Motion and forces Study Guide

Weight is a measure of the gravitational force exerted on an object due to its mass. Unlike mass, which is an intrinsic property of an object and remains constant, weight can change depending on the strength of the gravitational field the object is in. For example, an object would weigh less on the Moon than on Earth, even though its mass remains the same. The relationship between weight, mass, and gravitational field strength is given by the equation: Weight (N) = Mass (kg) × Gravitational Field Strength (N/kg). The gravitational field strength (g) represents the force per unit mass exerted by a gravitational field. On Earth, the average gravitational field strength is approximately 9.8 N/kg.

Weight is the force exerted on an object due to gravity. It is a vector quantity, meaning it has both magnitude and direction, always acting vertically downwards towards the centre of the Earth. To measure weight accurately, a specific type of instrument is required: a spring balance or a newtonmeter. These devices operate on the principle of Hooke's Law, where the extension of a spring is directly proportional to the force applied, within its elastic limit. When an object is suspended from a spring balance, the gravitational force acting on its mass (its weight) causes the spring to extend. A calibrated scale, typically marked in Newtons (N), indicates the magnitude of this force. It is important to distinguish weight from mass; mass is a measure of the amount of matter in an object and is measured in kilograms using a balance, while weight is a force and is measured in Newtons using a spring balance.