N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
FORCE AND MOTION
Throughout childhood, students have learned that things drop, roll, float, sink,
slide, and balance. This is because we live in a world of constant motion where
forces are in action all around us, resulting in matter constantly being pushed and
pulled in different directions. Elementary students learn that a force is a push or
a pull on an object, and explore this concept conceptually, often relating to forces
in nature. It is in 6th grade that students begin a more quantitative analysis
regarding how force affects motion. By measuring and graphically representing
these concepts, students build a foundation for further understanding in the
discipline of physics.
Defining Force and Motion
Forces can affect objects in several ways. For example, forces acting on an object
at rest can set the object in motion. They can also change a moving object’s speed
and/or direction. A force can also affect an object without making it move, such
as changing its shape or weight. The 6th grade student should be introduced to
inertia as they strive to understand this relationship between force and motion.
Inertia is an object’s tendency to resist a change in motion. The concept of inertia
is also referred to as Newton’s First Law of Motion. Sixth grade students should
not be required to memorize and differentiate between Newton’s Laws of Motion
as they will be identified in later grades.
Students should learn that all objects have inertia and that the greater the
object’s mass, the greater its inertia and the larger the force needed to overcome
this inertia. For example, when a student pushes a box, the box will move in the
direction of the force and will continue to move as long as the force is applied. The
greater the force, the greater the distance the box will move. The greater the
mass of the box, the greater the force needed to cause a change in its position.
Students should be exposed to everyday examples of inertia. The following are
examples in which this law is illustrated:
 Brakes are slammed in a car, and the passengers body continues to move
forward in the original direction of the car
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science

Unit 2
Force and Motion
Spring 2006
A table cloth is quickly pulled out from under dishes, and they stay in place
Objects that come in contact with each other exert a force on each other. For
example, when a book is placed on a table, the book exerts a force on the table and
the table exerts a force on the book. In addition, every force has a certain strength,
or magnitude, and a direction. A rock on the ground exerts a force on the ground equal
to its weight in a downward direction. Forces can affect objects in several ways.
They can set a stationary object in motion, they can change an object’s speed or
direction, and can even change an object’s shape.
Motion is the change in position of an object. Changing position and recognizing motion
is not as easy as it sounds. Motion is relative. Reference points are needed to
describe the motion. The location of an object is how far the object is located from
the reference point (also known as the position of the object). Some familiar
reference points include north, south, east, west, up, and down.
Forces that Affect Motion
Sixth grade students need to begin to develop an understanding of gravity as a force
of attraction between objects that have mass. Since all matter has mass, students
should understand that gravity acts as a force between all objects. The strength of
the gravity between two objects depends on the mass of the objects and the distance
between them. This concept should also be explored when students learn about the
components of our solar system later in the year. When using the term mass of an
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
object, it is always a good idea to check for misconceptions. Make sure students are
not confusing mass with weight. Mass is a property of an object and does not depend
on an object’s location. Weight is a measure of the force of gravity acting on an
object. It can vary depending on the object’s location. Students should be reminded
that their body would have the same mass whether they were on Earth or on the
moon. The body’s weight on the moon would be less because the moon’s gravity is less
than Earth’s gravity since the moon is smaller than Earth.
Other forces that affect motion include magnetism and electricity. Students can
discover how these forces affect motion by exploring with magnets and with static
electricity. Both magnetism and electricity are caused by positive and negative
charges in matter. Simple experimentation with magnets and small magnetic objects
such as paper clips demonstrate the push and pull of magnetism. Rubbing a balloon
with a piece of wool and watching its effect on another balloon and other items also
demonstrates the push and pull force of electricity in a safe way. They should
determine that like gravity, magnetic and electric forces decrease with distance.
Students should have the opportunity to experiment with friction. Friction is a force
that opposes the motion between two surfaces that are in contact with each other.
Friction might prevent motion from starting or it might oppose motion in progress.
There are different types of friction, classified as sliding, rolling and fluid friction.
