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Force of Gravity

Large objects have a greater gravity than smaller objects. Gravity or gravitational forces exist when one object attracts another. We're not talking about finding someone really cutey-wootie, awwww! We're talking about the molecules of one object pulling on the molecules of another object. It's like the Earth pulling on you and keeping you on the ground. That's gravity at work. Every object in the universe that has mass has a gravitational force. Even you exert gravity. When you compare your mass to the mass of the Earth, your gravitational force isn't very impressive. Sorry about that.

Earth's Gravity

Obviously gravity is very important on Earth. Other planets also affect our world. Our connection to the Moon's gravity makes the tides rise and fall. The Earth's gravity keeps our planet orbiting the Sun, just like the Sun's gravity pulls on our planet. When the earth spins and gravity pulls on the clouds, weather can be affected. We have to bring up an important idea now. The Earth always has the same pull on every object. If you drop an acorn, or you drop a piano, they will fall at the same speed. It is the Earth's gravity and pull that make objects speed up when they are falling. The Earth constantly pulls and objects constantly accelerate.

Feathers

"People always say, "What about feathers? They fall so slowly." Obviously, there is air all around us. When a feather falls, it falls slowly because the air is in the way. There is a lot of resistance and that makes the feather move slower. The forces at work are the same. If you dropped a feather in a container with no air (a vacuum), it would drop as fast as a baseball.

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Keywords for Review

Kinetic Energy: The energy of an object related to the motion of the object. On a simple level, an object that is not moving has no kinetic energy. An object that is moving has some amount of kinetic energy. The more an object moves, the more kinetic energy it has. An object increases its kinetic energy if it accelerates and increases its velocity. For example, as you increase the temperature of a gas, the molecules become more energetic and the system has an overall increase in kinetic energy. Kinetic Energy=(0.5)* mass * (velocity)2

Exothermic: A chemical reaction that releases energy after the reaction is complete. The energy is usually released as heat, but it can also be released as light or sound. On a small scale, a burning candle releases light and heat because of exothermic reactions as the wax burns. On a large scale, an explosion might occur when blasting with sticks of dynamite (TNT).

Activation Energy: The least amount of energy needed for a chemical reaction to occur. Reactions often require some amount of energy to get moving. For example, placing hydrogen and oxygen gases in a container will not give you water. There is a certain amount of energy required to get the first reaction going. Catalysts are substances that help to lower activation energies so that reactions can proceed.

Viscosity: A term used to measure the fluidity of a liquid. As the attractions between the molecules increase, viscosity increases. Fluids with high viscosities don’t flow easily. Some substances such as honey or sap are very slow moving and have high viscosities. Other fluids such as water or mercury (Hg) have very low viscosities.

Volatile: Volatility is the likelihood that a substance will vaporize (become a gas). Volatility measurements are all about comparing two substances. Substances with a higher vapor pressure are more volatile. Alcohol is more volatile than water because it evaporates at a lower temperature.

Reference Materials

Encyclopædia Britannica: http://www.britannica.com/EBchecked/topic/369668/matter
NYU.edu: http://www.nyu.edu/pages/mathmol/textbook/whatismatter.html
NASA: http://www.grc.nasa.gov/WWW/k-12/airplane/state.html
NASA: http://astroventure.arc.nasa.gov/teachers/pdf/AV-Astronolesson-Part2.pdf
Wikipedia: http://en.wikipedia.org/wiki/States_of_matter


 
RELATED LINKS
- Cosmos4Kids: Vacuum of Space
- Chem4Kids: Matter
- Chem4Kids: Astrochemistry
- Chem4Kids: Atoms
- Geography4Kids: Solar Radiation
- Biology4Kids: Scientific Method
- Physics4Kids: Magnetic Fields
- Physics4Kids: Light
- Physics4Kids: Gravity

- NASA: Home Page
- NASA: Kids Home Page
- ESA: Home Page
- ESA: Kids Home Page

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