Grade 5 · Forces Acting on Structures · Forces Acting on Structures
Help a Bridge Hold Its Load
External forces act on a structure from outside. Those loads create internal forces within the structure's parts, which can stretch, squeeze, bend, twist, or shear them.
Visual model
See how the ideas connect
Distinguish internal and external forces
Connect loads to structural effects
Choose features that reduce damage
Forces Acting on Structures
For students
Notice, predict, explain
Choose one part of the model. Predict how it connects to another part, then use the lesson evidence to explain your thinking.
For teachers
Pause for science talk
Show the model before the explanation. Ask “What do you notice?” and “What might change?” Then revisit student ideas after the worked example.
The big idea
Structures must transfer forces safely
A structure withstands loads when its shape, materials, joints, and foundation guide forces through a stable path without exceeding what its parts can resist.
Work it through
Follow a load across a truss bridge
- Step 1 The weight of traffic and the bridge itself create downward external forces.
- Step 2 Members in the truss experience internal tension or compression as they share the load.
- Step 3 Triangles help the frame keep its shape while transferring forces toward the supports.
- Step 4 Bracing, strong joints, and a secure foundation help the structure resist wind, vibration, and changing loads.