Mass

Mass Definition and Units Mass is the amount of matter in an object. Remember that matter is made of atoms and molecules? So mass is basically all of the atoms and molecules in an object. The basic unit of mass is grams (g). A kilogram (kg) is equal to 1,000 grams. A milligram (mg) is 1/1,000 of a gram.

Mass Mass vs. Weight Summary And just to make sure you finally got it… Mass is the amount of matter something has - all of the “stuff” it is made of. Mass is all of those atoms and molecules that make up the matter. Let’s take this ball for instance: Notice how the ball has the same number of molecules on the Earth as is does on the moon. The ball has the same amount of matter and therefore the same mass in both places. = =

Mass Mass vs. Weight Summary Weight is how gravity pulls down on the matter in an object. The gravity on Earth pulls on the matter in the ball harder than the gravity on the moon. Therefore, the ball has more weight on Earth. = 6 lbs = 1 lb

Mass Measuring Mass So now that you know the difference between mass and weight, let’s review how mass is measured. Mass is measured using a tool called a triple beam balance. It’s called a triple beam balance because it has three beams with different measurements on it, and to find the mass of an object you have to balance two marks right here. 3 beams

Volume

Volume Definition & Units Volume is the amount of space something takes up. Think back to your lesson about the phases of matter. One of the characteristics of both solids and liquids is that they have their own volume. Gases have the volume of the container they are in. There are two units of volume: milliliters (mL) and centimeters cubed (cm 3 ). Measuring cup clip art licensed from the Clip Art Gallery on DiscoverySchool.com DiscoverySchool.com

Volume Measuring Cubed Solids To find the volume a cubed or rectangular solid multiply the length, width, and height (LxWxH). The units for cubed solids are cm 3. Make sure when you measure the length, width and height of an object that you do it in centimeters and not inches.

Volume Measuring Liquids To find the volume of a liquid, all you have to do is a straight measurement - pour the liquid into a container that shows the measurements. The liquid measuring cups that your mom uses in the kitchen measure liquid volume. In science, the best way to measure liquid is with a graduated cylinder or a beaker. When measuring liquid volume, use milliliters (mL) as the units.

Volume Meniscus When you measure volume with a graduated cylinder, you have to watch out for the meniscus. A meniscus is a dip in the graduated cylinder caused by water sticking to the sides of the graduated cylinder. Always read the volume of the liquid at the bottom of the meniscus. Image from Chem PagesChem Pages Meniscus

Volume Measuring Irregular Solids How would you find the volume of this rock or these nails? There are too many sides of the rock to measure with a ruler, and the nail changes size as you get closer to the tip. The best way to measure these objects would be to use a measuring method called water displacement.

Volume Water Displacement How Water Displacement Works: 1. Fill a graduated cylinder to a known measurement. 2. Drop the object being measured into the graduated cylinder. 3. Look at the new volume. 4. Calculate the difference between the first and second volume. The difference equals the volume of the object. Or…

Volume Water Displacement 1. Fill a container with a spout (like a liquid measuring cup) full to almost overflowing with water. 2. Place another container beneath the spout to catch the water. 3. Place the object to be measured in the container with water. Water should spill out into the catching container. 4. Measure the water that spilled into the catching container. The volume of the overflow water will equal the volume of the object. Overflow water spills into the “catching container”. Measuring cup filled to almost overflowing. Overflow water measured in a graduated cylinder to find the volume of the object. Measuring cup clip art licensed from the Clip Art Gallery on DiscoverySchool.comDiscoverySchool.com

Density

Density Definition and Units Density is the amount of matter in a particular space. Essentially, density is a combination of mass and volume. To find the density of an object divide the mass of the object by the volume. The units of density are g/cm 3 or g/mL. Density tells us how compact or close together the molecules in an object are. The closer the molecules are, the more dense the object.

Density Understanding Density Think about this: Which is heavier, a pound of rocks or a pound of cotton balls? Trick question, right? Both are a pound so they weigh the same! Which one do you think would take up more space though? A pound of rocks or a pound of cotton balls?

Density Understanding Density A pound of cotton balls would take up a whole bunch more space than a pound of rocks. That’s because the pound of cotton balls is less dense than the pound of rocks.

Density Understanding Density The molecules in the rocks are much closer together and more compact than the molecules in the cotton balls. The rocks have same mass and take up less space than the cotton balls, therefore the rocks are more dense.