Chapter 18: Solids

Molecular Make-up Particles in a solid are packed tightly together and stay in a fixed position Solids have a definite shape and a definite volume Particles vibrate

Crystalline Solids Particles form a regular, repeating pattern Geometric shapes arranged in an orderly pattern Solids made of crystals

Crystalline Solids

Amorphous Solids Particles are not arranged in a regular pattern plastics, rubber, glass, etc.

Density Density = mass (gm or kg) volume (cm 3 or cc) What happens to the density of a chocolate bar when you break it in half? Weight Density = weight volume (Liquids)

Which is less dense, 5 kg or iron or 5 kg of leaves? The leaves, greater volume

Elasticity Elasticity refers to an object’s ability to change shape when a force is applied and then return back to its original shape when the force is removed. rubber bands, springs, steel, glass, plastic

Inelastic Materials Materials that do not return to their original shape when the force is removed. clay, putty, Play Doh, mashed potatoes, peanut butter

Elastic Limit Objects will not return to their original shape (permanently deformed) when the elastic limit is exceeded

Hooke’s Law The amount of stretch (or compression) is directly proportional to the force/weight applied. F = kx F = Force k = spring constant x = amount of stretch or compression

Hooke’s Law Lab

Compression and Tension I-beams Compression (strong): particles compress/squeeze together Tension (weak): particles stretch apart

I-Beams Compression and tension on top and bottom flanges Nearly same strength as solid beam, lighter

Neutral Layer in an I-Beam The neutral layer is in the center where there’s no compression or tension.

Scaling Can creatures such as Godzilla and King Kong really exist?

Scaling Scaling is the study of the relationship between strength and weight when objects are scaled up. Weight depends on volume Strength comes from the AREA of the cross section of the limbs

Scaling Weight (volume) increases at a faster rate than strength-A problem! If we double the size of something: –Volume = 2 3 or 2 x 2 x 2 = 8 –Area = 2 2 or 2 x 2 = 4

Some Questions Which cools a glass of lemonade faster, ice cubes or crushed ice? Which would you want to peel, 10 lbs. of large potatoes or 10 lbs. of small potatoes? Which would require more chocolate, 1 lb. of big strawberries or 1 lb. of small strawberries?

Answers The crushed ice 10 lbs. of large potatoes 1 lb. of small strawberries Why??

Because smaller objects have more surface area per kilogram. The crushed ice presents more surface area to the lemonade.