UNIT: PHYSICAL SCIENCE Chapter 9: Properties and Changes of Matter PHYSICAL PROPERTIES OF MATTER WHAT IS MATTER? • Matter- included solids, liquids, and gases. • Examples: mountains, footballs, lakes, clouds, and air. • Mass- amount of matter in an object. • Measured in units of grams (g) or kilograms (kg). • Weight- the amount of the pull of gravity between the object and Earth • An object with a large mass normally has a large weight. A balance is used to measure mass. DENSITY • Why does oil float on water? • Density- the amount of mass in a given space. • You can find the density by • Finding the mass • Finding the volume • Dividing the mass𝑚𝑎𝑠𝑠 by the volume 𝑔 (𝑔) 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑐𝑚3 = 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑐𝑚3 ) • When an object is placed in a less dense liquid or gas, the object will sink to the bottom. • When an object is placed in a more dense liquid or gas, the object will float to the top. • If the object has the same density as the liquid or gas, it will “hover” in place. WHAT ARE PHYSICAL PROPERTIES? • Properties- things you can observe with your senses. • Odor, hardness, color, shine, mass, density • Physical Properties- can be observed without changing the identity of the substance. • When you describe a rock, the rock is not changing into something else- it stays the same. • Examples: density, the substance’s ability to conduct electricity, magnetism • A substance’s state, whether it is a solid, liquid, or gas, is another important physical property. WHAT IS A PHYSICAL CHANGE? • When heat turns a solid into a liquid or a liquid into a gas, the identity of the substance is unchanged. • Physical Change- a change in size, shape, or state without forming a new substance. • Example- an ice cube melting to liquid water. • Different substances are in different states at room temperature. These substances also change state at different temperatures. • Melting Point- temperature at which a substance changes from a solid to a liquid. • Boiling Point- the temperature at which a substance changes from a liquid to a gas. • Freezing Point- the temperature at which a substance changes from a liquid to a solid. • All of these temperatures vary from substance to substance. WHAT ARE MIXTURES? • Mixture- any combination of two or more substances keep their own properties. • Examples: tossed salad, chocolate milk • Even though the substances in a mixture keep their own properties, you may not always recognize these properties • Example: Milk is a mixture. If you add vinegar to milk it will separate the substances making up the milk. TYPES OF MIXTURES • Suspension- a mixture made of parts that separate upon standing. • Example: Oil and water • Can sometimes be separated using a strainer • Emulsion- a suspension of two liquids that usually do not mix together. • Example: the few seconds after you shake up oil and water • Colloids- contains undissolved particles or droplets that stay mixed in another substance. • Examples: Fog is a liquid-in-gas colloid, Smoke is a solid-in-gas colloid • Solution- a mixture of one substance dissolved in another so that the properties are the same throughout. • Example: Kool Aid mixed in water. • The Kool Aid particles are soluble- they can be dissolved in water. When it is poured into the water it is a solute- substances that can be dissolved. • The water is the solvent- part of the solution that dissolves the solvent. • Alloy- solutions of one or more metals and other solids. • 14-carat gold- an alloy of gold, copper, and silver • Sterling silver – an alloy of silver and copper. • Pennies are made of an alloy of copper and zinc WHY DO THINGS FLOAT? • Pressure- the weight or force on a given area. • When an object is submerged in a fluid, the fluid “pushes” in on the object. • The push is greater at the bottom than on the top, so the fluid pushes the object toward the surface. • This push is called buoyant force. • The amount of buoyant force equals the weight of the water that is displaced. • Example: water rising when you get in a bathtub • Buoyant force varies on the weight and density of the object.