Question

Which of these statements is scientifically correct? "The mass of the student is \(56 \mathrm{~kg}\)." "The weight of the student is \(56 \mathrm{~kg}\)."

Short answer

The statement 'The mass of the student is 56 kg' is scientifically correct while the statement 'The weight of the student is 56 kg' is not.

Step-by-step solution

Evaluate the statements

First, let's take a look at the two statements one by one. The mass of an object is the amount of matter it contains and is measured in kilograms (kg). Accordingly, saying 'The mass of the student is 56 kg' is scientifically correct.

Verify the units

Moving on to the second statement 'The weight of the student is 56 kg', it immediately appears scientifically incorrect. The reason is that weight is the force exerted by the gravity on an object and the unit of force is not kilograms (kg), but newtons (N). Weight is obtained by the product of mass and acceleration due to gravity, which in this case should render a unit of newtons (N), not kilograms (kg).

Key concepts

Understanding Mass

Mass is a fundamental property of matter. It describes the quantity of matter in an object, regardless of its location in the universe. Mass does not change just because an object moves to a different place.
For instance, a student's mass on Earth will be the same as their mass on the Moon. Mass is measured in kilograms (kg), which is the SI (International System of Units) unit for mass.
To further understand mass:

• It is independent of gravity. Even in space where there is almost no gravity, an object's mass remains the same.
• It is a scalar quantity, which means it only has magnitude and no direction.
• Mass can be thought of as a measure of an object's resistance to acceleration when a force is applied.

Understanding these points can help you correctly identify situations where talking about mass is more appropriate than weight.

Defining Weight

Weight is slightly more complicated than mass because it involves gravity. Weight is the force of gravity acting on an object's mass.
This means that if you are on a different planet where the force of gravity differs from Earth's, your weight would change, although your mass would remain the same.
Weight is measured in newtons (N), the SI unit for force.

• Weight is a vector quantity, which means it has both magnitude and direction. The direction is always towards the center of the gravity source, like the center of the Earth.
• The formula for calculating weight is: \( W = m \times g \), where \( W \) is weight, \( m \) is mass, and \( g \) is the acceleration due to gravity.
• Commonly, the standard acceleration due to gravity on the Earth's surface is approximately \( 9.81 \, \text{m/s}^2 \).

Understanding weight can prevent common mix-ups between mass and weight.

The Role of Units of Measurement

Units of measurement are crucial for accurately conveying scientific information. They provide a standard way of expressing physical quantities.
In terms of mass and weight, it is important to use the correct units to avoid confusion.

• Mass is measured in kilograms (kg). This is a base unit of the International System of Units (SI), representing the quantity of matter.
• Weight, being a force, is measured in newtons (N). This reflects its definition as a force due to gravity.
• Misusing units leads to inaccuracies, such as mistakenly using kilograms to denote weight, instead of newtons.

Being meticulous about units ensures clear and precise scientific communication, and helps eliminate common misunderstandings involving mass and weight.