Write true or false for each statement:
(a) The S.I. unit of force is kgf.
(b) A force always produces both the linear and turning motions.
(c) Moment of force = force x perpendicular distance of force from the pivoted point.
(d) Less force is needed when applied at a farther distance from the pivoted point.
(e) For a given thrust, pressure is more on a surface of large area.
(f) The pressure on a surface increases with an increase in the thrust on the surface.
(g) A man exerts same pressure on the ground whether he is standing or he is lying.
(h) It is easier to hammer a blunt nail into a piece of wood than a sharply pointed nail.
(i) The S.I. unit of pressure is pascal.
(j) Water in a lake exerts pressure only at its bottom.
(k) A liquid exerts pressure in all directions.
(l) Gases exert pressure in all directions.
(m) The atmospheric pressure is nearly 105 Pa.
(n) Higher we go, greater is the air pressure.
(a) False
Correct Statement — The S.I. unit of force is newton.
(b) False
Correct Statement — A force can produce either linear motion or turning motion.
(c) True
(d) True
(e) False
Correct Statement — Pressure is defined as thrust per unit area. Hence, for a given thrust, pressure is less on a surface of large area.
(f) True
(g) False
Correct Statement — A man exerts more pressure while standing than lying on the ground as area of contact is less in case of standing as compared to lying on the ground.
(h) False
Correct Statement — Incase of blunt nail, the thrust exerted on hammering acts on a larger area so less pressure acts on the piece of wood making it difficult to hammer the nail.
(i) True
(j) False
Correct Statement — Water in a lake exerts pressure in all directions.
(k) True
(l) True
(m) True
(n) False
Correct Statement — Higher we go, lesser is the air pressure.
Chapter Overview: Force and Pressure
This chapter covers the fundamental concepts of force and pressure for ICSE Class VIII. A force is a push or pull that can change the speed, direction, or shape of an object. Forces are classified as contact forces (muscular, friction, normal) and non-contact forces (gravitational, magnetic, electrostatic). Pressure is defined as force per unit area (P = F/A), measured in pascals (Pa). Students learn that smaller area produces greater pressure (sharp knife, drawing pin) and larger area reduces pressure (wide tyres, camel feet). The chapter also covers liquid pressure (P = hρg), atmospheric pressure measured by a barometer (76 cm Hg = 1 atm = 101,325 Pa), and Pascal’s law which states that pressure in an enclosed liquid is transmitted equally. Hydraulic machines (press, brakes, jack) work on Pascal’s law to multiply force.
Key Definitions & Concepts
| Term | Definition / Details |
|---|---|
| Force | A push or pull that changes the state of motion or shape of an object. Unit: newton (N) |
| Pressure | Force per unit area. P = F/A. Unit: pascal (Pa) = N/m² |
| Contact Force | Force requiring physical contact: muscular, friction, normal reaction |
| Non-Contact Force | Force acting at a distance: gravitational, magnetic, electrostatic |
| Atmospheric Pressure | Pressure exerted by the atmosphere. Standard: 760 mm Hg = 1 atm |
| Pascal’s Law | Pressure in an enclosed liquid is transmitted equally and undiminished in all directions |
| Hydraulic Machine | Device using Pascal’s law to multiply force. F1/A1 = F2/A2 |
Must-Know Points for Exams
- Force is measured in newtons (N). 1 N is the force needed to accelerate 1 kg by 1 m/s².
- Pressure = Force / Area. More area means less pressure for the same force.
- Liquid pressure increases with depth: P = h × ρ × g.
- Atmospheric pressure = 76 cm Hg at sea level.
- Pascal’s law allows small forces to produce large forces in hydraulic machines.
- Examples of high pressure: sharp knife, needle, nail. Low pressure: wide tyres, snowshoes, camel feet.
Quick Self-Test
- Define the main concept of this chapter in one sentence.
- List the key types or categories discussed in this chapter.
- Give three real-life examples related to the main concept.
- Draw and label the key diagram of this chapter from memory.
- State the main law or principle covered in this chapter.