Forces

CONTACT FORCES Contact Forces: is a force that is exerted only when two objects are touching. A. FRICTION D. COMPRESSION B. BUOYANT FORCE C. TENSION E AIR RESISTANCE

CONTACT FORCES A. Friction: the force that one surface exerts on another when the two rub against each other. Examples: Sliding friction ( when solid surfaces slide over each other) Rolling friction ( when an object rolls over a surface) Fluid friction ( when an object moves through a liquid or a gas) The strength of the force of friction depends on two factors: the types of surfaces involved and how hard the surfaces push together.

CONTACT FORCES B. Buoyant force: the upward force exerted by a fluid on a submerged object. The buoyant force acts in the upward direction, against the force of gravity, so it makes an object feel lighter Weight of the object is greater than the buoyant force = sink Weight of the object is less than the buoyant force = begin to sink to displace a volume of fluid with a weight equal to its own. Weight of the object is exactly equal to the buoyant force, the two forces are balanced.

CONTACT FORCES C. Tension: force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

CONTACT FORCES D. Compression: A pushing or pressing force that is directed toward the center of an object. Math Activity: p. 201

CONTACT FORCES E: Air Resistance: the fluid friction experienced by objects falling through the air. The greater the surface area of an object, the greater the air resistance. Air resistance increases with velocity. Eventually, the force of air resistance becomes large enough to balances the force of gravity. At this instant in time, the net force is 0 Newton; the object will stop accelerating. The object is said to have reached a terminal velocity.

NON-CONTACT FORCES Non-Contact Force: Force exerted by one object on another even when the objects are not touching. A. ELECTRICAL FORCE B. MAGNETIC FORCE C. GRAVITY

NON-CONTACT FORCES A. Electrical force: The force exerted by stationary objects bearing electric charge on other stationary objects bearing electric charge. If the charges are of the same sign, then the force is repulsive; if they are of opposite signs, the force is attractive Static electricity (lightning) Current electricity

NON-CONTACT FORCES B. Magnetic force: A force that exists between two electrically charged moving particles.

NON-CONTACT FORCES C. Gravity: the force that pulls objects toward each other. Free fall: the motion of falling objects when the only force acting on it is gravity. Acceleration due to the force of gravity is 9.8 m/s/s. The size of the force depends on mass (matter, doesn’t change) and distance. The gravitational force Earth exerts on an object is the weight ( is a force, changes if its distance from earth changes) of the object.

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