day, the land becomes warmer than the ocean. So, air near the land becomes warm and rises above. As a result a partial lackness of air or low density air pressure is created on the land during day due to sunlight. To full fill this lackness, air blows from sea toward the land. It is called as sea breeze.

Fig. Sea Breeze and Land Breeze

During night, the sea becomes warmer than land by releasing the heat absorbed during the day. So, the air above sea becomes warm and rises above. As a result a partial lackness of air or low density air pressure is created above the sea during night. To full fill this lackness, air blows from land toward the sea. It is called as land breeze.

 3. RADIATION- The process of transfer of heat from source to surrounding or other object with or without any medium is called radiation. In radiation the presence of any solid or liquid medium is not essential for transfer of heat.  All hot bodies radiate heat.

Example 1 The solar radiations (sunlight) reach to the earth through radiation method. The sunlight passes through vacuum (total absence of air) and then through air of atmosphere to reach on the earth.

Example 2 The heat reaches up to us when we are sitting in front of a room heater is an example of radiation of heat.

When heat is transferred to anybody, a part of heat is absorbed, a part of heat is reflected and a part of heat is transmitted. This is the reason during the hot sunny day the use of umbrella protects us because some part of sunlight is reflected, some part is absorbed and only some part of sunlight is transmitted. So, we feel comfort.

TYPES OF CLOTHES WE WEAR IN SUMMER AND WINTER- In summer season, white and light coloured clothes are weared to reflect the sunlight. So, the person wearing it can feel comfort in summer.

In winter season, black, dark and colorful clothes are weared so that sunlight can be absorbed and transmitted inside so that the person wearing it can feel comfort in winter season.

WHY WOOLEN CLOTHES KEEP US WARM- When we wear woolen clothes in winter we feel comfort due to checking of incoming of cold air inside and out going of our body heat. The woolen clothes entrap air inside it. Air is an insulator of heat, so neither the body heat is not released outside nor the cold waves come inside.

This is the reason that instead of one thick blanket, the two thin blankets joined together will give more comfort.

 SOLVED EXERCISE QUESTIONS-

Q.1 State similarities and differences between the laboratory thermometer and the clinical thermometer.

Ans-

Criteria	Clinical thermometers	Laboratory Thermometers
Similarities	It has mercury inside.	It also has mercury inside.
	Temperature Scale is degree Celsius (˚C).	Temperature scale is also degree Celsius.
Differences	It is used to measure temperature of the body.	It is used to measure temperature of water, chemicals
	Its range is 35 ˚C to 42 ˚C	Its range is -10 ˚C to 110 ˚C

    Q.2 Give two examples each of conductors and insulators of heat.

   Ans- Conductors-  1.  Copper      2. Aluminium

             Insulators-    1. Wood         2. Plastic

Q.3 Fill in the blanks:

(a) The hotness of an object is determined by its ………………

(b) Temperature of boiling water cannot be measured by a …………….thermometer.

(c) Temperature is measured in degree ………………………..

(d) No medium is required for transfer of heat by the process of ………………

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of …………………..

(f) Clothes of  ………………colours absorb heat better than clothes of lighter colours.

Ans-  (a) temperature             (b) clinical                        (c) Celsius   

          (d) radiation                 (e) conduction                   (f) dark

Q.4 Match the following:

(i) Land breeze blows during                                    (a) summer

(ii) Sea breeze blows during                                      (b) winter

(iii) Dark coloured clothes are preferred during    (c) day

(iv) Light coloured clothes are preferred during    (d) night

Ans-(i) –night       (ii)- day         (iii)- winter     (iv)- summer

Q.5 Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

Ans- The air is an insulator of heat. So, on wearing more layers of clothing during winter an insulation layer is created which prevents our body heat to go in surrounding and we feel comfort. This type of insulation layer is not formed if wear just one thick piece of clothing.

Q.6 Look at Figure. Mark where the heat is being transferred by conduction, by convection and by radiation.

 

 

 

 

 

Ans-

Fig. Showing- 1. Conduction 2. Convection  3. Radiation

 

 

Q.7 In places of hot climate it is advised that the outer walls of houses be painted white. Explain.   

Ans- White wall will reflect the sunlight and only little transmission occurs. So, such a wall will become comparatively less hot than the other coloured walls. The people living behind these walls in their room will feel more comfort.

