10.3 Force I can: -recognize force as a vector quantity that has both magnitude and direction. -describe friction as a force that opposes sliding between two surfaces and always acts in a direction that is opposite to the relative motion of the object. -calculate frictional force from a force diagram.

Force “Our football team is a force to be reckoned with.” Force: an action exerted on a body in order to change the body’s state of rest or motion; force has magnitude and direction. Examples: Throwing or catching a ball? What causes an object to accelerate?

Net Force Is the combination of all of the forces acting on the object. Objects accelerate in the direction of net force. If net force is 0, object will not accelerate.

Balanced Force Net forces= 0. Example: Equal match of tug-a-war, hat sitting on head, light hanging from ceiling. Other examples?

Unbalanced Force Forces acting on an object become unequal. Results in acceleration! Examples: 2 vs. 1 in tug-a-war

Friction Force that opposes motion between two surfaces that are in contact. Occurs between two surfaces are rough Hills and valleys Always opposes applied force. Always a bad thing? Parking brakes.

Not All Friction is the Same Static Friction: the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest. (Push but cant move) Kinetic Friction: the force that opposes the movement of two surfaces that are in contact and are sliding over each other. Sliding Rolling (less than sliding) Fluid Friction (air resistance)

Harmful Friction v. Lubrication Problem: Harmful Friction Cylinders moving in an engine Solution: Lubrication Motor Oil, grease, bearings.

Increase and decrease friciton If you want to reduce friction, make surface ___________. Smoother Swimmers and bikers wearing tight cloths. If you want to increase friction, make surface _____________. Rougher Baseball players wear batting gloves.

Cars What is bad friction in cars? Examples: What is good friction in cars? What is hydroplaning?