2.1 Mass and weight
2.1.1 Mass and weight
Mass
Mass is the measure of an object’s amount of matter, unaffected by its physical state (solid, liquid, or gas).
Unit: The unit of mass is kg.
Mass indicate two primary effects:
- Resistance to Change in Motion:
- Mass resists changes in motion.
- Greater mass results in increased resistance to acceleration or deceleration.
- Gravitational Attraction:
- All objects experience gravitational attraction towards the Earth.
- Greater mass leads to a stronger gravitational pull from the Earth.
Mass is a quantitative measure of a body’s inertia, representing its ability to maintain a state of rest or motion. It is a scalar quantity, measured in kilograms (kg) as the standard unit. The relationship between kilograms and grams is expressed as 1 kg = 1000 g.
2.1.2 – Weight
Weight is the gravitational force on an object.
Unit: It is measured in newtons (N).
- Determined by Mass:
- The weight of an object is directly determined by its mass.
- Weight is the gravitational pull applied by the Earth on the object, and this force is proportional to the object’s mass.
- Relation between Mass and Weight:
- The greater the mass of an object, the greater its weight.
- Mathematical Expression:
Mathematically, weight is the product of an object’s mass and the gravitational field strength (or free fall acceleration):
Weight (W) = mass (m) × gravitational field strength (g)
Gravitational Field Strength
Gravitational field strength is the force per unit mass acting on an object in a gravitational field.
- Value on Earth:
On Earth, the gravitational field strength (g) is approximately 9.8\( \frac{m}{ s^2}\) or 9.8\( \frac{N}{ kg}\)
- Variability:
- The value of g is not constant and can vary from location to location.
- It depends on factors such as mass distribution and radius.
❓ Exam Questions
0625/0972-May-June-21-2021-Q4
An object of mass 2.0 kg is taken from the Earth, where the gravitational field strength is 10 N / kg,to the Moon, where the gravitational field strength is 1.6 N / kg.
Which row is correct?
0625/0972/21-Oct-Nov-2020-Q5
A sphere P, made of steel, has a weight of 10 N on Earth.
Another sphere Q, also made of steel, has a weight of 10 N on Mars.
The gravitational field strength on Earth is greater than the gravitational field strength on Mars.
Which statement is correct?
2.1.3- Comparison of mass and weight
- Mass:
- Constant: The mass of an object always remains constant.
- Weight:
- Variability: The weight of an object varies depending on the strength of the gravitational field at different locations.
- Example:
- On Earth: An object with a mass of 1kg has a weight of 10N because g is approximately 10\( \frac{N}{ kg}\)
- On the Moon: The weight of the same object changes since the gravitational field strength (g) on the Moon is \( \frac{1}{ 6}\) times that of Earth. Therefore, the weight becomes 1.667N.
- Comparison Tool:
- A balance can be used to compare the weights of two objects.
- Calculation
The mass (m) of an object can be calculated using the formula m =\( \frac{W}{g}\) where W is the weight and g is the gravitational field strength.
❓ Exam Question
1524/22-j21-2021-Q4
Two objects, X and Y, are suspended from identical springs. The extension in both springs is the
same.
What does this show about the masses and about the weights of objects X and Y?
0625/0972/22-Feb-Mar-2020-Q4
Diagram 1 shows a piece of flexible material that contains many pockets of air. Diagram 2 shows the same piece of flexible material after it has been compressed so that its volume decreases.
What happens to the mass and to the weight of the flexible material when it is compressed?
Definitions
- Mass: The property of an object that resists any change in motion.
- Weight: The weight of an object on the Earth is defined as the force acting on the object by the Earth’s gravity. It is equal to the product of mass of an object and gravitational field strength at its location.
- Balance: The apparatus that is used to compare different weights to demonstrate that which weight is larger.