PROPERTIES OF MATTER
The Properties of Matter course explores the fundamental characteristics that define and distinguish materials, focusing on both physical and mechanical attributes. Key concepts include density, which explains why oil floats on water; pressure, as seen in how sharp knives cut more effectively due to higher pressure over smaller areas; and elasticity, which is crucial in designing springs and shock absorbers. The course also covers floatation using Archimedes’ Principle, which helps explain how ships float despite their massive weight. Additionally, it examines surface tension, observable when insects like mosquitoes walk on water, and viscosity, which influences the flow of engine oils in automobiles.
2. PRESSURE
1.2 Pressure
A fluid (liquid or gas) exerts pressure on the walls of its container, or on any surface with which it is in contact. A big force on a small area produces a high-pressure
Pressure is defined as the normal force acting per unit cross-sectional area.
pressure = normal force/cross-sectional area p = F/A
Force is measured in newtons and area is measured in square metres. The units of pressure are thus newtons per square metre (Nm−2), which are given the special name of pascals (Pa).
1Pa = 1Nm−2
1.2.1 Examples
1. A chair stands on four feet, each of area 10cm2. The chair weighs 80N. Calculate
the pressure it exerts on the floor.
2. A rectangular water tank of weight 4.5 x 103N measures 2.0m by 1.5m by 1.2m. Calculate the minimum pressure it can exert when resting on a horizontal surface.
3. A rectangular block of dimensions 2.0mxl.0mx0.5m weighs 200N. Calculate the maximum pressure exerted by the block on a horizontal floor.
4. A rectangular tank contains water to a depth of 2m. If the base is 4m x 3m calculate the force on the base. (Density of water = 103kgm3, g=10ms-2)
5. The pressure exerted on the floor by a boy standing on 4 Feet. If the weight of the boy is 40kg. Assuming each shoe's contact area is 6cm by 25cm (Take 1kg wt = 10N).