Module 4—Gravitational Force

Lesson Summary

 

In this lesson you explored the following questions:

The law of falling bodies states that objects near Earth’s surface will fall at exactly the same rate with constant acceleration. This acceleration (g) is caused by Earth’s gravitational field—a three-dimensional region of influence surrounding the planet. The field strength (g) increases as you approach the mass—Earth, in this context—and it is at a maximum at the surface (–9.81 m/s2). The field strength (g) obeys the inverse square law for a gravitational field () and extends outwards, affecting the motion of objects that encounter it. These objects include planets, moons, and artificial satellites.

 

The terms weight and mass are often confused and used incorrectly. Mass is a measure of the amount of matter that makes up an object, whereas an object’s weight is the force of gravity on the object. The magnitude of this force is equal to the product of the object’s mass and the acceleration due to gravity at its location. Weight is a measure of the force of gravity on an object. Note that weight is based on Newton's second law (), where the acceleration is due to gravity. Expressed as an equation, it is as follows:

 

 

Quantity

Symbol

SI Unit

weight

N

mass

m

kg

acceleration due to gravity

m/s2

* The acceleration due to gravity at Earth's surface
averages around –9.81 m/s2.

 

Lesson Glossary

 

gravitational field: a three-dimensional field created by any object with mass and extending outward in all directions, influencing other masses

 

gravity: a force of attraction towards the centre of a mass

 

inverse square law: any physical law stating that some quantity is inversely proportional to the square of the distance from a point

 

mass: the physical amount of matter that makes up an object