The correct option is (d) 1, 2, 3 and 4.
Explanation
Pressure is defined as the force acting perpendicularly on a unit area of a surface. The mathematical relationship is given by:
Pressure (P) = Force (F) / Area (A)
This indicates that pressure is inversely proportional to the surface area over which the force is applied. Consequently, for a given force, a smaller area results in higher pressure, while a larger area results in lower pressure.
Statement-wise Analysis
- Statement 1 is Correct: School bags are designed with wide straps to increase the surface area in contact with the shoulders. By increasing the area (A), the pressure (P) exerted by the weight of the bag is reduced, preventing injury and discomfort to the student.
- Statement 2 is Correct: A sharp knife has a very thin cutting edge, which significantly reduces the surface area of contact. When force is applied, this small area generates high pressure, allowing the knife to slice through vegetables with minimal effort.
- Statement 3 is Correct: Camels possess broad feet which provide a large surface area in contact with the ground. This increased area reduces the pressure exerted by the camel's weight on the sand, preventing the feet from sinking and facilitating movement in the desert.
- Statement 4 is Correct: Tractors are heavy vehicles often operated on soft soil or mud. They are fitted with wide tyres to maximize the area of contact with the ground. This distribution of weight over a larger area reduces pressure, preventing the tyres from sinking into the soil.
Key Takeaway
The effect of a force depends on the area over which it acts. To facilitate piercing or cutting, surface area is minimized to increase pressure. Conversely, to support heavy loads on soft surfaces or reduce physical stress, surface area is maximized to decrease pressure.