N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
FORCE & MOTION
The Relationship Between Force and Motion
The 7th grade student should come with an understanding of a force as a push or a
pull, a concept first learned in 3rd grade. The 6th grade student described the
changes in position of motion and speed that occur when acted upon by a force, and
demonstrated that motion can be measured and represented graphically. The 7th
grade student will focus on understanding the relationship between force and
motion including the concepts of balanced and unbalanced forces, Newton’s First
Law of Motion, and a study of potential versus kinetic energy.
A force is a push or pull on matter. Forces are the cause of motion. Forces have
magnitude (size) and direction. The direction of the force is important. An object
that is not subjected to a force will move at a constant speed and in a straight line.
Some forces reinforce or cancel each other out. Forces that are different in size
and direction will cause changes in the speed or direction of an object’s motion. A
common unit used to measure force is known as the Newton (N). Friction is a force
that slows down motion. Larger forces create more friction.
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. The 7th grade student should be able to calculate the net
force in simple models or problems.
+
=
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 t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
net force
+
=
Two forces subtract from each
other, and it causes movement in
the direction of the larger force.
net force
+
=
0
Balanced forces = net force of zero
When the net force an object is greater than zero, the forces are said to be
unbalanced. Unbalanced forces can cause an object to start to move, to stop
moving or even change directions. When two forces are acting in the same
direction, they add together to become a larger force. If one force acting on an
object is larger than the other force acting on the object in the opposite
direction, the forces are subtracted and it is said that there is a net force in the
direction of the greater force. Two equal forces pushing against one another in
opposite directions will cancel each other out and no movement will occur. Since 7th
grade teachers address systems in equilibrium with students, this would be an ideal
time to introduce students to what equilibrium means. When net forces equal zero,
or there is no movement in a system, a state of equilibrium has been reached. This
concept will reappear in earth systems when addressing catastrophic events, in
ecology when studying succession, and in human body systems when addressing
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.
2
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
homeostasis. It should be noted that 7th grade is the first time students will
address systems as being in equilibrium or not.
These skaters are in a state of equilibrium, and movement is not occurring.
Motion is described as the state in which one object’s distance from a point of
reference is changing. Some motions are simple and some are complex. When a
student leaves school at the end of the day, there is motion all around. For example
the student might notice that birds are flying, clouds are moving, the wind is
blowing, and a car goes by. When a student is sitting perfectly still, there is still
motion occurring. The student is breathing and blood is circulating throughout the
body. Since motion is relative, reference points are needed to describe the
motion. The location of an object is how far the object is from the reference
point (also known as the position of the object), and as an object moves, its
location to a reference point is changing also. One way to show that an object has
moved is to use a distance-time graph. Students first represented motion
graphically in 6th grade (TEKS 6.6B).
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 t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
Newton’s First Law of Motion
Newton’s First Law states that an object in motion tends to stay in motion and an
object at rest will stay at rest unless acted upon by an unbalanced force. In
discussing Newton’s First Law, students should understand it is also called the Law
of Inertia. Inertia is the tendency of an object to resist any change in motion.
This law explains why people riding in cars need to wear seat belts. A moving car
has inertia and so do the people riding in it. If the driver suddenly applies the
brakes, the riders continue moving forward at the speed the car was going, unless
the rider is wearing a seat belt. The seat belt applies the unbalanced force to
prevent the rider from going forward. In another example, if an object is tossed
from a space station located in the vacuum of outer space, it will move forever by
virtue of its own inertia because there is no outside unbalanced force to stop it.
Newton’s First Law of Motion also describes how the net forces acting on an object
is zero if the object is at rest or not moving. Equal forces acting on an object in
opposite directions are called balanced forces. A diver standing on a diving
platform is affected by different forces. Gravity pulls the diver down towards the
pool, but the diving platform pushes him up. These two forces balance each other
and as a result, the diver stays put on the platform. If the diver steps off the end
of the platform, however, the force of the platform no longer balances the force
of gravity. The unbalanced force causes the diver to accelerate into the 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 t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
Forces in Living Things
The 7th grade student is expected to relate forces to basic processes in living
organisms, including the flow of blood and the emergence of seedlings. Although
students will study human body systems in more detail in a separate unit, this is a
good time to introduce processes in living systems relating to forces and motion.
The heart supplies the force that causes blood to flow through blood vessels. The
heart, however, is only one example of a body part in which forces are at work to
carry on life processes. Other examples include the following:



The teeth apply force in breaking food into smaller pieces
Muscles in the esophagus exert a force in pushing food down the digestive
tract through peristalsis
Muscles contract and relax, creating a enough force to move bones to walk,
run, jump or engage in other life processes
Seeds sprout because the force of water pressure (also called turgor pressure)
inflates the emerging shoot. The force of the shoot straightening pulls the seed
leaves above ground.
Students should demonstrate or model the concept of forces at work in a living
organism. A small pump, plastic tubing and colored water can be utilized to show
blood flow. Students could also germinate seeds, making observations and drawing
conclusions as the process occurs.
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 t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
Potential and Kinetic Energy
Usually when a student thinks of energy, the student thinks about action or some
kind of movement. Kinetic energy is the energy of motion. The more mass an
object has, the more kinetic energy it can produce. Stored energy due to position
is called potential energy. The 7th grade student needs to illustrate examples of
potential and kinetic energy in everyday life. An example of both types of energy
is a stretched rubber band. While the band is stretched, it has potential energy.
When the rubber band is released and it flies across a room, it has kinetic energy.
An apple has potential energy in the form of chemical energy. Once eaten, the
body converts it into kinetic energy. A ball at the top of a hill has potential
energy. The ball rolling down the hill has kinetic energy. Roller coasters operate
through a series of conversions from potential to kinetic energy and back again:
The 7th grade student should also relate the concepts of potential and kinetic
energy to earth science, such as through study of geologic faults and the
movement of water. An example is when rock along a fault, a break in the earth’s
crust, is locked into place or at rest. At this time there no movement is taking
place and the fault has potential energy. If rock on either side of the fault
suddenly shifts, potential energy is released and changed into kinetic energy. This
kinetic energy produced by movement along a fault causes earthquakes, tremors,
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 t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
tsunamis, landslides and other natural disasters. Another example of this kind of
relationship can be found in a water fall. Water at the top of the fall has potential
energy, but once water moves down the fall, it has kinetic energy.
The 7th grade student should relate the concept of inertia to the amount of kinetic
energy an object has. This connects Newton’s Second Law to Newton’s First Law.
Students in 7th grade should have this conceptual understanding, but not be
required to perform calculations according to the Second Law or have to
distinguish between the two laws. This is done at the 8th grade level. An object
with a small mass has less inertia than an object with a large mass. A object with
less speed also has less inertia than an object moving with a greater speed.
Students should understand these two factors, mass and speed, influence the
amount of kinetic energy in a moving object. Objects with more mass and/or
greater speed have more kinetic energy. If a baseball and a softball are pitched at
the same speed, the softball will have more kinetic energy because it has more
mass. A fast pitch softball has more kinetic energy than a slow pitch softball.
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.
7
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
7th Grade Science
Unit 1
Force and Motion
Spring 2006
The slow pitch ball has less kinetic energy.
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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