How Does Force Affect Motion?

Gerald Darling
Type Category
Instructional Materials
Article , Lesson/Lesson Plan , Activity
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be "fully aligned," the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.



This article describes a series of easy to implement activities that develop the student’s ability to explain what force is, how forces can change the motion of an object, and identify forces acting on an object at rest.  It will also enable students to describe what friction is using everyday examples.  Although these activities were conducted with a class of fourth grade students, they easily adapted for implementation with third graders.

Intended Audience

Educational Level
  • Grade 3
  • Grade 4
  • Upper Elementary
Access Restrictions

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Performance Expectations

3-PS2-1 Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.

Clarification Statement: Examples could include an unbalanced force on one side of a ball can make it start moving; and, balanced forces pushing on a box from both sides will not produce any motion at all.

Assessment Boundary: Assessment is limited to one variable at a time: number, size, or direction of forces. Assessment does not include quantitative force size, only qualitative and relative. Assessment is limited to gravity being addressed as a force that pulls objects down.

This resource appears to be designed to build towards this performance expectation, though the resource developer has not explicitly stated so.

Comments about Including the Performance Expectation
This article details the series of simple investigative activities with students tossing and kicking different sizes of balls to learn that a force is a push or pull that has strength and can cause an object to move, stop, and change speed or direction. The student’s understanding of an object at rest is then addressed with the teacher engaging the students in the simple act of dropping a book on their desk and asking, “Gravity is pulling the book down, but what does the desk do?” Through the application of what they learned about forces, students recognize the desk is applying a force, pushing it up. When asked to respond in writing to the following question, “What happens to gravity when a book is sitting on the desk?”, the typical student response was: “Gravity is balanced by the desk pushing up.” To more explicitly address this performance expectation, it is recommended that the gravity investigation be made more open-ended by dropping the book and asking, “What force(s) are acting on the book?” The concept of balanced and unbalanced forces needs be made explicit as they discuss their observations. To reinforce student understanding, the teacher could also place a flat object (such as a book) on a triangular prism and discuss what forces are at work when the flat object is level vs. tilted. Students could then be asked to plan their own investigation to provide evidence the effects of balanced and unbalanced forces on the motion of an object. It is then recommended that the teacher have their students revisit and apply their understanding of balanced and unbalanced forces to their initial investigations with the ball.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
Through engagement in hands-on activities, the students observe that the application of force by tossing the ball caused it to move, that the more forceful the toss, the greater the speed in which the ball moved, that catching the ball produced an oppositional force causing the ball to stop, and that kicking the ball as they do in soccer changed its direction. The students then used their observations to explain phenomena as they investigated the forces of friction and gravity on the motion of objects. Throughout the activities students are asked questions to explain the phenomena observed. Students will also have lots of questions of their own as they observe the effects of forces on motion. These questions should be recorded as they are the basis for planning and conducting investigations by the students themselves.

Disciplinary Core Ideas

This resource appears to be designed to build towards this disciplinary core idea, though the resource developer has not explicitly stated so.

Comments about Including the Disciplinary Core Idea
Tossing the ball enabled students to recognize that the ball is at rest until the force of the toss causes the ball to move. Rolling the ball on different surfaces enabled students to learn that friction is an oppositional force that stops the ball. Dropping the book on the desk enabled students to recognize that the book was at rest because the downward pull of gravity was balanced by the upward push of the table. Further questioning and discussion is recommended to make the connection between what was learned through these activities with the concepts that a zero net force is the result of multiple forces acting on an object, and that forces that do not add up to zero causes changes in an object’s motion.

Crosscutting Concepts

This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.

Comments about Including the Crosscutting Concept
It is recommended that students explicitly identify a cause and an effect when describing each of the force and motion relationships they have discovered. Once they have done so, students should also be asked to reflect on how they were able to determine this cause and effect relationship.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The lessons presented in this article provide grade-appropriate elements of the Practices, Disciplinary Core Ideas and Crosscutting Concepts that enable students to make sense of how forces affect motion. Students are given many opportunities to make observations and produce data that serve as the basis for evidence to explain the phenomena. To more rigorously align these lessons to the dimensions of the NGSS, it is recommended that the concept of balanced and unbalanced forces be more explicitly applied as they conduct their investigations. It is also recommended that the students explicitly identify a cause and an effect when describing the force and motion relationships they have discovered.

  • Instructional Supports: These lessons provide students with first hand experiences that enable them to make sense of phenomena of forces and motion. It provides opportunities for students to connect their explanation of phenomena to their own experiences. It also provided opportunities for students to express, interpret, and represent their ideas to support their learning. The lessons are structured to address student misconceptions about the effect of forces on the motion of objects, addressing their conceptual needs. It is suggested that students be allowed to diagram their thinking in the pre-assessment, which provides a writing alternative for students that are struggling in this area. It is recommended that this alternative be provided for all the formative assessment questions that were required of the students as they engaged in the investigative activities. Independent investigations are recommended for high performing students to extend their learning.

  • Monitoring Student Progress: A pre-assessment survey is administered to assess student’s understanding of how forces can change the motion of an object (disciplinary core idea and crosscutting concept). After each investigative activity, students are asked to respond to a question, which provided formative assessment information. It is recommended that the pre-assessment survey be administered at the end of these lessons to summatively assess student learning. Students could also be asked to identify examples of how forces affect the motion of objects in their everyday lives to provide a more accessible/unbiased way to assess the students.

  • Quality of Technological Interactivity: This resource does not include a technologically interactive component.