Unit 1: Forces and Motion

Instructional Resources

OAS-S: PH.PS2.1, PH.PS2.2, PH.PS2.3, and PH.PS2.4*

Bundled Standards Analysis: Forces and Motion

*Note: Focus is on Newton's Law of Gravitation and gravitational forces. Coulomb's Law and electrostatic forces are addressed in the "Fundamental Forces, Electricity and Magnetism" bundle.

Driving Question

• How can we make athletic helmets more effective at preventing harm?

Essential Questions

• How can an object's continued motion or changes in motion be predicted?

• How can mathematical models be used to describe the conservation of momentum during interactions within a system?

• How can an object be modified to minimize the average force it experiences during a collision?

• How can Newton’s Law of Gravitation be used to predict gravitational forces between objects?

Examples of Student-Developed Initial Questions

• What is a force?

• How do I determine what is and what is not part of a system?

• How are force and momentum similar/different?

• Is my weight always the same?

• Does gravity exist everywhere?

Prior Knowledge

Each dimension in the Oklahoma Academic Standards for Science grows in complexity and sophistication across the grades. To learn more about the prior knowledge and skills students have developed in previous grades associated with the standards in this bundle, check out the links below.

Science and Engineering Practices 

Disciplinary Core Ideas 

Crosscutting Concepts 

Science and engineering practices (SEP) in Physics in K-8 build on K-8 experiences. This bundle of standards engages students with the following SEPs: 

• Analyzing and Interpreting Data

• Using Mathematics and Computational Thinking

• Designing Solutions

Disciplinary core ideas (DCI) in Physics build on K-8 experiences. This bundle of standards explores the following areas:

• Forces and Motion

• Types of Interactions

• Defining and Delimiting Engineering Problems

Crosscutting concepts (CCC) in Physics build on K-8 experiences. This bundle of standards leverages the following ways of thinking about science ideas: 

• Cause and Effect

• Systems and System Models

• Patterns

Launch Task: Phenomena Ideas

Phenomena are observable events that occur in the universe and that we can use our science knowledge to explain or predict. Engineering involves designing solutions to problems that arise from phenomena and using explanations of phenomena to design solutions. Instructional sequences are more coherent when students investigate phenomena or design problems by engaging in science and engineering practices. Read this STEM Teaching Tool Brief #28 to learn more about the characteristics of a good phenomenon or design problem for anchoring student learning.

Each phenomenon below includes teacher information resources (e.g., information about the phenomenon, data resources, videos, simulations, etc.). Due to the length or accessibility of the content, teachers should screen the resources and pull sections, photos, quotes, and data that are appropriate for Physics students to ask questions, investigate, analyze, describe, evaluate, etc.

Phenomenon: Pushing an empty shopping cart will cause it to move more than when the same push is applied to a full shopping cart. 

The net force on an object causes acceleration. While a single force acting on an object may be easy to understand, most interactions involve multiple forces and are more difficult to visualize. Educators can have their students use a force simulator, like the Forces and Motion: Basics simulator from PHET Interactive Simulations, to gather quantitative data about all the forces on an individual object. Students can use the data from the simulation to create a model that illustrates the net effect on the object's acceleration. Simulations can also be used to investigate the effects of mass on an object’s acceleration.

Phenomenon: Helmets are designed to protect a person’s head during a collision.

Momentum can be transferred between objects in a system and it is conserved in all collisions. Momentum is a part of many sports and impacts the design of helmets. The video Science of NFL Football (stop at 2:27) can be used to introduce momentum. Educators can provide further explorations that lead to an understanding of the “Conservation of Momentum”. “The NFL Helmet Challenge” is an innovation challenge that aims to encourage experts to develop a helmet for NFL players that is more protective than the currently used helmets. Educators can present information about the Safety of Football Players to help students understand how injuries (collisions) occur during a football game. Students can also use the video “Meet the Awardees” to help them develop their own ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision. 

Phenomenon: Saturn’s orbit around the Sun is a smooth path, except for when Jupiter’s orbit gets close to Saturn. 

All objects attract each other with a force of gravitational attraction. Newton’s Law of Universal Gravitation mathematically describes and predicts the effects of gravitational forces between distant objects. Students can use a simulation (e.g., Gravity Force lab) to investigate the relationships between object masses, force, and the distance between those masses. Most gravitational forces are too minimal to be noticed, and tend to only be recognizable as the masses of objects become large. Knowing all objects exert gravitational forces on each other, the small deviations in a planet’s elliptical motion can be easily explained.

Engagement Strategies 

• Educators can leverage the Student Actions and Teacher Actions found in the Forces and Motion bundled standards analysis for specific ways of engaging students with these science ideas.

• This example of a secondary science cycle of learning can support educators in developing coherent sequences of learning. 

• Modeling Phenomena can be used to illustrate phenomena students observe, helping them visually reason about what they are learning.  More strategies that support students with figuring out science ideas can be found within the Science Engagement Strategies section of the Framework. 

