 Describe how forces act upon objects and create motion  Describe how friction influences the motion  Explain the different types of friction  Explain why friction is important

 Is an _____ exerted on an object in order to change the object’s ________ or ______  A push or pull in other words  It has magnitude & direction  What does that mean?  Force can be balanced or unbalanced

Balanced Forces Unbalanced Forces  Balanced forces occur when the forces applied to an object produce a net force of zero  They do not cause a change in the motion of an object or move an object out of rest  Example: a hat on your head  Unbalanced forces occur when forces do not cancel out completely  They cause a change in the motion of an object  Because the net force is greater than zero the object will accelerate in the direction of the greater force

 Friction is the force that opposes motion between 2 surfaces that are in contact  Friction happens because the surface of any object is rough (microscopically speaking)  Friction opposes the applied force on an object  Friction also affects objects that aren’t moving

 When a car is accelerating, the forces are __________________ › The force moving the car forward is greater than the opposing force of friction  When a car is cruising at a constant speed, the force moving the car forward is ___________ by the force of friction  Balanced forces could also mean that the car is not in motion

Kinetic Friction  Is the force of friction against an object already in ______  There are different kinds of kinetic friction › Sliding friction › Rolling friction › Fluid friction Static Friction  Is the force of friction opposing the initial movement of an object from ________________  It is _______ than kinetic force

 ___________ is the friction that occurs between objects that are sliding past each other  ____________ is the friction of a round object rolling over a flat surface › It is usually less than sliding friction  ___________ is the friction of a moving object traveling through a fluid (a liquid or a gas) › It can be minimized by very smooth surfaces › When air is the fluid, the force of friction is called ___________

 Why is friction important?  How can friction cause problems?

1.Using lubricants such as motor oil, wax and grease › Lubricants are usually liquids but can be solids or gases 2.Replacing sliding friction with rolling friction › Such as using ball bearings between wheels and axles 3.Make surfaces smoother

1.Making surfaces rougher 2.Increase the force pushing the surfaces together