Section 2

Force

Force – push or pull

• a force always acts in a certain direction• ex. if you push something, the force is

in the direction of the push

Forces in Nature

• Electric force• ex. lightning

• Magnetic force• ex. magnetic poles

Weight is a force

Newton

• Unit used for force (N)

Net force• The combination of all the forces acting on an object.• How do you determine the net force of an object if all

forces act on the same direction. • The answer depends on the directions of the forces

Ballanced and unbalanced forces• When the forces on an object produce a net force of 0 N, the forces

are balanced.• Balanced forces do not cause a nonmoving object to start moving.• When the net force on an object is NOT 0 N, the forces on the object

are unbalanced.• Unbalanced forces are necessary to cause a nonmoving object to

strat moving.

What is friction?

• Friction• force that opposes the motion of an

object• the force of friction works in the opposite

direction of the force of motion

Friction occurs because the surface of any object is rough

• The amount of friction between two surfaces depends on many factors.

• Two factors include the force pushing the surfaces together and the roughness of the surfaces.

Types of Friction• Kinetic Friction

• The word kinetic means “moving” , friction between moving surfaces

• In which of the two pictures friction is smaller?

Static Friction• When a force is applied to an object but does no

cause the object to move.• The word static means ……….

CLASSWORK

• IN YOUR OWN WORDS, WRITE A DEFINITION FOR THE TERMS FRICTION AND FORCE.

• LIST THREE FORCES YOU EXCERT WHEN RIDING A BICYCLE.

• EXPLAIN HOW FRICTION CAN BE HARMFUL AND HELPFUL.

• EXPLAIN WHY FRICTION OCCURS.• NAME TWO WAYS IN WHICH FRICTION CAN BE

INCREASED.• LIST THREE COMMON LUBRICANTS.• NAME SOME WAYS TO REDUCE FRICTION.• MAKE AN ILLUSTRATION EXPLAINING WHAT KIND OF

FRICTION IS BEING APPLIED.

THANK YOU