Topic 4

Question 1

What is an external force?

Answer 1

Act on a structure from outside
it

Question 2

What is an internal force?

Answer 2

Occur within the materials from which a structure is made. Can change the shape or size of the structure.

Question 2

What is deformation?

Answer 2

Change in shape or size of a
structure caused by forces.

Question 3

Name and describe the two types of external forces.

Answer 3

Dead Load
■ Permanent force acting
on a structure
■ Includes the weight of the
structure it’s self
■ Over time it may cause
the structure to sag, tilt or
pull apart
** Live Load**
■ Changing or non-permanent force
acting on a structure
■ Force of the wind, items in/on the
structure (furniture, people, snow,
rain)
■ Impact forces
■ Most structures are designed to
withstand a force 2 to 3 times the
expected live load

Question 4

Name and describe the 4 types of internal forces.

Answer 4

Tension: Stretch a material by pulling it’s ends apart
Compression: Crush a material by squeezing it together
Shear: Bend or tear a material by pressing different parts in
opposite directions at the same time
Torsion: Twist a material by turning the ends in the opposite
directions

Question 5

What is tensive strength?

Answer 5

measures the largest tension force
a material can withstand before breaking

Question 6

What is compressive strength?

Answer 6

The largest compression
force a material can stand before losing its shape or
breaking into pieces

Question 7

What is shear strength?

Answer 7

The largest shear force a material
can stand before ripping apart

Question 8

What is torsion strength?

Answer 8

The largest torsion force the
material can stand and spring back to its original shape