Friday, November 7, 2014

Thursday, November 6, 2014

Bridge Competition!

Efficiency rating = Weight it can hold (up to 15 kg) / Weight of the bridge

Bridge HW Grade based on:

25% Design

Creativity (your own design? or just something from the internet?)
Aesthetic appeal
Homogeneous distribution of weight

25% Use of materials (what material did you use, and why?)

Cost efficiency (the cheaper the better)
Strength/weight ratio
bonding agents & designs

25% Efficiency rating

Class weighted; Top 33% = A, next 33% = B, lowest 33% = C

25% Adhere to all of the rules

It's long enough for the span?
It is able to be loaded with the 5cm loading block?

Prize:
Person with the highest efficiency rating in each class does not have to take the final.

Basic set-up:
A 5cm by 5cm by 2 cm wood block with a hook in the center will support the weight (see the top green arrow)

Weight will be added to your bridge by adding sand to a bucket suspended to your loading block.

TuTh:
18 inch span

Wed. night
3feet span

** Your bridge will need to be slightly longer than what it needs to span! Span = the distance between the tables your bridge will be resting on.

Rules:

The bridge will just rest on the table surface - you cannot anchor it with duct tape etc.

You can make your bridge out of any material you want, but remember efficiency is determined by your bridge weight, so choose materials carefully!

Failure will be defined by either the bridge breaking, or deforming more than 5 cm.

You will need to fully load your bridge in 8 minutes or less.

Tips:

Pay attention to your joints - make the connections solid!

Use clothespins, bent hairpins, paperclips, or small C-clamps (from the dollar store) to hold pieces together while it dries:

Wax paper makes a great building surface - the glue won't stick to it.

Build it in sections - don't try to build it all at once!

Bring your bridge in to test:

Tu/Th class - Thursday 11/13/2014
Wed class - Wed 11/19/2014

Good luck!Wed
#1:

Saturday, November 1, 2014

6.12 Machines

Review:
General Problem Solving techniques:

FBD's

6.12 Machines:

Examples:6.122, 6.131, 6.145

HW: 6.123, 6.132, 6.147

6.9-6.11Multiforce members & Frames

Statics Lecture 20: Two-force and Three-force Members

Frames and Machines Example

Problem Solving Method:

1. Draw a FBD of the entire frame
2. Dismember the frame, and draw a FBD of each member.
3. First consider the 2-force members.
4. Consider multiforce members
     a.) multipforce connected to 2-force
     b.) multiforce connected to multiforce

5. Determine all internal forces
   a.) 3 equilibrium equ's / FBD
- Choose carefully where to take your M around!
Try to get only one unknown in your M equ.
- T or C??? Guess it is T, then pay attention to your signs!

Examples: 6.75, 6.87 a), 6.88 a)