Forces That Can Act on Structures (Notes)

Forces That Can Act on Structures

• Structures constantly experience forces; they must be designed to withstand the forces they will face (Force: any push or pull)
• If the structure isn’t strong enough it may experience structural failure.
• If the structure is too strong, time and resources may have been wasted.

Internal and External Forces

• External force: acts on an object from outside the object; e.g., wind, gravity, earthquakes
• Gravity
• is a natural force of attraction
• acts on all structures all the time
• pulls structures towards Earth’s centre

• other external forces
• a person on a ladder
• pulling a drawer open
• sitting on a chair
• cars on a bridge

• Internal force: one part of a structure acting on another part of a structure; e.g.,
• tension in stretched cables on a bridge
• compression by the weight of a roof on the walls

External Forces and Loads

Every structure supports a load

• Total load: the sum of all the static and dynamic loads
• Static load: the effect of gravity on a structure (the weight of the structure itself) also called dead load
• Dynamic load: the force that moves or changes while active on the structure
• Called “dynamic” because they change their magnitude, direction, and point and plane of application.
• Wind is considered a dynamic load because its magnitude can change

E.g., a bridge: The static load is the weight of the bridge itself (dead load).

The dynamic load is the weight of the moving cars across the bridge (also called live load).

DRAW PICTURE OF TRUCK ON BRIDGE WITH LABELS HERE

Internal Forces

• Can be classified as:
• Compression – a force that squeezes or presses something together
• Tension – a force that stretches apart to expand or lengthen
• Shear – a force that pushes in opposite directions
• Torsion – a force that twists
• Bending – A force that acts to bend a component putting one side of the part in tension and the opposite side in compression

Structures: Form and Function Notes

Structures: Form and Function

Structure: something made up of parts that are together in a particular way for a specific purpose or purposes

Form: the basic shape of the structure

Function: the job that the structure does

Force: Any push or pull that can make an object change shape, speed, or direction

Ergonomic design: designs that take into account information about the human body. Ergonomic design can help people from getting hurt doing repetitive tasks and those who are physically challenged

Classification of structures

Structures can be classified by their:

Function – it may contain something (a glass), support something on top (a wall), or span a space (a bridge)

Construction – how they are built and what they are built from

Form – solid, frame and shell structures also there are combination structures

Solid Structures

Most are solid all the way through, but some may have small hollow parts, e.g., an apple or a mountain.

Frame Structures

Made of parts and fastened together; the parts are often called structural components. E.g., a bicycle, a tennis racket, cars, skeleton, umbrellas.

Shell Structures

Strong and hollow structures e.g., an igloo, a domed roof, a glass; these make good containers and require few materials. Even clothes are considered shell structures.

Combination Structures

Combination of frame, shell and solid structures. E.g., a house is made of solid pieces of wood that are arranged in frame. The boards arranged in a frame provided strength to the house. 

Form and Function Answers

Considering Form and Function 

Structure	Description of Form	Description of Function
Desk	Made from wood and metal It has a rectangular flat surface with four circular legs	Used to support books, binders and to provide a surface to write on.
Chair	Four legs, sometimes attached to the desk. Made from plastic and metal. Has a back support and a surface to sit on, has four legs	Used to support our bodies in a sitting position
Coat Rack	Made from wood, metal or plastic Its shape is a tall pole with a wider base; there are hooks at the top	Used to hang coats and other clothing, to hang bags
Pen	Made from plastic. Hollow container holds the ink in a stick-like shape.	Used to write with using hands
Bulletin Board	Piece of cork board attached to the wall with a metal frame. Large thin rectangular shape.	Used to display work, art or information
Shelves	Made from wood    The shape is a rectangular prism open on one side, there are flat wooden boards inside	Used to support books or other objects
Binder	Made from plastic, cardboard, and metal. Plastic covers the outside of rectangular cardboard.	Used to store and organize papers

Science Safety Test Outline

The test outline is as follows:

1. Identify the problems and solutions in the image

2. Know what WHMIS means and the names of its symbols

3. Know what HHPS means and the names of its symbols

Know precautions for HHPS products

4. Study the names of the science equipment in the package and their uses and safety precautions

5. Review the safety features in the lab; for example, the eye wash station, fire extinguisher, etc. and know what to do when a problem occurs in the lab.

Good Luck!

Links to WHMIS and HHPS Prezis

Here is some reference material about WHMIS and HHPS that I created for you.

