Lesson 3: Net Force and Free Body Diagrams

How can I represent forces interacting on one object with a visual model?
How will an object move if it is interacting opposing forces?
What kind of forces cause an object to change speed or direction?
Will an object experiencing forces always be in motion?

Net force
Free Body Diagrams
Sum of Forces
Gravity
Lift
Thrust
Drag
Air resistance

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.
PS2.A: Forces and Motion
Each force acts on one particular object and has both strength and a direction. An object at rest typically has multiple forces acting on it, but they add to give zero net force on the object. Forces that do not sum to zero can cause changes in the object’s speed or direction of motion. (Boundary: Qualitative and conceptual, but not quantitative addition of forces are used at this level.)
PS2.B: Types of Interactions
Objects in contact exert forces on each other.

NGSS Cross Cutting Concepts:
Developing and Using Models
Planning and Carrying Out Investigations

Common Core State Standards Connections:
ELA/Literacy -
RI.3.1 Ask and answer questions to demonstrate understanding of a text, referring explicitly to the text as the basis for the answers. (3-PS2-1)
W.3.7 Conduct short research projects that build knowledge about a topic. (3-PS2-1)
W.3.8 Recall information from experiences or gather information from print and digital sources; take brief notes on sources and sort evidence into provided categories. (3-PS2-1)
Mathematics -
MP.2 Reason abstractly and quantitatively. (3-PS2-1)
MP.5 Use appropriate tools strategically.
(3-PS2-1)
3.MD.A.2 Measure and estimate liquid volumes and masses of objects using standard units of grams (g), kilograms (kg), and liters (l).
Add, subtract, multiply, or divide to solve one-step word problems involving masses or volumes that are given in the same units, e.g., by using drawings (such as a beaker with a measurement scale) to represent the problem. (3-PS2-1)

Students will practice modeling using free body diagrams how objects will multiple forces acting on them will move.
They will use these visual models to figure out how to calculate the overall net force on a given object. Students will make predictions on how objects will move or not move based on the calculated net force.
Students will then examine 4 forces that act on objects in flight: lift, drag, gravity, and thrust. Students will explore the definitions of those forces, add those interacting forces to their observation journals of their own rockets, as well as experienced by paper airplanes they will make.

Students will deepen their understanding of balanced forces and the pattern of motion of all observable objects.

Students may think that objects that are not in motion are not experiencing forces.
Students may have a hard time conceptualizing the subtraction of opposing forces and the addition of forces acting in the same direction.

Tiered Assignments, Flexible Groupings, Choice boards for paper plane construction, Scaffolded Instruction, Graphic organizers, Formulas Provided, Student choice

Checkpoint

Net Force and Free Body Diagrams Practice

Forces During Flight Practice

Paper for airplane constructions

Written and video directions and models of how to build a paper air plane

Distance Measuring Tools