Published on Jan 07, 2019

The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Definitions of mass often seem circular because it is such a fundamental quantity that it is hard to define in terms of something else. All mechanical quantities can be defined in terms of mass, length, and time. The usual symbol for mass is m and its SI unit is the kilogram. While the mass is normally considered to be an unchanging property of an object, at speeds approaching the speed of light one must consider the increase in the relativistic mass. The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume.

To observe and compare the pressure exerted by a solid iron cuboid on sand while resting on its three different faces and to calculate the pressure exerted in the three cases.

To study and compare the pressure exerted by a solid iron cuboid on sand, we need to find its mass and weight.

The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. The usual symbol for mass is 'm' and its SI unit is kilogram.

In everyday usage, mass is often referred to as weight, the units of which are often taken to be kilograms. In scientific use, weight is the gravitational force acting on a given body, while mass is an intrinsic property of this body.

On the surface of the Earth, the weight W of an object is related to its mass m by W = m.

Having defined Mass, what about the Weight of an object?

In science, the weight of an object is the force on the object due to gravity. Its magnitude (a scalar quantity), often denoted by W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g. Thus, W = mg. Since the weight is a force, its SI unit is Newton.

Simply stated, weight is the force acting vertically downward. The weight of an object is the force with which it is attracted towards the earth, that is:

F = m x g

For an object in free fall, when gravity is the only force acting on it, the expression for weight follows Newton's Second Law.

W = F, thus:

W = m x g

Here ‘g’ is the Earth's gravitational field strength, equal to about 9.81 m s−2.

An object's weight depends on its environment, while its mass does not. The SI unit of weight is the same as that of force, that is, Newton (N).The force acting on an object perpendicular to the surface is called thrust. The effect of thrust depends on the area on which it acts. Thus:

Thrust = F = m x g

The thrust on unit area is called pressure. Thus:

Pressure = Thrust / Area

SI unit of pressure is N/m2 or Nm-2 (Newton per square metre).

In honour of scientist Blaise Pascal, the SI unit of pressure is called pascal, denoted by Pa.

Fill ¾ ths of a tray with dry sand and level it.

• Measure the dimensions of a solid iron cuboid accurately using a scale. Mark the three faces of the cuboid as A, B and C.

• Place the solid iron cuboid by the surface A on the plane levelled sand in the tray.

• After a few minutes, remove the Iron cuboid and you will see that it has made a depression in the sand.

• Measure the depth (depression) it has made in the sand using the scale.

• Repeat the same procedure for the other two surfaces.

Gravitational force on the environment = ……..

• Area occupied by surface A in the sand = .............

• Area occupied by surface B in the sand = .............

• Area occupied by surface C in the sand = .............

• Pressure made by the surface A in the sand = ............. N

• Pressure made by the surface B in the sand = ............. N

• Pressure made by the surface C in the sand = ............. N

• Depression made by the surface A in the sand = ............. cm

• Depression made by the surface B in the sand = ............. cm

• Depression made by the surface C in the sand = ............. cm

1. Dried sand must be used.

2. The tray must have significant length and width.

3. Appropriate cuboid of dimension must be used

• Manual of Secondary Science Kit for Classes IX and X - Published by NCERT

• Science textbook for class IX – Published by National Council of Educational Research and Training, New Delhi

• Pressure exerted by Solids - Better Lesson.com

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