Physical Property: Buoyancy - sink or float?

When an object floats, it can stay on the surface of a liquid by itself. Different solids, liquids, and gases can float. For example, both cork and oil will both float on the surface of water. Some gases, such as helium, can rise, or “float” in the air. When an object sinks, it moves down with gravity. Different solids, liquids, and gases sink. For example, a solid coin will sink in a cup of water. Gases that are heavier than air, such as propane and butane, can sink as well.

Displacement explains why objects sink or float. Displacement occurs when you place something in a fluid, or any substance that flows, and it moves the fluid out of its way. You can watch displacement at work when you drop an object in a cup of water and the water level rises. Gravity pulls the object down, but the difference in pressure above and below the object causes an upward force. The object pushes the water out of its way, making the water rise. An object will sink if it weighs more than the water it pushes away, and an object will float if it weighs less than the water it pushes away. The Greek mathematician Archimedes discovered that the amount of water displaced by an object depends on the mass of that object. Mass is the amount of matter in a substance, and dense objects have more mass than less dense objects. Dense objects that do not displace much water will sink, while less dense objects that displace a lot of water will float.

Shape can also help an object float. A ball of clay will sink, but a canoe shape made from the same amount of clay can float because it displaces more water. A canoe shape can push more fluid out of its way in relation to its weight. The amount of air inside of an object can also help it float. Boats can float despite the heavy and dense materials used to build them because of the large amount of air inside the hull. Hollow objects, such as table tennis balls or an empty plastic bottle, are able to float better than solid objects.

Many children believe that heavy objects sink and lighter objects float. Some heavy objects like boats float, while relatively lighter objects such as coins sink. Why do you think these objects sink and float? Think about it and describe observations you have made of sinking and floating objects.

 

Physical Property: Buoyancy - displacement.

Did you ever notice that when something floats in water, part of it is actually under water? As it sinks (even a little bit) it pushes away the water until that amount of water weighs the same as the thing that is floating.

If the thing you try to float is too heavy, it cannot push away enough water to be the same as how much it weighs. If that happens, the thing will sink.

Ask an adult to help you with an experiment (a test) that can show you how this works: Float a small plastic boat in water and notice how deep the boat sinks when it is empty. Then add pennies to the boat and watch how the boat sinks deeper and deeper the more pennies you add. The pennies make the boat weigh more and more. If you add enough pennies, the boat will sink deep enough so that water reaches the top and then the whole thing sinks.

Blow up a balloon and float it on water. It will not sink very far because it is not very heavy. If you look really close, where the balloon touches the water, you can see a little dent in the water under the balloon. That's the place where the water is pushed out of the way. If you try this test with a ball that is exactly the same size as the balloon, the ball will sink deeper before it floats. Because the ball is heavier than the balloon, it has to push more water out of the way before it can float.

It is not just how heavy something is that makes it float or sink. Look how heavy real boats are -- and they still float. Floating or sinking has to do with the amount of water pushed out of the way. Any boat will sink if you put enough stuff inside it -- just like your experiment showed. Small, heavy things like a marble or a rock cannot float because they cannot push enough water out of the way to be the same as how much they weigh..

So remember, anything that floats weighs the same as the water pushed out of the way.

Physical Property: Strength

The strength of a material is its ability to withstand an applied stress without damage. Strength refers to the point which the material begins damage or break from a force applied to it and the damage cannot be reversed when the force is removed. The applied force may be from pulling, pushing, or twisting.

Physical Property: Hardness

Hardness refers to various properties of solid materials that have high resistance to various kinds of permanent shape change when a force, such as hitting or pulling, is applied. In science, there are three main types of hardness:

• Scratch hardness: Resistance to changes on the surface, like scratches, due to friction from a sharp object;
• Indentation hardness: Resistance to changes due to pressure from a sharp object;

• Rebound hardness: Can an object bounce off the material when dropped on it.

Physical Property: Malleability and Ductility

Malleability refers to a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling.

Ductility refers to a material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire.

Properties of materials (matter).

Bread Mould Experiment with Crazy Chris!

Fungi growth - The Private Life of Fungi

Bread Mold Speed Frame

Bread Mold Hyphae

Why does Bread Mold?

We’ve all seen it. You stick a loaf of bread in your breadbox or pantry, and a few days later you begin to notice blue, green and black fuzz growing on top of it. Bread mold is a common problem, and can actually be the source of many interesting science experiments. But why is a loaf of bread such a desirable source for mold? The answer lies in an understanding of exactly what mold is, where it is found and how it survives.

What is Mold?

Mold is a member of the fungi kingdom, which is a separate categorization from plants and animals. Mushrooms also fall into this category. Fungi can be defined as a plant without chlorophyll, so it cannot get energy directly from the sun. This means that fungi must use other plants and animals as its food source. This is why bread mold is so common – because of the ingredients in bread, it is an excellent source of nutrition for many molds to grow and thrive. It also contains limited moisture content, which is why mold can grow so well instead of bacteria or yeast that requires higher moisture levels to survive.

Bread and Mold Meet

Bread and mold often meet through the mold spores that are in the air. Although you cannot see them, there are probably millions in the air around you. These spores can accumulate in the dust around our home, which is kicked up through cleaning or even someone walking by. The spores can then settle on your bread and the bread molding process will begin. Mold will not only live and feed on bread, it will also reproduce there. This is why you see bread mold spread throughout your loaf if you let it sit there long enough. Mold reproduces as long as it has a nutrient source – sometimes it can double in size in an hour’s time.

Growing your Own Bread Mold

Growing bread mold is not hard to do. You can use a slice of bread that has been rubbed along the floor or other dusty surface, and give it a couple of squirts of water from a spray bottle to moisten it. Place the bread in a sealed bag and leave it in a dark place for a few days. You will find that you are able to grow your own bread mold garden with relative ease and in a fairly short period of time. It’s a great way to bring science into your home!

The Bread Mold Experiment

The aim of the bread mold experiment is to see what organisms are living on the kitchen bench and compare this to what is picked up from just the air alone.

Materials Needed:

·     You will need the following:

·     2 slices of bread (wholemeal is best)

·     cling wrap or sealing sandwich bags

·     spray bottle filled with water

·     magnifying glass (optional)

Procedure:

Step 1: Wipe one of the two slices of bread on the kitchen bench or any other surface regularly used for food preparation. The second slice acts as a control for the first; it shows what would happen without wiping it on the surface.

Step 2: Spray both slices very lightly with water

Step 3: Seal the slices in separate pieces of cling wrap or separate sandwich bags.

Step 4: Place the wrapped bread slices somewhere warm and wait for the mold to grow. Once the difference between the two slices is significant enough, remove them and inspect the results.

Step 5: Examine the mold colonies with a magnifying glass. Note that caution must be taken not to breathe in the dust from the mold colonies as it can cause medical complications.

What is Happening?

The mold colonies have ended up on the bread either from landing on the bread from the air, or as a result of being collected from the bench in the process of wiping. The difference in the quantity and types of mold present show that wiping the bread on the bench results in far greater mold growth as well as diversity.

Possible Extension: Activity to Test Disinfectants

This bread mold experiment can be extended to test different brands of disinfectants. Select up to four different brands of disinfectants you have at home. Example, Dettol, Lysol, bleach, etc.

Treat four pieces of bread, each with a different brand and leave them in the open. Record your observations.

Opening Entry

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