Forces and Friction

THINK! In the clip, what causes the tractor to start moving?

FORCE: action exerted on a body in order to change the body’s state of ___________________________. A __________________ or a ___________________ Cause acceleration or deceleration! (You can’t change your motion without a force) Force is a __________________________ (has magnitude and direction). Units are __________________________

NET FORCE: the ___________________ ___________________ ___________________ ___________________ acting on an object. If net force is zero, object will ________ accelerate (it stay at rest or constant velocity). Force of the bat’s legs holding it up Force of gravity pulling down

BALANCED FORCES: More than one force acting on an object that has a net force equal to ________ Forces are equal in _____________ and opposite in _________________________ Objects affected by balanced forces either: Do NOT MOVE or Move at CONSTANT VELOCITY (__________________________ __________________________) 100 N east 100 N west Net force = ___ 100 N west 100 N east Net force = ___

UNBALANCED FORCES: More than one force acting on an object that has a net force UNEQUAL to _____________ Have a net force that does NOT ______________________ Must be present to cause any change in an object’s state of __________________ or __________________. Causes the ____________________________ to change (acceleration or deceleration) west east Net force = ________

THINK! Balanced or unbalanced? A parked car: A car at a constant speed: A car accelerating:

Balanced or Unbalanced? Net Force = 100 N right 100 N left Will the truck accelerate? Balanced or Unbalanced? Net Force = 100 N right 60 N left Will the truck accelerate? Balanced or Unbalanced? Net Force = south Will the plane accelerate? north

FRICTION

THINK! How do you know friction is at work in this clip?

Occurs between ________ surfaces FRICTION: Force that opposes _______________________ between two surfaces that are in contact. Occurs between ________ surfaces Molecular Adhesion Surface roughness ___________________ the applied force. Converts kinetic energy to _________________________ For motion to change, the force applied to an object must be ____________________________friction 100 N west Net force = _______ 100 N east

Net Force ________ Net Force _______ Net Force _______

TYPES OF FRICTION STATIC FRICTION: resists the initiation of motion between two surfaces that are in contact and ___________________. Static friction is ____________________________kinetic friction. KINETIC FRICTION: opposes the movement of two surfaces that are in contact and are ______________________. There are 3 types of kinetic friction you need to know: SLIDING FRICTION: Two objects _______________________ each other ROLLING FRICTION: Round object rolling over a flat surface FLUID FRICTION: Force that resists the movement of a solid object through a fluid (________________________________).

Static Friction Kinetic Friction The point where the object starts moving and the friction goes from static to kinetic Kinetic Friction

THINK! What are the 2 types of friction? How are they different?

Sliding Friction Rolling Friction Fluid Friction

Drag is fluid friction that affects cars, airplanes, boats, etc.

THINK! In each clip what type of friction do you see? How do you know? Clip 1: Clip 2: Clip 3:

Friction can be _______________________ Necessary to walk, hold an object, strike a match, etc. Important for braking Causes excessive heating or wear of moving parts Decreases fuel efficiency

WAYS TO REDUCE HARMFUL FRICTION Replace sliding friction with __________ friction Use _________________ Use ______________________________ Make surfaces ________________

WAYS TO INCREASE HELPFUL FRICTION Make surfaces _______________________ Add __________________________________ Increase _______________ on two objects (Example: adding ______________________ _____________________________________)

THINK! What is one way that friction can be good? What is one way that friction can be bad?