Students should be exposed to examples of each type, but they do not need to learn
these terms or classify according to type. It is more important that they have a
conceptual understanding that friction can occur in many different ways or situations.
This should also include an understanding that friction does not have to occur between
two solid objects, but can occur as objects move through liquids and gases as well.
Students sometimes view friction as a negative or undesirable force that opposes
motion. As a result, it is important for students to understand that friction can be
very helpful, such as when brakes are applied to stop a car. Students should be able
to recognize examples of friction in everyday life. The following are some examples:
 a book sliding across a desk
 a car’s wheels rolling on the ground
 an airplane moving through the air
 a swimmer moving through a pool of water
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
Describing Motion
Motion can be described in many ways. How fast did an object go? How far did an
object go? Where did the object go? Did the object slow down or speed up? Did it
turn to the left or right? Speed is the distance traveled by an object in a given
amount of time (s = d /t). Velocity is described as the speed of an object in a given
direction. An example would be a plane traveling 600 km/hr in a westward direction.
Acceleration is any change in speed or direction (velocity) over time. Students should
practice calculating speed, velocity and acceleration. The formula for speed appears
on the TAKS formula chart, indicating it can be tested. Acceleration appears on the
formula chart as part of the formula for force, a calculation that will be performed in
7th grade. Calculating acceleration by itself builds the foundation for understanding
the equation for calculating force next year. It should also be noted that students do
not need to be able to manipulate formulas to solve for other variables. For example,
the 6th grade student needs to be able to use the formula s= d /t to solve for speed
but not to solve for distance or time. The following formulas should be utilized in this
unit:



speed = distance / time
velocity = distance / time (in a particular direction)
acceleration = (final velocity – starting velocity) / time it takes to change velocity
Force is measured in units called Newtons (N) and should be measured with a spring
scale. At any given time, more than one force acts on an object. Forces might be
applied in the same direction, such as when two people work together to move an
object. Forces might be applied to work against each other, such as in tug-o-war. The
net force on an object is the combination of all of the forces acting on it. When the
net force on an object is zero, the forces are balanced and there is no change in
motion. When the net force on an object is greater than zero, the forces are said to
be unbalanced. Unbalanced forces produce a change in the motion of an object.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
Students should practice finding the net force in various situations. Forces can be
represented by arrows as shown in the illustrations below. Arrows show direction.
The length of an arrow and/or numbers that accompany the arrows show
magnitude. The width of an arrow should not be used to indicate the magnitude of
a force.
When the forces are acting together, students will simply add them together.
+
=
net force
Two forces combine to produce a
larger force. This is called having
an overall “net force”.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
When forces are moving in opposite directions, students will subtract the smaller
force from the larger one to find the net force.
+
=
net force
Two forces subtract from each
other, and it causes movement in
the direction of the larger force.
Two equal forces pushing against one another in opposite directions will cancel each
other out and no movement will occur.
net force
+
=
0
Balanced forces = net force of zero
Note: These skaters are in a state of equilibrium, and movement is not occurring.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
6
N o r th E a s t In d e pen d e nt S c ho o l Di s tr ic t
6th Grade Science
Unit 2
Force and Motion
Spring 2006
Changes in motion can be represented on a graph. Students should have practice in
constructing and interpreting graphs that represent changes in motion. A distancetime graph can be used to represent an object’s movement. Time is measured on the x
axis (horizontal axis) and distance is measured on the y axis (vertical axis). Units for
time and distance should be in metric units, such as seconds, minutes, meters,
centimeters, etc. On this type of graph, the steepness of the slope of the line is
directly proportional to the speed of an object. Horizontal lines represent a stop in
motion. Examples of such graphs are as follows:
Graph representing constant speed
Distance
in meters
0
1
2
3
4
5 6 7 8 9
Time in seconds
10
11
12
Graph representing constant speed
followed by a stop
Distance
in meters
0
1
2
3
4
5 6 7 8 9
Time in seconds
10
11
12
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional design. They are
not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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