WHMIS
http://prezi.com/ko5q-owcjchz/whmis/

HHPS
http://prezi.com/mmtahrfhlj1d/hhps/

Science Safety Test Tuesday September 16

 7A, 7C, 7D, 7E, will have their Science Safety Test on Tuesday September 16th.

7B will have their Science Safety Test on Wednesday September 17th.

A study guide will follow.

Science Equipment Sample Answers

Science Equipment

Equipment	Name	How is it used	Safety Procedures
	Beaker	Contain, heat, measure, pour liquids, test tubes, or powders	It’s fragile, be careful when handling
	Hot plate	Used for heating substances	Makes sure it cools completely; use gloves or tongs to handle hot beakers
	Graduated cylinder	Measuring liquids and powders	Don’t overflow, use a funnel. Be careful not to tip over
	Test tube	Testing and observing liquids and powders	Use test tube rack for support. Be careful it’s fragile.
	Funnel	Pour liquids into smaller openings	Pour slowly to avoid an overflow, support the funnel
	Beaker tongs	For picking up hot beakers	Pick up beaker between the middle and the top
	Microscope	Viewing microscopic objects	Very expensive and fragile
	Triple Beam Balance	Measuring weight	Meant for light objects
	Thermometer	Measuring temperature of substances	Very fragile
	Stirring rod	For stirring substances	Very fragile
	Erlenmeyer flask	Containing and heating liquids	Fragile, do not heat a sealed container

Science Safety Activity Sample Answers

Grade 7 Lab Safety Activity                        Name ______________

The drawing you received depicts unsafe procedures in the school laboratory. Answer the following questions based on this illustration and the safety guidelines listed in your textbook on pages xviii to xx.

1.       List 6 unsafe activities shown in the laboratory drawing

a.       Fire extinguisher is blocked by the chair

b.      Girl is smelling fumes directly from the test tube

c.       There is a broken test tube and other objects on the floor

d.      There is food on the table

e.      There is spilled liquid on the floor

f.        There is a lot of mess in the lab

2.       Explain why each activity is unsafe

a.       In case of fire, you would not be able to access the fire extinguisher quickly

b.      The fumes may be harmful to her nose, or worse-she should be wafting the fumes toward her

c.       The students may be cut by the broken glass and possibly trip over other objects

d.      Food may become contaminated with poison or bacteria which would harm the student when the food is ingested

e.      Someone can slip and fall if not cleaned up immediately

f.        Equipment can be damaged and books on table can be damaged

3.       Name 3 safety guidelines from your textbook that are not illustrated in the drawing

a.       Handle sharp objects carefully

b.      Treat all living things with respect

c.       Report safety concerns to teacher

4.       Read each statement and print T for true and F for false on the line provided

__F_____           The biology laboratory is a good setting for practical jokes

__F_____           The teacher is responsible for lab clean-up

__T_____           Spilled chemicals should be wiped up immediately

__F_____           It’s unnecessary to report minor laboratory accidents

__F_____           Performing experiments not assigned by a teacher is good creative procedure

__T_____           No chemicals or other materials should ever be tasted

__F_____           Be sure to smell materials directly from the beaker

__F_____           Only the teacher needs to know the location of the first aid kit

__F_____           Always throw broken glass into the garbage can once cleaned up

__F_____           Lab materials are inexpensive so do not be concerned if they break       

5.       What procedure would you follow in each of these situations

a)      Clothing on fire

Use the body wash station and someone inform the teacher

b)      Hot water spill on hand

Use the body wash to run cold water over burn, someone informs the teacher

c)       Particle in your eye

Use the eye wash station to rinse eyes for 15 minutes, inform the teacher

d)      Cut from broken glass

Inform the teacher, wash with soap and water, teacher provides Band-Aid 

e)      Group member not following safety procedures

Inform the teacher immediately 

f)       Beaker accidentally breaks on the floor

Inform the teacher and he/she will clean up the glass

g)      Your group is not sure of how to do an experiment

       Ask the teacher

How to Access the Textbook Online

You must first log in to www.sciencesource.ca

1. Select the Grade 7 Textbook
2. Select "Log in" on the left side
3. Enter the log in: ClassFollower
4. Enter the password: Follower
5. Select the unit you would like to study; we are beginning with unit B Structures
6. The e-book chapters are listed on the page