Mass, Volume & DENSITY

Weight Scientific Definition: Weight is the vertical force exerted by a mass as a result of gravity Definition: Weight is how heavy something is…how much it weighs.

Weight is not constant! Weight changes depending on the pull of gravity. i.e. The farther an object is from the center of the Earth (or the center of the gravitational force), the less weight the object has. Feels MORE gravity; weighs MORE. Feels LESS gravity, weighs LESS.

Standing on Earth causes you to weigh more than standing on the moon Standing on Earth causes you to weigh more than standing on the moon. This is because the moon has less gravity than the Earth…it pulls you to itself less than the Earth does. The moon is smaller than the Earth. Gravity is also the reason we have air to breathe.

Objects in space are said to become weightless Objects in space are said to become weightless. This is because the distance between the center of the Earth and the object is too great to cause a gravitational pull. However the object is not massless. This is why the people float when in space, they are too far away from Earth to feel the effects of gravity. People on the moon can jump far distances because the gravity on the moon is less than on the Earth.

Standing on the top of a mountain causes you to weigh less than standing at sea level. Standing on top of Mount Everest, the highest mountain in the world, will cause you to weigh less than anywhere else in the world. This is also why it is harder to breathe at the top of Mt. Everest…the gravity is less able to keep air near the ground.

Units of Weight lb (pound) kg (kilogram) g (gram) N (Newton) = force Gravity = 9.8N To find weight, use a scale.

Mass Definition: Mass is the amount of matter in an object. Less mass More mass = 1 molecule

Mass is constant!! Mass does not change unless matter is added or removed from an object. Mass does not change when shape or location is changed. A car has the same mass in Los Angeles as it has in New York City.

People add mass by eating and remove mass by exercising.

1 oz of fluid has the same mass if it is in a test tube or in a petri dish.

Units of Mass g (gram) kg (kilogram) To find mass, use a balance.

Volume Definition: Volume is the amount of space an object takes up.

Units of Volume L (liter) mL (milliliter) cm3 (centimeter) Volume is used everyday, when you buy things in the store. e.g. milk is measured in liters. e.g. cough syrup is measured in milliliters.

To find the volume of a regular shaped object, use these formulas: Cube = lwh Sphere = 4/3πr3 Cylinder = πr2h Prism = 1/2bhH Cone = 1/3π r2h

It is difficult to measure the densities of odd shaped objects It is difficult to measure the densities of odd shaped objects. To find their densities, place them in a known amount of water. The amount of water that changes (or is displaced) is the volume. Measure this water to find the volume of the ball.

Another way to find the volume of a small odd shaped solid is to place it in a known amount of water in a graduated cylinder. The new volume is the volume of the water + the solid. The difference between the volume of the water and the new volume is the volume of the solid. The amount the volume changes is the volume of the solid. The volume of the water is 5mL. The new volume of the water + the solid is 7mL. 7mL – 5mL = 2mL. The volume of the solid is 2mL.

To find the volume of a liquid, use a graduated cylinder. Remember to read the volume at the meniscus.

Density Scientific Definition: Density is the mass per unit volume of a material. Definition: Density is how much “stuff” in a given space. All matter has density, even gas. Density can be used to identify an object.

Each sample of the same liquid has the same density. i.e. density never changes Each different liquid has its own density. i.e. density is a property of matter Each sample of solid has its own density.

Units of Density Density is expressed in g/mL or g/cm3 g = grams mL = milliliter cm3 = centimeter cubed

You can use the formula or a graph to determine density.

Density can be used to compare two objects with the same volume. A piece of steel and the piece of wood with the same volume have different densities…the wood is less dense than the steel (the steel feels heavier than the wood).

Density and Floatation Density determines if an object will float or sink in a liquid. Objects with greater density than the liquid will sink. Objects with lesser density than the liquid will float.

Water is more dense than ice. Both are made of H2O Water is more dense than ice. Both are made of H2O. This happens because as water freezes, its molecules spread out, becoming less dense. The density of ice is about 89% of the density of liquid water. This means approximately 11% of the ice will stay above the water. This is what makes icebergs so dangerous.

How to figure out if something will float: Dsolid > Dfluid Object will sink. Dsolid < Dfluid Object will float. For example: If a piece of gold has a density of 12.4 g/mL, will it float of sink in water? Answer: the gold will sink. For example: If a piece of aluminum has a density of 0.79 g/mL, will it float or sink in water? Answer: the aluminum will float.

Liquids can float on one another, depending on whether or not they are soluble in each other.