By Nicole and Keri

Table of Contents:

1. Causes if Friction
2. Stratic Friction
3. Sliding Friction
4.Rolling Friction
5. Fluid Friction
1. Universal Gravitation
2.Factors Affecting Gravity
3. Weight and Mass

Causes of Friction:
Definiton: Fricton is the force that two surfaces exert on each other when the rub against each other. The causes of friction depends on two different things. The first factor is how hard the surfaces push against each other and the second is the types of surfaces involved. These two factors combined creates Friction. For example, skiers have very little friction between their skies and the snow. Without friction, a moving object might not stop until it strikes another object in its path ( Jones 43).


Stratic Friction:

Stratic Friction is the friction that acts on objects that are not moving. Because of this type of friction you must use extra force to start a stationary object like a car. For example, pushing a heavy desk. If you push the desk with less force than the floor, the stratic force between the desk and the floor, the desk would not move. To make the desk move you have to exert to work greater force than the stratic friction (Jones 44).

Sliding Friction:

Sliding Friction occurs when two solid surfaces slide over each other. For example, when you spread sand on an icey path, it would improve your footing. Another good example would be when ballet dancers apply a stickey powder to the sole of their ballet shoes so they won't slip (Jones 44).

Rolling Friction:

Rolling friction occurs when an object rolls across a surface. When I roll across the floor with roller skates, the skates are a great exmaple of rolling friction. All Skates, skateboards, and bikes are a great example for rolling friction. Engineers use ball bearings to reduce the friction between the wheels and the rest of the bike/skateboard/skates. These ball bearings are small smooth steal balls that reduce friction by rolling between moving products such as the bike, skateboard, and roller skates (Jones 44).


Fluid Friction:
Fluid friction occurs when a solid object moves through a fluid. Examples of this specific friction are water, oil, and air. Just like rolling friction, fluid friction is a lot easier to conquer than sliding friction. This is the exact reason why the parts of machines must slide over each other are often bathed in oil. This is also one of the ways that helps the solid parts move through the fluid instead of sliding against each other ( Jones 44). Friction by karebear_9

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Universal Gravity:

Defintion: Gravity is a force that pulls objects toward each other. Newton, a mathmatician and physicist, realized that gravity acts everywhere in the universe, not just on Earth. For example, it is the force that makes a ball fall back down to Earth. It is the force that keeps the Moon orbiting the Earth. It is the force that keeps all the planets orbiting the Sun. What Newton realized is now called The Law of Universal Gravity. Universal Gravity states that the force of gravity acts between all objects and the Universe. This means that any two objects in the universe, without exception, attracted to each other (Jones 45)

("Gravity Diagram")
("Gravity Diagram")

Factors Affecting Gravity:
Two different factors affect the gravitational attraction between objects: mass and distance. Mass is the measure of the amount of matter in an object. The more mass an object has, the greater its gravitational force. Gravitational force depends on the distance between the objects. The farther apart two objects are, the lesser the gravitational force between them (Jones 45).

Weight and Mass:
Mass is a meaure of the amount of matter in an object. Measure is a measure if the gravitational force exerted in an object. The force on gravity on a person at the surface of the planet is known as weight. For example, when you step on a bathroom scale, you are determaining the gravitational force on Earth is exerting from you. Weight varies with the strength of gravitational force but mass does not. Also say you weigh about 450 newtins on Earth. When you travel to the moon you weigh yourself on the moon and you weigh about 75 newtons- the weight of about 8 kilograms on Earth. You weigh less on the moon because the moon's mass is only a fraction of Earth's (Jones 46).

"Gravity Diagram." Web. 18 May 2011. <>.