Short type answer Questions, Force and Pressure

ICSE Class 8 Physics
Force, Moment of Force, Thrust & Pressure

Short Type Answer Questions

1. Define force. State its SI unit.

Force is a push or pull which changes or tries to change the state of rest or motion of a body.
SI Unit: newton (N)

2. State two effects of force.

1. Force can change the speed of a body.
2. Force can change the shape or size of a body.

3. How does force affect a rigid and a non-rigid body?

Rigid body: Force changes its state of motion.
Non-rigid body: Force changes its shape or size.

MOMENT OF FORCE

4. Define moment of force.

The turning effect produced by a force about a fixed point or axis is called moment of force.

5. State the SI unit of moment of force.

newton metre (N m)

6. State two factors affecting moment of force.

1. Magnitude of force.
2. Perpendicular distance of force from the axis of rotation.

7. Write the formula for moment of force.

Moment of Force = Force × Perpendicular Distance
M = F × d

8. How can the moment of force be decreased?

By reducing the force or decreasing the perpendicular distance from the axis.

9. How can a greater moment of force be obtained?

Apply a larger force or increase the perpendicular distance from the axis.

10. What are clockwise and anticlockwise moments?

If a force tends to rotate a body in the clockwise direction, it produces a clockwise moment.
If it tends to rotate in the anticlockwise direction, it produces an anticlockwise moment.

THRUST

11. What is thrust?

The force acting normally (perpendicularly) on a surface is called thrust.

12. State the unit of thrust.

newton (N)

13. On what factor does the effect of thrust depend?

It depends on the area over which the thrust acts.

PRESSURE

14. Define pressure and state its SI unit.

Pressure is the thrust acting per unit area.
Pressure = Thrust / Area
SI Unit: pascal (Pa)

15. How is thrust related to pressure?

Pressure = Thrust ÷ Area

16. Name two factors on which pressure depends.

1. Thrust applied.
2. Area of contact.

17. Why is the foundation of a building made wider?

A wider foundation increases area and reduces pressure on the ground, making the building stable.

18. Why is it easier to cut with a sharp knife than a blunt knife?

A sharp knife has a smaller area of contact and therefore produces greater pressure.

19. A gum bottle rests on its base. If placed upside down, how do thrust and pressure change?

Thrust remains the same because weight remains the same.
Pressure increases because the area of contact decreases.