Q.8 One litre of water at 30˚C is mixed with one litre of water at 50˚C. The temperature of the mixture will be

(a) 80˚C

(b) more than 50 ˚C but less than 80˚C

(c) 20˚C

(d) between 30˚C and 50 ˚C    

Ans-  (d) between 30˚C and 50 ˚C   

                           

Q.9 An iron ball at 40˚C is dropped in a mug containing water at 40˚C .The heat will

(a) Flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Ans-(b) not flow from iron ball to water or from water to iron ball.

 

Q.10 A wooden spoon is dipped in a cup of ice cream. Its other end

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of  convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Ans-(d) does not become cold

 Q.11 Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.

(b) such pans appear colourful.

(c) copper is a better conductor of heat than stainless steel.

(d)copper is easier to clean than stainless steel.

Ans- (c) copper is a better conductor of heat than stainless steel.

  

FORCE AND PRESSURE Class VIII Chapter 11 C.B.S.E.

 

INTRODUCTION OF FORCE- In our daily life we do a number of activities. These activities include push and pull of anything. Lifting, picking, throwing, pushing, striking, flicking, stopping, hoisting, shutting, opening, hitting, lowering, flying, Sliding, smashing etc. activities include push or pull. A push or pull acting on an object is known as force. Force is important to do every work. The direction of force will be the direction of push or pull applied on the object. The amount of force varies according to the type of work. The S.I. Unit of Force is Newton (N). The unit of force was given in honour of Sir Isaac Newton.

FORCE –A PUSH OR PULL- Lets understand force by a few more examples where push or pull is applied.

Activity 11.1- To Identify the actions as push or Pull Force

S.N.	TYPE OF ACTION	PUSH OR PULL FORCE
1	Lifting  a stone	Pull
2	Striking a coin of carom board	Push
3	Flicking a ball by hockey	Push
4	Opening the door of Car	Pull
5	Opening a drawer	Pull

 So, force of pull or push is needed in every kind of work.

Flicking the golf Ball (Push)

Lifting the Car (Pull)

FORCES ARE DUE TO AN INTERACTION- Suppose a man is standing behind a stationary car, the car will not move due to his presence. But, he pushes that car the car moves. It is due to applying a push force. Here, interaction between the car and man occurs.

Suppose a milkman is pulling his cow by a rope toward himself then it is an example of pull force. Here, interaction between the cow and the milkman occurs. 

Pull                  Force is due to interaction                Push  

EXPLORING FORCES-

Case I-When two girls are pushing a big box in a particular direction, it becomes easier for them to move the box. It is because both are applying the force in same direction and their forces are added.

Case II- When two girls are pushing the box from opposite side, the box will move in the direction of comparatively greater magnitude. In this case lower force will be deducted from greater force. So, deduction of forces occurs in this case.

The magnitude of force denotes its strength. It is expressed as │5│N. Here, magnitude of force in two vertical lines shows that strength is 5 Newton. Direction of the force is also important.

In case I the total strength of force will be   F₁ + F₂ = F

In case II the total strength of force will be   F₁ - F₂ = F       Where, F₁ > F₂

UNIT OF FORCE-The S.I. Unit of Force is Newton (N).  The smaller unit of force is dyne in CGS System.                     10⁵ dyne= 1 N

                             So,    1 dyne = 1 N /10⁵ = 10 ^_5 N

We Know that, Force (F) = Mass of an Object (m) x Acceleration (a)

                             Or, F = m. a   

If we put the units of mass and acceleration then the unit of force will be- Kg. m/s². This in short is called as 1 N (Newton).

 

A FORCE CAN CHANGE STATE OF A MOTION- When a football player kicks a stopped football, a force is applied to move in a particular direction. The state of rest of football changed. When the goalkeeper stops the kicked football, a force is applied. The state of motion of football changes to zero.

The speed of a moving vehicle increases when a force is applied on it in the direction of its motion. Similarly, the speed of moving vehicle decreases when the force is applied opposite to the direction of motion. So, the state of motion either increases or decreases due to applying the force.

 A FORCE CAN CHANGE DIRECTION OF A MOTION-When a goalkeeper dives to deflect the incoming ball, its direction changes. The direction of a ball changes when it strikes on a wall with an angle. The change in direction is opposite and with same angle.