What It Looks Like in the Classroom

In science and engineering, evidence-based effective instruction focuses on students engaging in science and engineering investigations and design to explain phenomena or develop solutions to a problem. This section reflects a science cycle of learning that supports implementing the identified standards within this unit.

"What It Looks Like in the Classroom" is broken into Narrative Parts, written around the different Essential Questions listed at the top. Each Narrative Part includes examples for how to integrate the science and engineering practices, disciplinary core ideas, and crosscutting concepts for each standard, and includes examples of evidence teachers can gather from students that provides information about what they do and do not understand.

Narrative Part 1 of 2

Essential Question: How can an object's continued motion or changes in its motion be predicted? How can Newton’s Law of Gravitation be used to predict gravitational forces between objects?

OAS-S: 

PH.PS2.1 Analyze and interpret data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.

PH.PS2.4 Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.

(Note: Only Newton’s Law of Gravitation and gravitational forces are addressed in this bundle. Coulomb’s law and electrostatic forces are addressed in the "Fundamental Forces, Electricity & Magnetism" bundle.)

 3-Dimensional Narrative

Evidence of Understanding 

Provide students opportunities to gather observational data or information that will allow them to begin answering their questions and explain causes for the phenomena.

Educators present students with a phenomenon that represents Newton’s second law of motion (e.g., pushing an empty shopping cart vs. a full cart). Students can begin sharing their observations, wonderings, and initial ideas about what’s causing those observations to occur (e.g., how do forces affect an object's motion). Educators can use a Driving Question Board to organize student’s initial questions about the phenomenon, then provide students opportunities to gather data and information via investigations (e.g., simulations, labs, graphs, texts) related to their questions. Data and information gathered by students could include an object's mass, its position or velocity over time (via tables, graphs, or motion diagrams), relative force of interaction between the object (e.g., harder or softer pushes/pulls), and identifying other parts of the system involved (e.g., air, gravity). Students can begin analyzing and interpreting the data, looking for patterns that could explain the causes of their observations (the forces affecting an object's motion). 

To assist students with analyzing their data, educators can introduce the kinematics concepts of position, velocity, and acceleration. This can include how to interpret position vs time and velocity vs time tables and graphs to determine an object’s acceleration. Educator’s can also introduce students to Newton’s second law of motion, F_net= ma (net force equals mass times acceleration). This relationship means that more total force applied to an object will cause a greater acceleration. Likewise if applying the same force to objects with varying mass, the more massive objects will have less acceleration and the objects with less mass will have more acceleration. Students can use the evidence gathered to make claims about the cause and effect relationships between net force, mass, and acceleration for the object(s) in the phenomenon, and compare their observations to predictions from their mathematical models.  

• Organized data reveal patterns in the effect of mass and net force on acceleration.

• Claims supported by data correctly describe how the mass of an object affects its motion.

• Data analysis accurately describes the relationship between the mass of an object, the net force, and its acceleration using a mathematical model (a = F_net/m). 

Provide students an opportunity to apply their new knowledge.

Using the same science ideas around cause and effect relationships between net force, mass, and acceleration, students can use mathematical and/or computational models to predict changes in the motion of macroscopic objects. Given the external unbalanced force acting on an object and the object’s mass, students learn to calculate the acceleration of the object. Given the mass and the acceleration of an object, students should be able to calculate the net force acting on the object. Students can analyze simple free-body diagrams to calculate the net forces on known masses, and, subsequently, determine that object's acceleration (motion). Students can carry out investigations using physical items or simulations to verify if their predictions were correct.

• Predictions of force correctly use mathematical models to describe proportional relationships between net force, mass, and acceleration.  

Introduce a new phenomenon to explain using patterns from student observations.

Not all forces are caused by contact. There are forces, like gravity, that act over a distance. Gravitational forces are considered a pull force, because interacting objects are pulled toward one another. Newton’s Law of Universal Gravitation can be used by students as a mathematical model to construct explanations about the effects of gravitational forces between distant objects. Newton’s Law of Universal Gravitation states that objects attract other objects with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them Fg=G((m₁m₂)/r²).

Students can begin investigating gravity using computer simulations (e.g., gravity force lab) as actual changes in the force of gravity are very difficult to observe through hands-on experimentation. In many simulations, students develop and use models to explore the relationships among the objects in the system. For example, students can plan and conduct investigations in which they manipulate the masses of interacting objects and observe changes in the force of attraction.

Students can gather evidence about factors that affect the gravitational force (e.g., mass, distance). Specifically, educators can guide students to look for patterns in the change of gravitational force related to changing mass and distance between pairs of objects (e.g., when mass increases, gravitational force increases or when distance between two objects increases, gravitational force between them decreases). Students can use the mathematical model of Newton’s Law of Gravitation to identify and describe the interaction between the two objects. When analyzing and interpreting the data, students should see a direct relationship between force and mass. Students can analyze the data to observe an inverse relationship, also when investigating the effects of distance on the force of attraction.

