Gravity and Friction

Types of Forces The push or pull of an object is a force Some forces are applied only when objects touch but some forces can be applied when objects do not touch A contact force is one where the objects are touching while a noncontact force is one where the objects are not touching

Forces have both strength and direction and can be represented by an arrow. The length of the arrow represents the strength of the force. The SI unit of force is the Newton (N) Gravity is an attractive, noncontact force that exists between all objects that have mass Mass is the amount of matter in an object

The Law of Universal gravitation Developed by Sir Isaac Newton, the Law of Universal Gravitation states that all objects are attracted to each other by a gravitational force; the strength of the force depends on the mass of each object and the distance between them When the mass of an object increases, the gravitational force increases The gravitational force decreases as the distance increases

Weight-a gravitational force Weight is the gravitational force exerted on an object Because the moon has 1/6 less gravity than Earth, you would weigh 6 times less on the moon than what you would weigh on Earth. Your mass would stay the same, but your weight would change

Friction Friction is a force that resists the motion of 2 surfaces that are touching Static friction prevents surfaces from sliding past each other; acts on objects not moving; must use extra force to get a stationary object moving Sliding friction opposes the motion of surfaces sliding past each other Fluid friction is between a surface and a fluid; friction between a surface and air is air resistance What causes friction and how can it be reduced?