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The correct answer is:

N m

When we suck air in the straw, the pressure of the air in the straw becomes less than that of the outside air on the cold drink or fruit juice in the bottle (or the glass). Hence, the cold drink or fruit juice rises in the straw and enters our mouth. We can then drink it. There is no atmosphere on the moon. Hence, it is not possible to enjoy a cold drink or fruituice on the moon by using a straw.

Pressure = Thrust / Area

Contact Forces: 

(i) Pushing of a pile of rubble by a bulldozer. 

(ii) Squeezing of a gum tube to extract the gum. 

Non-contact Forces: 

(i) When a magnet is brought near iron-nails, they stick to the magnet. 

(ii) A ripen apple falls by itself from the tree. 

When an aeroplane descends at a high speed, there is an increase in air pressure. This increases the pressure on the ear drum. Hence, some people have earache when they travel by an aeroplane.

The tendency of an object to remain in its existing state is called its inertia.

The tendency of an object to remain in its existing state is called its inertia

If we open or shut a door, we need to apply less force at the free end because according to the formula of moment of force 

M = Force × Perpendicular distance of force from axis of rotation

Magnitude of force is inversely proportional to the perpendicular distance of force from axis of rotation. Thus, as the distance between the point of force application and hinge will increase, the amount of force required to open the door will decrease.

True Less force is needed when applied at a farther distance from the pivoted point.

No, the body will not rotate as

Turning effect = Force x ⊥ of the force from the pivoted point.

= Fx 0 = 0

⊥ distance = O or force is parallel to the point of application of force.

Force(F) = 80N

Perpendicular distance = 1.75m

∴ Moment of force = F x perpendicular distance

= 80 x 1.75 = 140Nm.

The ink in a fountain pen (filled at sea level at atmosphere pressure) may come out through its mouth while travelling by air if the outside pressure becomes less than the pressure in the ink holder of the pen. This can spoil the clothes/purse/bag. Hence, people are often advised not to carry fountain pens while travelling by air.

Pressure = Force / Area

Force = Pressure × Area

= 50,000 x 0.05 = 2,500 Newton

Pressure = \(\cfrac{Force}{Area\,on\,which\,the\,force\,in\,applied}\)

1 bar = 10⁵ N/m² .

1 atmosphere = 101 × 10³ Pa.

applying the force farthest from the pivoted point.

Fountain pens are built in such a way that the pressure inside them balances the atmospheric pressure at sea level. Since atmospheric pressure decreases with an increase in height above sea level, the pressure inside the pen turns out to be much greater than the air pressure in an aeroplane and the pen starts leaking.

Force can change the static condition of a body. 

1. If you squeeze a sponge, its shape changes. 

2. If you pull a rubber band, it becomes longer.

The SI unit of density is kg/m³

The SI unit of pressure is N/m² .

Clockwise moment of force—When the moment of force is in the clockwise direction.

Anticlockwise moment — When the moment of force acts in an anticlockwise direction.

For a given object, the buoyant force in liquids of different density is the same.

Force can change the static condition of a body. 

1. A rest rubber ball begins to move, when a force applied on it. 

2. Player applies a force on the stationary football while taking a penalty kick is football match. The force applied by player makes the football move towards the goal.

Pressure deep under the sea is so high that if the divers don't wear specially designed suits, the water pressure will crush their body.

⊥ Distance = 10cm = 10/100 = 1/10 m

Force applied on spanner 5 N

∴ Moment of force = F ×⊥ distance

= 5 × 1/10 = 0.5 nm

The density of a substance is the ratio of its mass to volume.

The SI unit of density = \(\cfrac{the\,SI\,unit\,of\,mass}{the\,SI\,unit\,of\,volume}\) = kg/m³

[Note: Density is useful in determining the purity of a substance. The CGS unit of density is g/cm³ . 

1 kg/m³ = 10³ g/(100 cm)³ = 10^-3 g/cm³ 

∴ 1g/cm³ = 1000 kg/m³}

Barometer is used to measure the difference in the liquid pressure.

The air pressure on our body is equal to the atmospheric pressure.

If the force is removed completely when an object acquires a certain speed, the object will move with the velocity it has at the instant the force is removed. 

For example, a body moving with constant speed along a circular path in a horizontal plane will fly tangentially in the sense of motion if the centripetal force (the force directed towards the centre of the circle) is removed completely.

EXPERIMENT: Take a tin-can having an airtight cap (screw cap). Remove cap and boil some water in it, so that steam comes out and in this way air from inside goes out. While boiling replaces the cap and allows it to cool. Vapors inside condense and form water creating a vacuum above them. We see the can crumbles due to air pressure from outside. This proves that air exerts pressure.

Honey has greater viscosity. 

Reason : Thicker liquids are more viscous than thinner liquids. As honey has greater viscosity, more frictional force will be acting on it.

1. Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive force of the surface layer.

2. In the absence of other force including gravity drops of virtually all liquids would be approximately spherical.

Static friction, Rolling friction , Sliding friction.

The SI unit of force is the newton.

F = 20 N           ⊥ distance = 0.5 m

Moment of force = Force x perpendicular distance of force from the point of rotation

= F x ⊥ distance

= 20 N × 0.5 m

= 10Nm

(a) Atmospheric pressure which is more than inside pressure of balloon causes the balloon to collapse. 

(b) Atmospheric pressure acting from outside the dropper balances the pressure exerted by water and water does not come out of a dropper. On pressing the dropper inside pressure of water becomes more than outside atmospheric pressure and water runs out. 

(c) Two holes are made in a sealed can so that ATMOSPHERIC AIR presses the oil at one hole and oil comes out of the second hole.

For a given volume, the surface area of sphere is the minimum. This is the reason for the liquid drops to acquire a spherical shape.

Correct answer is (b) Poise

1. True

2. True

3. True

4. True

5. False - Rolling friction is slightly lesser than the sliding friction.

6. True

7. True

8. False - using barometers, one can measure the atmospheric pressure.

9. True

10. True

1. By using lubricants: These are applied to surfaces to reduce the friction between the surfaces. Example Oil, wax, grease and castor oil. 

2. With the help of polishing the surface: We sprinkle fine powder on the carrom board and then we polish its surface to make smooth so that the striker slides easily on the surface.

3. By using ball bearing: We use leadshots in bearing of a cycle hub because rolling friction is smaller than sliding friction.

(d) Both (a) & (b)

Given : 

Weight of a stone F = 500 No. 

Area A = 25 cm² = 25 x 10^-4 m² 

To find : Pressure P = ?

Pressure P = 20 x 10⁴ N/m² (or) 20 x 10⁴ Pa

1. Water can travel to great heights inside plants. Water moves up the xylem through a process called capillary action.

2. During transpiration, water evaporates from holes in the surface of leaves into the air. As leaves, they attract the water molecules still in the plant, helping to pull water up through the stems from the roots.

1. Increases

2. Pascal's Law

3. Surface tension

4. Torricelli

Correct answer is (b) Newton

1. Decreases

2. Equal 

3. Atmospheric 

4. Less 

5. Nature

(c) Both (a) & (b)

(a) stop moving

Friction : Friction is a force that shows down moving objects or prevents stationary objects from moving. 

Examples of the utility of friction in day to day life.

• Cars and buses are able to move safely on the road because of friction between the treaded tyres and the surface of the road. 
• We are able to write on paper only with the help of friction between the pencil or pen and paper.