What display will your class share?
2
Understanding ties
The shelves that your pupils might design for the display can be supported in two main ways - using ties or using struts.
Ties are the simplest to use because a tie can be nothing more that a piece of string that literally 'ties' the front end of a shelf back to a point on the wall above where the shelf it is resting against the wall. The angle of the tie is important.
The load on the shelf causes the tie to be stretched or put into tension. The smaller the angle between the tie and the shelf the greater is the load on the tie. You can check this out by 'pinging' the tie and listening to the sound it makes. The smaller the angle the higher the sound indicating that the tie is tighter and you know that the more you tighten a sting on a musical instrument the higher the note.
If the load on the tie becomes too large the tie will snap. The tensile strength of the tie will depend on the materials it is made from and the thickness of the tie. Cotton is not as strong as nylon. So a thin piece of cotton thread will be a weaker tie than a thick piece of cotton thread. Both these cotton ties will be weaker than a similar ties made from nylon. The length of the tie will NOT affect its strength.