# Vocabulary - Gravity And Orbits

Name
Date
Vocabulary
STUDENT RESOURCE 3.1
INFORMATION SHEET
acceleration a change in an object’s
gravity the force of attraction that exists
speed or direction
between all objects
Acceleration happens when an object’s
The strength of gravity, also called
speed changes or when its direction
gravitational force, depends on the
changes. On Earth, a falling object
distance between the objects and the
accelerates 9.8 meters per second, per
masses of the objects. Gravity is stronger
second (9.8 m/s
2
). This means that every
between objects that are closer together
falling object, regardless of its mass,
than between objects that are farther
falls at a speed of 9.8 m/s during the
apart. Objects with more mass exert a
ﬁrst second, 19.6 m/s during the second
stronger gravitational force than objects
second, 28.4 m/s during the third second,
with less mass.
and so on. This rate of acceleration is the
weight the measure of the force of
same for all objects, ignoring air friction.
gravity on an object
friction the force between two surfaces
Different planets and moons exert
rubbing against each other, or between
different gravitational forces on objects
a surface and a ﬂuid, such as air
at their surface. For example, the Moon’s
Friction between air and a falling
gravitational force on an object is only
object slows the rate of fall of the
about one-sixth that of Earth’s. On the
object—particularly on objects that have
Moon, you would weigh only one-sixth
a large surface area compared to their
as much as you weigh on Earth.
mass. The Moon has no air, so friction
does not slow the rate of fall. A feather
and hammer would fall at the same rate
on the Moon.
EXPLORING SPACE • SECTION 3 GRAVITY AND ORBITS