Class 8 Science Chapter 8 HOTS Questions - Force and Pressure

Q1: We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why?
Ans: The pressure of air inside our body is same as that of the atmosphere. Therefore, we do not experience its effect.

Q2: Why do sea divers wear specially designed suits?
Ans: Since the pressure of liquid increases with the increasing depth of sea. Specially designed suits protect scuba divers from the huge pressure of the water underneath.

Q3: Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied?
Ans: Both the persons are applying forces from opposite direction with equal magnitudes.

Q4: 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.
Ans: The initial force is muscular force which sets the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.

Q5: Two rods: A and B, having same weight and equal length have different thickness. Rod A is thinner while Rod B is thicker. They are held vertically on the surface of sand. Which one of them will sink more? Why?
Ans: Rod A will go deeper as it has a smaller area of contact, therefore the same force produces more pressure. In case of rod B the same force produces less pressure.

Q6: It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
Ans: Blunt blades have larger area compared to the sharp-edged blades. Thus, the applied force produces a lower pressure in case of blunt blades, which makes it difficult to cut the cloth.

Q7: 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.
Ans: Pressure of a liquid column depends upon the height of the liquid column and not on volume of the liquid. Decreasing order of pressure at the base of each vessel is B > D > A > C.

Q8: 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?

Ans: 

• On rubbing the balloon with hair or clothes, it acquire negative charges. The negative charges are attracted to the positive charges on the wall and balloon sticks to the wall.
• Negative charge on the balloon attracts positive charge on water molecules. Thus, bent the water molecules.
• Shreya is dutiful, friendly with scientific aptitude.

Q9: What is force? State the difference between contact force and non-contact force.
Ans:

Q10: Define the different types of forces.
Ans: Force can act on a body from a distance or by being in contact with it. Depending on this, forces can be classified as contact and non-contact forces.

• Contact forces: When force is applied on an object by direct or indirect physical contact the applied force is called contact force. Muscular and frictional force are example of contact force.
  • Muscular force: The force resulting due to the action of muscles is known as the muscular force.
  • Frictional force: The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
•  Non-contact forces: When a force is applied to an object by another body that is not in direct contact with it is called non-contact force. Gravitational, magnetic and electrostatic force are example of non-contact force.
  • Gravitational force: The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity.
  • Electrostatic force: The force exerted by a charged body on another charged or uncharged 1 body is known as electrostatic force.
  • Magnetic force: The force exerted between a magnet and other magnet or magnetic material is known as magnetic force.

Q11: Why it is easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)?
Ans: A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the ‘flat’ shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.

Q12: What is pressure? What is the relation of pressure with area on which it is applied?
Ans: Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we can conclude that pressure increases with decrease in area. List the characteristics of pressure exerted by a liquid.

• Liquid exerts pressure in all directions.
• Pressure in liquid does not depends on shape, size and surface area of the container.
• Pressure increases with depth.
• All points at the same level in a liquid are at the same pressure.
• Pressure does not depend on the surface of the immersed object.