A Refresher on Density
Last year we learned about density, or the amount of mass in a given space. We also learned that as more heat energy is added, particles vibrate more, become less dense and can change from a solid to a liquid to a gas. Below is your Intermediate webpage explaining this. I'm adding it to refresh your memory. It is NOT assigned, but certainly recommended should you feel you need it.
STATES OF MATTER
1. States of Matter
Click on the picture above to play with an interactive on States of Matter
2. How molecules move in different states of matter
Click on the picture above to play "Change It". You can also see how pressure and temperature interact to change states of matter in by clicking on this NOVA link.
3.Test your knowledge
See if you can win the "Millionaire" game.
Things you should know about mass, weight, gravity, & density
- Mass is the amount of matter in an object. Weight is the amount of matter multiplied by gravity (or the amount of force with which an object is attracted to the Earth).
- Gravity is the force of attraction between two objects with mass. The larger and closer the object, the greater the attraction. That's why an apple falls to the earth. To learn more about gravity, check out this webpage called "Gravity Facts". Because Earth is a more massive object than the Moon, an object of the same mass weighs more on Earth than it does on the less massive moon.
- Density is the amount of mass in a particular space or volume. The more mass in a given space, the more dense it is. It's easy to think that an object floats or sinks based on how heavy it is, but mass is only part of it. Whether an object floats or sinks has to do with how the mass is packed into a space. The more mass in a given space, the more dense it is. Objects that float are less dense than the fluid they are floating in. They'll sink if they are more dense than the fluid. The image on the left shows how various liquids float above or sink below another fluid. The more dense fluids (such as honey) will layer below the less dense fluids (such as karo syrup). The fluids are layered from the most dense at the bottom to the least dense at the top.
- Adding heat energy to a substance causes its molecules to vibrate more. The more they vibrate, the more space they take, the less dense they become. That's why cold water sinks below warmer water. The cold water molecules aren't vibrating as much as the warm water molecules, so they take up less space, and are more dense. Most substances in their solid form are more dense than their liquid form, which is more dense than their gaseous form. Interestly, water is wonky because it is at its most dense at 4 degrees Centigrade - just above freezing, or 0 degrees Centigrade. That's why ice floats on water.
- Less dense substances float above more dense substances
- When the earth was a molten mass early in its formation, the more dense nickel and iron sank (to the core) below the less dense rock of the crust.
- The oceanic crust is mostly made up of a rock called basalt, which is more dense than the granite rock of the continental crust, That's why the oceanic crust is lower than the continental crust