IGCSE Physics 0625

1.2 Motion

Objective: Know that weights (and masses) may be compared using a balance

This section focuses on understanding how mass and weight can be compared using a balance. We will explore the principles behind using a balance and the relationship between mass and weight.

Mass and Weight: Definitions

Mass is a measure of the amount of matter in an object. It is an intrinsic property of an object and remains constant regardless of location. The SI unit of mass is the kilogram (kg).

Weight is the force exerted on an object due to gravity. It depends on both the mass of the object and the acceleration due to gravity. The SI unit of weight is the Newton (N).

Comparing Mass and Weight with a Balance

A balance is an instrument used to compare the masses of two objects. There are different types of balances, but the principle remains the same: comparing the forces exerted by the objects due to gravity.

Types of Balances

1. Beam Balance: This is the most common type of balance. It consists of a beam supported by a pivot point. Two arms extend from the beam, and weights can be placed on either arm.
2. Spring Balance: This type of balance uses a spring that stretches or compresses proportionally to the weight placed on it. The reading on a scale attached to the spring indicates the weight of the object.

Using a Beam Balance to Compare Mass

To compare the masses of two objects using a beam balance:

1. Place one object on one arm of the balance.
2. Place the other object on the other arm of the balance.
3. If the two arms are level, the masses of the two objects are equal.
4. If one arm is lower than the other, the object on the lower arm is heavier (has greater mass).

The Relationship Between Mass and Weight

Mass and weight are related by the following equation:

$$ \text{Weight} = \text{Mass} \times \text{Acceleration due to gravity} $$

Where:

• Weight (W) is measured in Newtons (N).
• Mass (m) is measured in kilograms (kg).
• Acceleration due to gravity (g) is approximately 9.8 m/s² near the Earth's surface.

Table: Comparison of Mass and Weight

Property	Mass	Weight
Definition	Amount of matter in an object	Force exerted on an object due to gravity
SI Unit	Kilogram (kg)	Newton (N)
Is it intrinsic?	Yes	No (depends on gravity)
Does it change with location?	No	Yes (due to variations in gravitational field)

Conclusion

Balances provide a practical way to compare the masses of objects. Understanding the relationship between mass and weight is crucial in physics. While mass remains constant, weight can vary depending on the gravitational field.