Google Classroom Assignment
Read the Layers of the Earth webpage first to refresh your memory about what we covered in class. Then read and do the interactives on this webpage. When you finish reading this page, you should be able to answer the questions on the right.
- What 2 things affect how strongly two objects are attracted to each other gravitationally? Explain HOW they affect gravity.
- What is your weight on Earth? Using the "Your Weight in Other Worlds" interactive, choose another "world" and report your weight on that world. EXPLAIN why you weigh differently on that world. When your weight changed, did your mass change, too?
- What two things affect the density of a substance? EXPLAIN HOW they affect density.
- If water behaved like all other substances, what would happen if I put ice cubes in a glass of water? What really happens when I put ice cubes in a glass of water? Why does water not behave like other substances?
- Using your own words, explain why learning about density helps us understand why the Layers of the Earth layered as they did. Explain with examples.
- Play the Millionaire game and see if you can win!!
Things you should know about matter, gravity and density
- Matter is something that has mass and occupies space (The smallest building blocks that make up matter are atoms)
- Mass is the amount of matter in an object.
Mass is NOT weight, although we often talk about something being heavier if it has more mass. To know how they are different, you have to learn about gravity first.
- Gravity is the force of attraction between two objects with mass. The larger the mass, the greater the gravitational force. And the greater the distance between the objects, the lesser the gravitational force.
That means that all objects attract each other. The more massive (use the words, 'more massive' because 'bigger or larger' can imply a bigger volume rather than greater mass) the objects are, and the closer the objects are to each other, the greater the attraction. That's why an apple falls to the earth. The Earth is very massive and attracts the apple, you, trees and even the air to it. Gravity pulls inward towards the center of the object (the center of gravity). On Earth, the center of gravity is the core. So, the closer (shorter distance) you are to the center of gravity or core, the greater the gravitational force. - Weight is the amount of matter (mass) multiplied by gravity (or the amount of force with which an object is attracted to another object - like the Earth).
When you stand on a scale, it is actually measuring the gravitational force of attraction between the Earth and the object (you) that is standing on it. The more massive you are, the greater the gravitational force between you and the Earth, so you weigh more! Because Earth is a more massive object than the Moon, an apple would weigh more on Earth than it does on the less massive moon because gravitational force on Earth is stronger. But the apple would still have the same mass (unless you took a bite out of it!!) And if you were to go out into space further away from the Earth, gravitational force is MUCH weaker because of the increased distance between you and the massive Earth. Your weight would be nearly zero, or you would be "weightless." But your mass hasn't changed - you still have all four limbs, a head and a body - but there is much less gravitational force on that mass. That's why astronauts float around in the space station!
Explore your weight in other worlds, check out the interactive below!
Density and States of Matter
What is Density??
Density can be defined 3 ways:
|
Density of matter in its different states
There are 3 states of matter: solid, liquid & gas
(We won't get into plasma, for those of you who have heard about it). With few exceptions, a substance, when it is a solid, is more dense (more packed together) than its liquid state, which is more dense than it gaseous state. (see the illustration on the left) |
Things that cause density of a substance to change
What happens when roads expand too much in the heat!
Roads are built with expansion joints or seams (spaces between the concrete slabs) which are designed to make room for the concrete slabs of the road to expand (become less dense) with the heat.. Sometimes, on long stretches of very hot days, the cement slabs expand so much that the seams aren't wide enough for how much the concrete expands. This causes the slabs to press against each other until they can no longer take the pressure, causing the road to buckle as they did in the image on the left. See what happens when a Wisconsin driver (see this link) didn't see it and went airborne (but wasn't hurt) after a long, very hot spell of 100 degree F + days.
Play with the Phet interactive "States of Matter" below to view how particles vibrate as you change thermal energy or pressure.
Test your knowledge! "Millionaire's" Game
Float or Sink? A Rule for What Floats
Floating or sinking - It's easy to think that an object floats or sinks based on how heavy it is, but mass is only part of it. Remember in our experiment, the heavier (more massive) orange bouncy ball floated, while the very lightweight (less massive) paper clip sank in water. Whether an object floats or sinks has to do with how much mass is packed into a space or volume. In other words, the density of the object is what is important.
Rule for what floats: Objects that float are less dense than the liquid or gas. They'll sink if they are more dense than the liquid or gas. That's also why cold water sinks below warmer water. The cold water particles aren't vibrating as much as the warm water particles, so they take up less space, and are more dense. Most, but not all, substances in their solid form are more dense than their liquid form, which is more dense than their gaseous form. Water is the exception. See "Water is Wonky" below. |
Water is wonky!
Interestingly, water is wonky (unusual) because it is at its most dense at 4 degrees C when it is still a liquid. Water freezes into a solid at 0 degrees C. Therefore, the solid form of water (ice) is actually less dense than its liquid form. That's why ice floats on water instead of sinks.
Water is also unusual because it is that it is the only substance that exists naturally on the planet in all 3 states of matter.
Think about it. What if rock existed in all 3 states of matter on the surface of our planet? Or the air we breathe?
Water is also unusual because it is that it is the only substance that exists naturally on the planet in all 3 states of matter.
Think about it. What if rock existed in all 3 states of matter on the surface of our planet? Or the air we breathe?
Look at the table on the right. It shows that the density of water is greatest (1.0000 g/ml) at 4 degrees C when water is a liquid. At 0 degrees C, when water is solid ice, the density is actually lower (0.99987 g/ml.) As the water nears the boiling point, when it becomes a gas at 100 degrees C, the density decreases (0.95865 g/ml.) |
Experiment with different density materials
Experiment with interactive on the left to see how different materials of different masses and volumes float or sink in water.
Remember that the density of water is 0.99802 g/ml at room temperature! NOTE: Your computer may not be able to run this Phet interactive. Don't worry if you can't. You can rely on our worksheets and experiments for this information. |
What does density have to do with Layers of the Earth???
|
The oceanic crust is mostly made up of a rock called basalt, which is more dense than the (silicate) granite rock of the continental crust. Remember, the uppermost part of the mantle and the crust are together called the lithosphere. "Lith" means rock, which describes the lithosphere - rocky. The less dense lithosphere floats atop the more dense asthenosphere. The oceanic lithosphere, being more dense than the continental lithosphere, sinks lower on the asthenosphere.
You can compare this to the bouncy ball and the styrofoam ball we saw during our class demonstration. The water was a model of the asthenosphere. The bouncy ball modeled the oceanic lithosphere, which floated much lower in the water. The Styrofoam ball modeled the continental lithosphere, which floated higher in the water. Even though both are less dense than the water and float, one is more dense (bouncy ball) than the other (styrofoam) . Similarly, that's why the oceanic lithosphere floats lower on the asthenosphere than the continental lithosphere.
You can compare this to the bouncy ball and the styrofoam ball we saw during our class demonstration. The water was a model of the asthenosphere. The bouncy ball modeled the oceanic lithosphere, which floated much lower in the water. The Styrofoam ball modeled the continental lithosphere, which floated higher in the water. Even though both are less dense than the water and float, one is more dense (bouncy ball) than the other (styrofoam) . Similarly, that's why the oceanic lithosphere floats lower on the asthenosphere than the continental lithosphere.