Edexcel IGCSE Physics 复习笔记 1.2.5 Weight

• Weight is defined as:

The force acting on an object due to gravitational attraction

• Planets have strong gravitational fields
  • Hence, they attract nearby masses with a strong gravitational force

   

• Because of weight:
  • Objects stay firmly on the ground
  • Objects will always fall to the ground
  • Satellites are kept in orbit

   

Some of the phenomena associated with gravitational attraction and the weight force

• Weight, mass and gravitational field strength are related using the equation:

• This can also be written as:

W = m × g

• g is known as the acceleration due to gravity or the gravitational field strength
  • On Earth, this is equal to 9.81 m/s² (or N/kg)

   

• The weight that an object experiences depends on:
  • The object's mass
  • The mass of the planet attracting it

   

• Mass (measured in kilograms, kg) is related to the amount of matter in an object
• Weight (measured in newtons, N) is the force of gravity on a mass
  • The weight of an object and the mass of an object are directly proportional
  • The size of this force depends on the gravitational field strength (often called gravity, g, for short)

   

Step 1: State the equation linking weight and mass

• • The equation linking weight and mass is:

   

W = m × g

Step 2: List the known values

• • The question instructs us to take the Earth's gravitational field strength as 10 N/kg
  • The question also instructs us to take the Moon's gravitational field strength as 2 N/kg
  • Mass, m = 40 kg

   

Step 3: Calculate Isabelle's weight on Earth

• • Substituting the values of mass and Earth's gravitational field strength into the equation gives:

   

W = 40 × 10 = 400 N

Step 4: Calculate Isabelle's weight on the Moon

• • Substituting the values of mass and the Moon's gravitational field strength into the equation gives:

   

W = 40 × 2 = 80 N

Step 5: Comment on the two values of weight

• • Isabelle's weight is greater on Earth than on the Moon
  • This is because the Earth has a larger gravitational field strength than the Moon, so Isabelle's weight force (the force of gravity pulling down on her) is larger on Earth than on the Moon