1. Forces
Internal and External

2. Forces Many forces act on objects and structures in the world.
Some are Internal (from inside the object)
Some are external (from outside the object)

3. External Forces:
Any pressures or forces that act from outside a system
Examples:
Gravity
Snow on a roof
A push or pull

4. Internal Forces
Compression: the reduction in volume and increase in pressure of an object or substance
Tension: stretching or straining
Shear: unaligned forces pushing one part of an object in one direction, and another part in the opposite direction
Torsion: the twisting of an object

5. Compression
Basically, the force of something being squished

6. Tension
Something stretching

7. Shear
Unaligned forces pushing in opposite directions

8. Torsion
Something twisting

9. Properties of Forces Magnitude: the force’s strength
Direction: the direction that the force is acting, usually represented by arrows
The thickness of the arrow represents the forces strength, and the point shows the direction

10. Mass vs. Weight
Mass: the quantity of matter in an object; measured in things like grams (g) or kilograms (kg)
Weight: the force of Earth’s gravity acting on an object; measured in newtons (N)

11. Loads A load is a force acting on a structure
There are 3 kinds of load
Dead Load: a static load caused by the weight of the structure on itself
Live Load: a static load caused by the weight of the objects it supports
Dynamic Load: any load on a structure not caused by gravity (example: wind or rushing water)