 

A FORCE CAN CHANGE SHAPE OF AN OBJECT-Pressing down a lump of dough on a plate, pressing the spring, pulling an elastic rubber etc are examples of change in shape of objects due to force.

Change in shape  and size of  elastic rubber band

A force may bring following changes-

1. make an object move from rest.

2. change the speed of a moving object.

3. change the direction of a moving object.

4. change the shape of an object.

5. change some or all of the above effects together.

The application of force to bring change in shape, size, position or state of the object is not always applicable. e.g.- Even if you apply maximum on a wall, it will not move.  

TYPES OF FORCES-Some forces act on an object by other object when they are in contact with each other. Some forces act on an object by other object when they are not in contact with each other. On this basis there are two types of forces. Contact forces and non-contact forces.

A. CONTACT FORCES- Those forces which develop between two objects in contact are called contact forces. e.g.-

1. Muscular Force-The force resulting due to the action of muscles with an object is known as the muscular force. 

e. g.-The drought animals like oxen, horses, donkeys, camel, Yak etc. are used to perform a number of tasks like carrying, ploughing etc by applying muscular force.

Muscular Force of Animals and Humans 

e. g.-  The inhalation and exhalation of air from our lungs is due to movement of muscles. etc.

2. Frictional Force- The force which arises between two surfaces in contact is known as frictional force. Out of two at least one object should be in motion. If both the surfaces in contact are in motion then also friction will be there. For rough surface frictional force is greater than smooth surface.

The force of friction always develops in between moving surfaces in contact. The direction of force is opposite to the direction of motion.

Rough surface produces more friction than the smooth surface

e. g. Stopping of a moving ball on the ground by its own without any external force.

e.g. Stopping of a boat after some time  without sailing in still water.

e.g.- Burning of matchsticks on rough surface of match box. etc.

The frictional force produces heat. It is useful as well as a harmful force. When we walk, our energy is consumed more due to friction. But, friction helps us to not skid. A football,  cricket, tennis, sprinter like players wear spiked shoes to increase his/her friction so that skidding during running can be prevented.

 

B. NON-CONTACT FORCES- Those forces which develop between two objects without any contact are called non-contact forces. e.g.-

1. Gravitation Force- The attractive force which develops between the earth and any other object with or without contact on it is called gravitational force or force of gravity or simply gravity. Isaac Newton has discovered this force. All the objects have their own gravitational force. The gravity depends on the mass of objects and distance between them. The weight of an object varies from the Earth to the Moon. It is because of change in gravity. 

Earth Attracts all objects towards it. 

2. Magnetic Force- The fore exerted by a magnet on another magnet and magnetic substance is called magnetic force. Similar poles repel each other while dissimilar poles attract each other.

e. g. A magnetic force of attraction is found between dissimilar poles of two magnets.

N

S

         

         

N

S

   N – N = Repulsion

     S – S = Repulsion

       N-S = Attraction

e.g. A magnetic force of attraction is found between a magnet and iron.

Loadstone is a natural mineral that behaves like a magnet. Iron, cobalt and Nickel and their alloys are ferromagnetic. They are attracted towards the magnets.

3. Electrostatic Force- The force exerted by a charged body on another charged or uncharged body is called electrostatic force.

Electrostatic force of attraction

Electrostatic forces may be attractive or repulsive. Similar charges attract each other and dissimilar charges repel each other. Electroscope device is used to know the nature of charge present on anybody. Electrostatic force is also called as Coulomb force or Coulomb interaction.

PRESSURE- The force acting on a unit area of a surface is called pressure.

Pressure= Force/Area on which it acts

Unit of Pressure-   Newton (N)/m² or N.m^-2 Newton per square meter) = 1 Pascal

Pascal is S.I. derived unit. One Pascal is defined as one newton per square meter. Pascal was named after Scientist Blaise Pascal.

e.g.  When an iron nail is hammered with its pointed end into a wooden plank, it gets inserted easily. But, it is very difficult to insert that iron nail into wooden plank with its head. It is because the surface area of head is more than the pointed end. More is the force, more will be the pressure.  

e.g. The porters place a round piece of cloth on their heads to increase the surface area so that the pressure of luggage on a particular point on head can be reduced and distributed to comparatively bigger area. It helps the porters to carry luggage with better comfort due to reduced pressure.   

PRESSURE EXERTED BY LIQUIDS AND GASES- When any liquid is filled in a container, the liquid puts pressure on its walls.

e.g. A rubber sheet is fixed at one of the end of a transparent glass tube or plastic pipe. The pipe is kept in vertical position. The rubber sheet bulges out on pouring water. The bulging is more on pouring more water. So, it confirms that liquids exert pressure on the walls of their containers.

e.g. The fountains of leaked water in supply water pipes is because water is supplied with force. If any leakage or hole is there, water comes out with pressure.

ATMOSPHERIC PRESSURE- The pressure exerted by air is known as atmospheric pressure. Atmospheric pressure is very large which is counter balanced by our internal body pressure.

Let us imagine a unit area over our head which is filled with air in a very long cylindrical air column. If the area over our head is 15 c.m. X 15 c.m then an atmospheric pressure of 2250 N or 225 kg will be there.

e.g.- The rubber sucker pressed on a plane glass is very difficult to remove because the air inside it is almost removed after pressing. The outer air puts atmospheric pressure.

Partial vacuum and low air -pressure inside and high atmospheric pressure outside

SOLVED EXERCISE QUESTIONS

Q.1 Give two examples each of the situations in which you push or pull to change the state of motion of objects.

Ans- Examples of push to change state of motion-

1. Kicking a football

 2. Opening of doors

 Examples of push to change state of motion-

1. Opening a drawer

2. Drawing a bucket of water from a well

Q.2 Give two examples each of the situations in which applied force causes a change in the shape of an object.

Ans- 1.The shape of seat changes on sitting.

         2. The shape of lump of dough changes on pressing

Q.3 Fill in the blanks in the following statements.

(a) To draw water from a well we have to ……………………… at the rope.

(b) A charged body ………………………an uncharged body towards it.

(c) To move a loaded trolley we have to ………………….. it.

(d) The north pole of a magnet ……………………….the north pole of another magnet.

Ans- (a) pull    (b) attracts      (c) push or pull     (d) repels  

Q.4 An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on these information fill up the gaps in the following statements using the following terms.

muscular, contact, non-contact, gravity, friction, shape, attraction

(a) To stretch the bow, the archer applies a force that causes a change in its ………………

(b) The force applied by the archer to stretch the bow is an example of ……….. force.

(c) The type of force responsible for a change in the state of motion of the arrow is an example of a …………….. force.

(d) While the arrow moves towards its target, the forces acting on it are due to …………. and  that due to ………………of air.

Ans- (a) shape    (b) muscular   (c) contact   (d) gravitational force (gravity) , friction

Q. 5 In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

(b) Taking out paste from a toothpaste tube.

(c) A load suspended from a spring while its other end is on a hook fixed to a wall.

(d) An athlete making a high jump to clear the bar at a certain height.

Ans-

Agent exerting the force	Object on which it acts	Effects of the force
Fingers	Lemon	Change in shape of lemon and juice comes out
Fingers	Toothpaste tube	Change in shape of toothpaste tube and  paste comes out
Load	Spring	Stretching of Spring
Athlete’s  muscles	Pole	Change in athlete’s state of motion

 

Q.6 A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Ans- The muscular force of the blacksmith changes the shape of the piece of iron.

Q.7 An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

Ans- An electrostatic charge develops on inflated balloon due to rubbing by synthetic cloth. The force between charged inflated balloon and the wall is due to electrostatic force.

Q.8 Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion?

Ans- In this case, two forces namely ‘muscular force’ and ‘gravitational force’ acting on the plastic bucket containing water and held above ground by the hand. Muscular force is acting upward and gravitational force is acting downward. So, due to equal and opposite forces there is no change in the state of motion of the bucket.

   

Q.9 A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.

Gravity and Drag on Flying Rocket

Ans- Two Forces acting on the rocket are-

1. Gravitational force   

2. Atmospheric friction (drag)

Q.10 When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to

(a) Pressure of water

(b) Gravity of the earth

(c) Shape of rubber bulb

(d) Atmospheric pressure

Ans- (d) Atmospheric pressure