Mass, Weight & Gravitational Field Strength (Edexcel IAL Physics)

Spec point — 10

Mass, Weight & Gravitational Field Strength

Mass

• Mass is the measure of the amount of matter in an object

  • Consequently, this is the property of an object that resists change in motion

• The greater the mass of a body, the smaller the change produced by an applied force

  • The SI unit for mass is the kilogram (kg)

Weight

• Weight is the force a body experiences due to being in a gravitational field, it is given by the equation

W = mg

• Where

  • m = mass (kg)
  • g = gravitational field strength (N kg⁻¹)

Gravitational Field Strength

• Gravitational field strength is the force per kilogram that acts on an object, it is found using the equation

g = $\frac{F}{m}$

• Where

  • F = weight (N)
  • m = mass (kg)

• On the Earth's surface the average gravitational field strength =9.81 N kg⁻¹

Constant Acceleration in Freefall

• Freefall is used to describe falling objects where the only force is weight

  • Drag forces are ignored
  • By considering freefall we can see that all objects must fall with exactly the same value for acceleration, regardless of their mass or weight