Class 8 Science Chapter 8 Question Answers - Force and Pressure

Q1: How do fluids exert pressure?
Ans: Fluids exert pressure in all directions. Fluids also exert pressure on the walls of the container that holds them.

Q2: Define pressure.
Ans: The force acting per unit surface area is called pressure. The SI unit of pressure is measured in Newton per square meter (N/m²), which is equal to 1 Pascal (Pa).

Q3: A force of 100 N is applied to an area of 4 m². Calculate the pressure being applied to the area.
Ans: Given: Force = 100 N, Area = 4 m²
Pressure = Force / Area = 100 N / 4 m² = 25 Pa.

Q4: Which force is responsible for the downward movement of a parachute? Will the person come down with the same speed without the parachute?
Ans: The force of gravity is responsible for the downward movement of a parachute. No, without the parachute, the person will come down with a higher speed because the parachute provides air resistance that slows down the descent.

Q5: Two Styrofoam balls held close to each other move away from each other. When they are released, name the force that might be responsible for this phenomenon. Explain.
Ans: The electrostatic force is responsible for this phenomenon. The two balls have similar charges, which causes repulsion between them, leading to their movement away from each other.

Q6: How does an applied force change the speed of an object?
Ans: If the applied force is in the direction of motion, the speed of the object increases. But if the force is applied in the direction opposite to the motion, then it decreases the speed of the object.

Q7: Name the forces acting on the car sticking to an electromagnet in a junkyard. Which one of them is larger?
Ans: The forces acting on the car sticking to an electromagnet are the magnetic force (in the upward direction) and the force of gravity or the weight of the car (downward). The magnetic force is larger than the force of gravity.

Q8: What is the similarity between electrostatic and magnetic forces?
Ans: The similarities between electrostatic and magnetic forces are:

• Both are non-contact forces.
• Both are attractive as well as repulsive forces.

Q9: What are the effects of force on an object?
Ans: The effects of force on an object include:

• Force can change the state of motion of an object.
• Force changes the speed of a moving object.
• Force can cause an object to turn or change direction.
• Force can change the shape of an object.

Q10: 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.

Q11: 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.

Q12: 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.

Q13: What is force? State the difference between contact force and non-contact force.
Ans:
Force is defined as any influence that can change the position, speed, and state of an object.

• Contact force: Force that can be applied only when it is in contact with an object is called a contact force, e.g., muscular force, frictional force
• Non-contact force: The force exerted on an object without touching it is known as non-contact force, e.g., gravitational force, magnetic force