Chapter 13

Forces

What is Force?

•A push or pull•You are exerting a force right now (against the chair, or against the atmosphere)

•Other objects are also exerting a force on you!

What are the Four Forces?•Electromagnetic

•Strong•Weak•Gravity

A force:• Gives energy to an

object• Causes objects to:

1.start moving2.stop moving3.change direction4.change shape

Two forces:• Can be exerted in the

same direction (add together)

• Can be exerted in opposite directions (subtract them)

Net Force:

Balanced vs. