# RBSE Solutions for Class 7 Science Chapter 12 Pressure

## Rajasthan Board RBSE Class 7 Science Chapter 12 Pressure

RBSE Solutions for Class 7 Science ### RBSE Class 7 Science Pressure Intext Questions and Answers

Page No 114.

Question 1.
What is pressure?
The perpendicular force applied per unit area on any object is called pressure.

Page No 115.

Question 2.
Why does the nail penetrate into wooden block by striking hard with hammer?
Due to the hard strike by the hammer. more force is applied due to which more pressure is applied on the object. So it penetrates into wooden block easily.

Question 3.
How is pressure dependent on area?
The value of pressure applied on any object depends on the applied force and contact area of object. When contact area is reduced, pressure increases. Question 4.
Two balloons are filled with air. Puncture one balloon through flat head of pin and puncture the second balloon through sharp head of the same pin. In which situation was the balloon punctured easily?
The balloon is punctured by sharp pin head easily because the value of pressure depends on the contact area of object. When contact area is reduced, pressure increases. Here the sharp head of pin has less surface area in caparison to flat head of pin, so pressure increases and balloon is punctured easily.

Question 5.
We put two bricks on two sponges (one is flat in length and other is vertical in position). Which brick more squeezes sponges?
We see that sponge is squeezed more in vertical position of brick than the other one. Here the applied force is equal on sponge in both situations, but there is less surface area in vertical position of brick. So pressure becomes higher and sponge is squeezed more.

Page No 116.

Question 6.
Does air apply pressure on an object?
Yes, air apply pressure on an object.

Question 7.
Why does the plastic bottle collapse when the cold water is poured on vacated & tightly capped bottle which was previously filled with boiled water.
After draining the hot water from bottle, water vapours are trapped inside the bottle. When cold water is poured on the bottle then water vapours cool into liquid so the amount of water vapour inside the bottle reduces, thus the resultant pressure also reduces and the bottle collapses due to external air pressure.

Page No 117.

Question 8.
Does liquid apply pressure like air?
Yes, Liquid also applies different pressures in different conditions.

Page No 119.

Question 9.
Do objects have equal weight in air or water?
No, Weight of objects is reduced inside water.

### RBSE Class 7 Science Pressure Text Book Questions and Answers

Question 1.
The unit of pressure is –
(a) Newton
(b) Meter per second
(c) Newton/Meter2
(d) Joule
(c) Newton/Meter2

Question 2.
As the height of liquid in a column increases, the amount of pressure will be –
(a) Less
(b) More
(c) No change
(d) Length
(b) More Question 3.
The spring balance is used to measure –
(a) Work
(b) Weight
(c) Speed
(d) Length
(b) Weight

Fill in the blanks with suitable words:

1. As we move from the earth’s surface to a higher altitude, air pressure will be …………………..
2. The force acting upon objects immersed in a liquid is called …………………..
3. Pascal is unit of …………………..

1. Decreased
2. Buoyant force
3. Pressure

Question 1.
Define pressure.
The perpendicular force applied per unit area on any object is called pressure. Question 2.
Why is the knife used for cutting vegetables sharper?
Pressure depends on surface area of the object being pressed. Hence, when contact area is less, pressure will be high. So the knife used for cutting vegetables is sharper. It decreases surface area of the knife, consequently more pressure is exerted even for less force is applied and vegetables can be cut easily.

Question 3.
What will be effect on pressure as area increases?
Value of pressure applied on object depends on applied force and its contact surface area. If contact area is less, then pressure will be high or vice-versa.

Question 1.
Explain the importance of atmospheric pressure in daily life.
Pressure exerted on us b’ surrounding atmosphere is called atmospheric pressure. Atmospheric pressure is very important in our daily life. Air flows from high pressure area to low pressure area. So, we can say that air blows due to the difference in air pressure. Due to this clouds formed, rain becomes, season changes and temperature is controlled. We can breathe is appropriate air pressure. Question 2.
What do you mean by buoyant force? The buoyant force is equal to the weight of the displaced liquid, prove it by an experiment.
Buoyant force:
An upward force acts on an object when it is inside water. It reduces some weight of the objects. This loss in weight is equal to weight of the liquid displaced. It is known as buoyant force and this property of hquids is called buoyancy.

Experiment:
Take a stone. Clamp it with thread on balance and measure its weight (W), from the markings of the balance. Now, put it into a pot filled with water and measure its weight, W’, from the balance. Deduct the weight of the object in air from W’ in water and calculate the weight loss.

Now, collect the displaced water into a measuring cylinder and take the weight of displaced water. We will find the weight of displaced water by the object is equal to its weight loss (W-W). This value is equal to buoyant force exerted on the object. So, Buoyant force = Weight of displaced liquid by an object.  Question 3.
Liquids also exert pressure as does air. Explain it.
Liquid applies pressure on the walls of a pot. To understand it, let us perform an activity Liquids also apply pressure as does air. Experiment:
Take a balloon and fill it with water gradually. The balloon expands slowly. The expansion of balloon in all directions with increased amount of water shows that liquid applies pressure on the walls of a pot.

### RBSE Class 7 Science Pressure Important Questions and Answers

Question 1.
In the following what is called newton per meter square –
(a) Joule
(b) Pascal
(c) Hertz
(d) None of these
(b) Pascal

Question 2.
What is the average value of atmosphere pressure at sea level?
(a) 101325 Pascal
(b) 101225 Pascal
(c) 101125
(d) 101425 Pascal
(a) 101325 Pascal Question 3.
How is the value of water pressure at points in horizontal plane at equal height?
(a) Same
(b) different
(c) less in left, more in right
(d) None of above
(a) Same

Question 4.
How the value of liquid pressure changes with depth
(a) decreases
(b) increases
(c) a & b both
(d) No change
(b) increases

Question 5.
As we move towards height. air pressure becomes –
(a) Less
(b) More
(c) unchanged
(d) less & more both
(a) Less

Question 6.
In what way liquid pressure changes by increasing height of liquid column?
(a) Increases
(b) decreases
(c) remain unchanged
(d) None of these.
(a) Increases Question 7.
The value of buoy ant force is –
(a) Less than weight of liquid displaced by object
(b) Equal to the weight of liquid displaced by object
(c) More than the weight of liquid displaced by object.
(d) All the above
(b) Equal to the weight of liquid displaced by object

Question 8.
On going at height, atmospheric pressure –
(a) increases
(b) decreases
(c) remain unchanged
(d) None of these
(b) decreases

Fill in the blanks:

1. Air exerts ……………………………… on all objects. (Pressure/motion)
2. ……………………………… per unit area is called pressure. (force / pressure)
3. Liquids also apply ……………………………… as does air. (Pressure / no pressure)
4. Liquid pressure ……………………………… with the increase in the height of the liquid column. (increases / decreases)
5. B keeping the value of force constant, more pressure will be applied for ……………………………… (less area / more area)

1. Pressure
2. Force
3. Pressure
4. Increases
5. Less area.

Match the column I with column II:

Question 1. 1. (b)
2. (a)
3. (d)
4. (e)
5. (c).

Question 1.
What is the unit of pressure?
Newton per meter square is the unit of pressure. It is also known as Pascal.

Question 2.
On what pressure applied on an object depends?
Pressure applied on an object depends on contact surface area of the object and value of force.

Question 3.
On what value of pressure depends?
Value of pressure depends on applied force.

Question 4.
What is Pascal?
it is unit of pressure which is equal to newton per meter square. Question 5.
What is called air pressure?
It is the applied force on one meter square surface area. (by air).

Question 6.
Where air exerts pressure?
Air applies similar pressure ¡n all directions at each spot.

Question 7.
In which directions air applies pressure?
Air applies pressure in all directions.

Question 8.
What is the value of average atmospheric pressure at sea level?
It is 101325 Pascal.

Question 9.
What is called atmospheric pressure?
Pressure exerted on us by surrounding atmosphere is called atmospheric pressure.

Question 10.
In which direction air flows based on atmospheric pressure?
Air flows from high pressure area to loss pressure area.

Question 11.
Why air flows?
Air is blown due to atmospheric pressure difference

Question 12.
Where liquid exerts pressure?
Liquid exerts pressure on the walls of the pot in which it is kept. Question 13.
What effect is observed on the value of liquid pressure by increasing height of column of liquid?
By increasing height of liquid column. value of liquid pressure is also increased.

Question 14.
What happens on the value of liquid pressure by increasing liquid depth?
The value of liquid pressure increases. with increasing depth.

Question 1.
Write the formulae of pressure?
Pressure:
it is the perpendicular force applied on unit surface area of the object. It can be expressed as – Pressure depends on contact surface area and force applied on the object. Question 2.
Air applies pressure on object. Explain with experiment.
Air applies pressure on object:
Experiment:
Take water in pot and heat till it boils. Pour this boiled water into a plastic bottle. After sometime. drain water from the plastic bottle and tightly cap the bottle. Now, the cold water is poured on bottle. We see that bottle collapses. It is because after draining the hot water from bottle. water vapours are trapped inside the bottle.

When cold water is poured on the bottle. then water vapours cool into liquid so the amount of water vapour inside the bottle reduces, thus the resultant pressure also reduces and bottle collapses due to external air pressure Thus we can say that air has pressure.

Question 3.
What is called buoyant force and buoyancy?
An upward force acts on objects submerged in liquid which is known as buoy ant force. This property of liquids is called buoyancy.

Question 4.
Sometimes tin-sheds or khaprels are blown away from weak homes. Why this happens?
Air flows from high pressure area to low pressure area. So. we can say that air blows due to the difference in air pressure. When air blows with speed. the air pressure is reduced on the roof but air pressure increases inside the rooms. Due to this tin-sheds or khaprels are blown away from weak homes. Question 5.
The value of water pressure is equal at points in horizontal plane at equal height. Explain with an experiment and diagram.
Experiment:
Fill a plastic bottle with water. Make holes A. B. C at equal height on it using a needle. close these holes using a tape. No remove the tape from hole A for one minute and collect water into measuring glass and measure the amount of withdrawn water. Repeat the same process with hole B and C. sec that amount of withdrawn water from three holes is equal in quantity. So. it is clear that the value of water pressure is equal at points in horizontal plane at equal height. Question 6.
How pressure inside our body balances the air pressure exerted on us?
Approximately fifteen thousand kilogram force is applied on human body by atmospheric pressure. Even then our body does not shrink because pressure inside the body balances the atmospheric pressure.

Question 7.
Why the walls of dams are constructed wider at the bottom and narrower towards the above part?
Liquid has more pressure at greater depth. To bear this increase in pressure. the walls of dams arc constructed wider at the bottom and narrower towards the above part.

Question 8.
Why the water tank is built at a greater height?
For water distribution, the water tank is built at a greater height so that water can be easily distributed at greater heights When water comes from height. than water pressure becomes high which increases speed of water in large.

Question 9.
As we go at increasing heights, we feel difficulty in breathing. Why?
As we go at increasing heights, the air pressure is reduced. Due to this we feel difficulty in breathing. Except this. there is less amount of oxygen at greater, heights. so sometimes we need artificial respiration.

Question 10.
What is difference between force and pressure? State
Differences between force and pressure are as follow – Question 11.
What are the laws of liquid pressure?
Laws of liquid pressure are as follows –

1. The liquid pressure at any point is same inside constant liquid in all directions.
2. The value of Liquid pressure is equal at points in horizontal plane at equal height.
3. Liquid pressure increases with the increase in the height of the liquid column.
4. Pressure exerted on any point of the liquid, is distributed uniformly inside the Liquid.

Question 12.
We feel difficulty in walking on sand in desert but camel can walk easily on sand. Why?
The contact surface area of sole of our foot is less and so whole body weight creates more pressure so that our legs begin to sink in sand. While in case of camel. it has large surface area of Its legs which reduces pressure so its legs do not sink into the sand. Hence a camel can walk easily on sand. Essay type Questions:

Question 1.
Explain the dependence of pressure on force with an experiment.
Experiment Place the sharp head of a nail towards a wooden block and strike it lightly by hammer. Nail does not pierce the wooden block by light blow of the hammer. Using same hammer. now strike hard. The nail penetrate into wooden block this time. It is clear from both the above activities that magnitude of pressure depends on applied force. When the applied force is different on the same area then the pressure is also different on the object.

Question 2.
Explain with diagram the dependence of pressure on surface area by an experiment.
Experiment:
Put a brick on sponge as shown in figure Now put the brick vertical on sponge. The applied force is equal on sponge in both situations, How ever We sec that sponge squeezes more in vertical position of brick. It is because brick in vertical direction has less surface area than in flat situation.

So. if the area is reduced and value of force is kept constant then pressure becomes high. This is the reason why sponge squeezes more in vertical position of brick. We can say that he value of pressure depends on force and the contact area of object. When contact area is reduced. pressure increases. P = F/A (P Pressure. F = Force. A Constact Area) Question 3.
By an experiment and a diagram explain that liquid pressure increases with the increase in the height of the liquid column.
Liquid pressure increases with the increase in the height of the liquid column:

Experiment :
Tie a rubber sheet of balloon on one side of glass tube as shown in figure. Fill the tube with water partially. Due to pressure exerted on balloon, balloon expands a little. As we increase water level in the tube. we sec that balloon expands more. So we can say that liquid pressure increases with the increase in the height of the liquid column. Question 4.
Liquid pressure increases with increase in depth. Explain with diagram by an experiment.
Experiment:
Take a plastic bottle and make three same sized holes A. B. C at different heights and close them with a tape as in figure. Fill the plastic bottle with water. Put it on a stool. open all the three holes simultaneously and observe the water coming out of the holes. We see that the height of the water column above hole A is less i.e.. the depth from surface is less whereas the height of the water column above hole C is more. Due to low pressure at hole A. water drops at a shorter distance and due to high pressure at hole C. water drops at a greater distance. Thus liquid pressure increases with increase in depth.

Question 5.
Give some interesting examples. about pressure observed in daily life.

1. School bag strips that hang on shoulder are made broad so that low pressure is exerted on the shoulders.
2. Camel can walk easily on sand due to large surface area of camels foot which reduce pressure and its legs do not sink into the sand.
3. Liquid has more pressure at greater depth. To bear this increase in pressure. the walls of dams are constructed wider at the bottom.
4. As go at increasing heights the air pressure is reduced. Due to this we feel difficulty in breathing.
5. For water distribution, the water tank is built at a greater height so that water can be easily distributed at greater heights.
6. Approximately fifteen thousand kilogram force is applied on human body by does not shrink, because pressure inside the body balances the atmospheric pressure. Question 6.
Explain the reasons –

1. Why divers bear a metallic sheath during diving in sea?
2. Why the types of heavy vehicles are broader?