Edexcel IGCSE Physics 复习笔记 4.2.2 Gravitational Potential Energy

• The gravitational potential energy (GPE) of an object (also known as its gravitational store) is defined as:

The energy an object has due to its height in a gravitational field

• This means:
  • If an object is lifted up it will gain GPE
  • If it falls, it will lose GPE

   

• The GPE of an object can be calculated using the equation:

GPE = mgh

• Where:
  • GPE = gravitational potential energy, in Joules (J)
  • m = mass, in kilograms (kg)
  • g = gravitational field strength in Newtons per kilogram (N/kg)
  • h = height in metres (m)

   

The mass now has GPE as it is lifted above the ground

Gravitational Field Strength

• The gravitational field strength (g) on the Earth is approximately 10 N/kg
• The gravitational field strength on the surface of the Moon is less than on the Earth
  • This means it would be easier to lift a mass on the Moon than on the Earth

   

• The gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) is more than on the Earth
  • This means it would be harder to lift a mass on the gas giants than on the Earth

   

Some values for g on the different objects in the Solar System

• The two graphs below show how GPE changes with height for a ball being thrown up in the air and when falling down

Graphs showing the linear relationship between GPE and height

Step 1: List the known quantities

• • Mass of the man, m = 70 kg
  • Gravitational field strength, g = 10 N/kg
  • Height, h = 3 m

   

Step 2: Write down the equation for gravitational potential energy

GPE = mgh

Step 3: Calculate the gravitational potential energy

GPE = 70 × 10 × 3 = 2100 J