Structures & Forces 

Structure:

ANY object that provides support

Structural Strength:

The ability of a structure to hold itself up, over and above any weight that is added.

Structural Stability:

The ability to maintain its position even if a FORCE is acting on it.

Force:

A push or a pull that tends to cause an object to change its movement or shape; measurement is Newtons

Three Structural Forms

1. Solid Structure
2. Frame Structure
3. Shell Structure

Solid Structure

• Formed from a solid piece of strong material

• Has little or no space between inside, relying solely on its own mass to resist any force that may be acted on it

• Usually the strongest of the three types of structures

Frame Structure

• Formed from a rigid arrangement of parts, or structural components, fastened together

• The strength of the frame comes from how these parts are placed together

• Lighter than solid structures because they use less material

Example: Skeleton

** Draw some examples of Frame Structure from your book

Shell Structures

• Has a solid outer surface, may be rounded or flat with a hollow inner area

• Rounded outer area are stronger due to the curved area distributing the load around the whole surface

• Hollow interior allows it to be lighter than solid structures

** Draw some examples of Solid, Frame, and Shell Structures from your book

Function:

• A structure's use or purpose

• Example: The function of an airplane or car is transportation

When a structure is built knowing the main function (i.e. comfort, transportation or shelter) of the structure will allow the designers to build it accordingly

Common Function BUT Different Design

Example: Roofs (pg 277) 

Common Function: provide covering for a building and protect what is inside

Different Design: because they are all effective but are suited for different environments (climate), cultures, resources.

Aesthetic:

The pleasing appearance /effect that an object has due to its design

1. On Page 277, Draw each letter and the corresponding type of housing that matches to a different part of the world.

2. On page 273 match the man made structures with that of natural structures.Describe similarities and difference.
   

Understanding Forces

Force:

A push or pull that tends to cause an object to change its movement or shape

The actual effect of a force relies on these three things:

1. Magnitude (amount of the force)

2. Direction (where the force is going)

3. Location (where the force is applied)

Break into groups of two, think of an action in sports (ex. kicking a soccer ball, sumo wrestling, etc.), act out the action, and explain the forces that are being exerted. Remember each force is comprised of a magnitude, direction, and location. 

Newton

Unit of Force is referred to as a NEWTON (N)

1 Newton (N) = amount of force needed to hold up a mass of 100 grams (g)

External Force:

A force which is applied on a structure by something else

• Walking into the ocean and waves hit your body

• The Earth's gravity is a force that pulls towards the center of Earth, therefore Gravity is an External Force

Mass:

Amount of matter in an object

• Greater the Mass = Greater the Gravitational Force on that object (it's heavier)

• Weight is actually the pull of gravity on a mass.

Centre of Gravity

Activity Time!!!!!!!

1.Everyone Stand up and find a place in the room
2.Hold your arms out straight for 2 minutes, What is happening?
3.Stand on one foot and try to keep balance, What are you experiencing?

Answer - GRAVITY! Is having an effect on your stability 

Centre of Gravity:

An imaginary point in any structure where the downward force of gravity acts.

Location of the centre of gravity will determine the stability of a structure

Symmetry:

Balanced ratio of mass which occurs on both sides of a line/plane or around the centre of the axis

The force of gravity on either side of the center point is equal

For a symmetrical structure to be stable, the mass of that structure must be distributed equally around the centre of the structure’s base, meaning force of gravity around the centre is also equal  

Structural symmetry helps balance the forces acting on a structure. 

Static and Dynamic Loads

When structures are built the idea of having weight put on them is something every engineer or designer must think about.

Load:

External force carried by a structure

Two Types of Loads

1. Static

• Weight of a structure and the non-moving load it supports

• Example: books on a bookshelf

2. Dynamic 

• External force that moves or changes with time

• Example: moving students on a staircase at school

Note: When you build a dynamic structure you must consider you may have both static and dynamic loads, therefore the structure must maintain both

Performance Requirements of a Structure:

• How well will a structure hold up under the load it was designed to carry out.

• Important for safety, cost and efficiency-Performance Requirements should always be expressed in Maximum Weight

Engineers need two conditions to decide what type of bridge is suitable:

1.What the bridge is crossing (water/land)
2.What kinds of loads the bridge will be supporting

Draw and Define each of the four different types of bridges. Google search "Edmonton Bridges" and label the bridges and the category of bridge. 

Internal Force:

• Forces that act within a structure

• One part of a structure exerts on other parts of the same structure

Three Types of Internal Forces

1.  Compression
2. Tension
3.  Shear

Compression:

A force that acts on an object or push parts together within an object

Tension:

A force that acts to stretch and pull apart something

Shear: 

A force which push parts which are in contact with each other in opposite directions

Poster Project

(you may partner up and use poster board or your own supplies) 

Create a poster with an example & a diagram explaining the following concepts:

• Symmetry

• Static Load

• Dynamic Load

• Compression Force

• Tension Force

• Shear Force

• Internal Force

• External Force

RUBRIC

Complementary Forces:

When different kinds of internal forces act on a structure at the same time

Example: Bending

• Compression is put forth on the top and tension is put forth on the bottom

• Failure to resist either results in the beam breaking
  

Strength in Shapes

A triangle is a strong rigid shape that cannot be bent. Where as rectangles and squares can be easily bent, and circles can compress and buckle outwards when force is applied. 

Structural Components

Arches:

Common structure used in bridges due to supporting large loads because the force of the load is carried through the arch to the foundation.

Beams:

Flat structure which is supported at each end.

Columns:

Solid structure that can stand by itself.

Breaking Point!

Structural stress:

Results when internal and external force are applied to a structure which can weaken it 

Structural failure:

Results when a structure can no longer stand up to forces acting on it

Structural fatigue:

Results in weakness to a structure when it is repeatedly used out of it’s original function 

Unit D Review