GRAVITY AND FRICTION TYPES OF FORCES The push

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?