## Chapter 11 - Force and Pressure Extra Questions

Question 1: We know that there is a huge amount of atmospheric pressure on us. But we don’t experience its effect. Why?
We know that there is a huge amount of atmospheric pressure on us but we don’t experience its effect because the pressure inside our bodies is also equal to atmospheric pressure and cancels the pressure from outside.

Question 2: Why do sea divers wear specially designed suits?
Sea divers wear specially designed suits as the depth of the sea increases pressure increases. The pressure exerted by water deep under the sea is much greater than the pressure at sea level. These suits protect them from extreme pressure of water.

Question 3: On Lokesh’s birthday Shreya was given charge to amuse children with some little tricks. Shreya sticked balloons to the wall by just rubbing them in her clothes. She bent the water stream from a tap without touching it. She did so by bringing big balloon near to the flowing water. All children were very happy on seeing this little magic. Everybody praised Shreya.
• 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 is shown here?

• On rubbing the balloon with clothes, it get negative charge. The wall being positively charged gets attracted with balloon. Hence, the balloons stick to the wall.
• Negative charge on the balloon attracts positive charge on water molecules. Thus, bent the water molecules.
• Shreya is having scientific knowledge, and scientific aptitude.

Question 4: Observe the figures given below carefully.

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.

B > D > A > C
This is because the pressure of a liquid column depends upon the height of the liquid column and not on the volume of the liquid.

Question 5: It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
It is difficult to cut cloth using a pair of scissors with blunt blades because pressure is less.

Question 6: An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.
The archer shoots an arrow by stretching the bow string with muscular force. When the string is released, it reverts to its previous position, providing the initial force that drives the arrow horizontally. The downward force of gravity works on the arrow as a result the arrow eventually falls on the ground.

Question 7: Define force and give its standard units.
Force is the push or pull of an object. The standard unit of force is Newton, which has the symbol “N”.

Question 8: Name different types of forces. What is their basis of categorisation?
There are two types of force:
• Contact forces are forces exerted by one object on another when they are in contact with each other. Contact forces are of two types. They are: Muscular force and Force of friction (Friction or Frictional Force).
• Non-contact forces are forces exerted by one object another without any contact with each other. Non-contact forces are of three types. They are: Magnetic force, Electrostatic force and Gravitational force (Gravity or Force of Gravity).

Question 9: What are contact forces? Name the different types of contact forces.
Contact forces are forces exerted by one object on another when they are in contact with each other. Contact forces are of two types. They are: Muscular force and Force of friction (Friction or Frictional Force).
• Muscular force is the force exerted by the muscles of our body. We use muscular force for our various activities. Animals like bullocks, horses, camels, donkeys, elephants also use muscular force to perform various tasks.
• It is also known as Frictional Force and Force of Friction. Force of friction is the force which opposes the motion of an object over a surface.

Question 10: Why is it easier to walk on rough surface than on smooth surfaces?
It is easier to walk on a rough surface than on smooth surface because the rough surfaces have more irregularities than on smooth surfaces. And our foot has irregularities. This causes the friction to appear more in case of rough surface.

Question 11: Define the unit of pressure.
Pressure is the force acting on unit area of a surface. The SI Unit for pressure is pascal.
Pressure = Force/Area = N/m²
Unit = Nm²

Question 12: Can force act without an interaction between two objects? Give an example to explain.
The force may or may not act without an interaction between two objects. This is because forces like muscular force and frictional force need interaction to make effect of force on an object while forces like magnetic, gravitational & electrostatic forces needn’t require an interaction to make effects on object.
→ To kick a football, we need interaction between football and the foot.
→ A ball rolling on the ground gradually stops down after sometime due to interaction between ball and the ground.
→ An iron nail attracts to the magnets without any interaction.
→ Leaves get detached from plant and fall on ground without any interaction.
→ A plastic straw charged by rubbing with paper attracts a suspended plastic straw any interaction.

Question 13: What are the effects that force can produce? Give one example of each effect.

→ Force can make an object to make from rest. Example: If we apply push (apply force) the ball, it moves.
→ Force can stop a moving object. Example: Goal keeper applies force to stop moving ball.
→ Force can change the speed of an object if it is moving. Example: If the ball is moving and we push it the speed of ball will increase.
→ Force can change the direction of a motion of a moving object. Example: If the baller throws the ball (applies force), and then the batsmen hits the ball (applies force) the direction in which the ball is moving will change.
→ Force can change the shape of an object. Example: If we squeeze the tooth paste tube (apply force), then the shape of the tube will change.

Question 14: Differentiate between
a) contact and non-contact force
b) electrostatic force and magnetic force
c) force and pressure

a)
• Contact force
→ Contact forces are forces exerted by one object on another when they are in contact with each other.
→ Contact forces are of two types. They are: Muscular force & Force of friction (Friction or Frictional Force).
• Non-contact force
→ Non-contact forces are forces exerted by one object another without any contact with each other.
→ Non-contact forces are of three types. They are: Magnetic force, Electrostatic force & Gravitational force (Gravity or Force of Gravity).

b)
• Electrostatic force
→ Electrostatic force is the force exerted by a charged body on another charged or uncharged body.
• Magnetic force
→ Magnetic force is the force exerted by magnets.

c)
• Force
→ Force is the push or pull of an object.
→ Forces are due to interaction.
→ SI unit of force is Newton, symbol N.
• Pressure
→ Pressure is the force acting on a unit area of a surface.
→ SI unit of pressure is pascal, symbol Pa.