• By keeping the masses of the objects constant and varying the distance between them, students can reveal the inverse square relationship between the gravitational force and “r” (F_G = 1/r²). 

• By keeping the distance between the objects the same and varying the magnitude of one of the masses (e.g., doubling, halving, tripling one of the masses), students can expose how the gravitational force is proportional to the products of the masses (F_G=m₁m₂).

• Educators may need to provide additional guidance to help students finalize the equation for Newton’s Law of Gravitation with the proportionality constant (G = 6.67 x 10^-11 Nm²/kg²).

• Mathematical representations of Newton's Law of Universal Gravitation are used to describe how distance and mass affect gravitational force between two objects.

• Mathematical representations are used to identify the patterns in gravitational force when mass and/or distance is changed.

• Mathematical representations are used to accurately predict the gravitational force between two objects in a system.

Narrative Part 2 of 2

Essential Question: How can mathematical models be used to describe the conservation of momentum during interactions within a system? How can an object be modified to minimize the average force it experiences during a collision?

OAS-S: 

PH.PS2.2 Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.

PH.PS2.3 Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision.

3-Dimensional Narrative

Evidence of Understanding

Provide students with opportunities to investigate a phenomenon, and organize/analyze data.

Students can plan and carry out investigations (e.g., collision carts and low friction cart tracks, Collision Lab PhET simulation) to observe objects interacting during collisions. Students can use qualitative observations as evidence for supporting conservation of momentum (e.g., observing that equal masses in an elastic collision change velocity by the same magnitude and that inelastic collisions result in proportionally decreased magnitudes in velocity). Student groups can use available technology (e.g., video, motion sensors, simulations) or physical measurements to gather data and information from their investigations (e.g., mass, displacement, time, initial and final velocities). Students can use mathematical and/or computational thinking to determine whether momentum is conserved in the system. For example, in a system of two objects, a decrease in momentum by object 1 is equal to an increase in momentum by object 2. Student mathematical representations can also be used to model and describe the total momentum of the system by calculating the vector sum of momenta of the two objects in the system, illustrating that momentum in the system is constant. Students can use the “I Notice, I Wonder” routine to look for data patterns between the initial and final states of the system. (Note that momentum, a vector, can have values in the negative direction.)

Momentum is a measure of the mass of an object times its velocity (p=mv), and it is defined for a particular frame of reference. In any system, the total momentum is always conserved. While the momentum of objects can change, those changes are balanced by changes in the momentum of objects outside the system. Momentum is often described for objects that collide with one another. The momentum of objects in an isolated, closed system is conserved during a collision. Systems can contain any number of objects and the objects that make up a system can stick together or they can come apart during a collision. The law of conservation of momentum states that the momentum of any closed, isolated system does not change. Using this law enables students to connect conditions before and after an interaction without knowing details of the collision. 

• Organized data includes defining the boundaries and initial conditions of a system with two interacting objects.

• Mathematical representations identify and describe the momentum of each object in the system as a product of its mass and velocity.

• Mathematical representations model and describe the physical interactions of the two objects in terms of the change in the momentum of each object as a result of the interaction.

• Mathematical representations use evidence to illustrate that the total momentum of a system of objects is conserved when there is no net force on the system.

Provide students with opportunities to apply knowledge and engage in the engineering process to create and revise a device to achieve a desired goal.

Careful observations of the data for the duration of time for collisions (sudden vs. extended) will provide evidence supporting the science idea that the average force experienced by an object in a collision depends on the duration (time) of the interaction. Educators can present students with a real-world engineering problem (e.g., car crashes, phones shatter when dropped, medical supply drops) that needs a solution to minimize the forces acting on the object(s) during a collision. To investigate these problems, students can gather data about the interactions occurring during the collision (e.g., using force sensors to measure impact differences, or egg drop challenges to protect an object). Students can design a device (e.g., helmets, parachutes, airbags, shipping containers) that reduces the net force applied to an object by extending the time the force is applied to that object during a collision. Student designs can include scientific rationale for their choice of materials used and for the structure of the device, and descriptions for how the device meets any criteria and constraints for the project (e.g., risk mitigation, costs, availability of materials, requirements set by society). Educators can provide students with opportunities to build, test, and evaluate the success of their designed devices based on its ability to minimize the force on the test object during a collision. Students can identify any unanticipated effects or design performance issues that the device exhibits. Test results can then be used by students to refine their initial designs and test for improvement. Revisions can include extending the impact time, reducing the device mass, and/or consider cost-benefit analysis. 

• Design applies scientific ideas to minimize the force an object experiences during a collision.

• Design meets identified criteria and constraints for the challenge. 

• Design is revised to demonstrate how an increase of time over which a collision occurs will decrease the force acting on an object.

• Design is revised to demonstrate how a decrease in mass of an object within a collision will decrease the force acting on the object.