Abstract

Objective

To change the number of layers in a wood laminate to test for a change in the amount of load that can be supported.

Introduction

One important part of studying physics is the study of forces, and how forces affect matter. One force you may have heard of is the force of gravity, which pulls us towards the earth. There are many different types of forces that exert themselves on an object.

A load is a kind of force that exerts stress on the parts of a structure. When you stand on your skateboard, you are exerting a downward force on the board, which causes stress and strain on the materials used to build the board. This type of load is called a live load, and it is very important that a structure be able to fully support a live load in order for it to be safe. When a structure is too weak to support a load, it can break due to the stress and strain that the forces exert on the parts of the structure. This can cause a bridge or building to collapse.

Engineers use the laws of physics to calculate how the forces of a load are distributed between the parts of a structure. There are two main types of forcers that need to be balanced in a structure. Compression forces push inward upon an object in a structure. Tension forces are forces that pull out from the center of an object. When you stand on your skateboard, your weight causes a load to be placed on your board, which results in compression forces on the surface of the board, and tension forces on the underside of your board.

If your board has been poorly constructed and cannot balance these forces, then the board will break under the load. One way that engineers can balance these forces is by using a laminate, or sandwiched layers of material, to distribute the forces under load. By using laminates, engineers can make structures much stronger without making them too heavy. This is great for a snowboard or skateboard, because the board will stay light and flexible for doing tricks.

In this experiment, you will use wood and glue to make a series of wood laminate beams to test whether increasing the number of layers in a laminate will make it stronger.

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• laminate
• fibers
• force
• load
• compression
• tension
• bending
• twisting
• stress
• shearing

Bibliography

• Robinson, Lowell. 2005. "Skateboard Science." Exploratorium, San Francisco, CA. 12/24/05.
  http://www.exploratorium.edu/skateboarding/
• 2001. "Building BIG: The Labs." WGBH Educational Foundation, Boston, MA. 12/24/05.
  http://www.pbs.org/wgbh/buildingbig/lab/index.html
• Dawson, Donna. 2004. "Engineering Insights: 'Boards built strong to last longer; Durable snowboards - no longer an oxymoron." Composites Technology. Ray Publishing, Wheat Ridge, CO. 12/24/05.
  http://www.compositesworld.com/ct/issues/2004/December/687

Materials and Equipment

• wood glue
• balsa wood sticks in these sizes and quantities:
  • (1) 1/2" x 1/2" x 36"
  • (2) 1/2" x 1/4" x 36"
  • (4) 1/2" x 1/8" x 36"
  • (8) 1/2" x 1/16" x 36"
• bucket with a handle
• bathroom scale
• sand or gravel for weight
• 2 chairs

Experimental Procedure

1. First you will need to prepare your laminate beams of balsa wood and allow these to dry for a few days before conducting your experiments.
2. You will need to glue your strips of balsa wood together in the following combinations:

3. Using a paintbrush, apply a thin layer of glue to one side of each strip of balsa wood to be glued together. Place glued sides together and press until strips have adhered along the entire length of the wood strip. Wipe away excess glue with a napkin.
4. Cover your laminate strips with wax paper, and place books on top to keep the strips weighted down and flat while drying.
5. Allow strips to dry for 1–2 days.
6. After strips are completely dry, you can set up your experiment to test their strength.
7. Place two chairs, backs toward each other about 1 foot apart.
8. Take your strip of balsa wood and suspend the empty bucket in between the two chairs by resting the ends of the wood on the backs of the two chairs with the handle of the bucket looped over the middle of the beam.
9. Slowly pour sand or gravel into the bucket until the wood bows. As the wood begins to bow in the middle, it is a good idea to add cupfuls of sand, rather than pour the sand, until the wood breaks. Don't let the bucket fall to the ground or spill!
10. Weigh the bucket with the sand still in it on the bathroom scale to record the amount of weight required to break the wood. Write this down in a data table.
11. Repeat with all of your wood beams, recording the weight each time in a data table.
12. Make a graph of your results and look for a relationship between the number of strips in the laminate and the strength of the beam. Which beam was the strongest? Which beam was the weakest?

Variations

• Another important factor in beam strength is the length of the beam. Try to vary the length of the beam to see how that changes the amount of weight that the beam can support without breaking.
• When making laminates, one important factor is the type of glue used to adhere the materials together. Some types of epoxy or resin are much stronger materials than regular wood glue. Try an experiment to compare different types of glue products from your local hardware or hobby store.
• The fibers found in a piece of wood are what give it strength. You may notice these fibers when you look at a piece of wood and see the grain, or pattern that the fibers make. Different types of wood have unique patterns of fiber, which give different types of wood unique properties. You can see how strength varies in different types of wood, are some species of wood stronger than others? What do you think the difference is between a hardwood and a softwood?
• Another issue when dealing with the strength of wood is the orientation. Is it being used vertical for a post? Or is it being used horizontal as a beam? Is one orientation stronger than the other? Find out if strength is a function of orientation of the beam by comparing laminations (and wood grain) parallel to floor vs. perpendicular to floor

• For more science project ideas in this area of science, see Materials Science Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2006-02-02 13:40:09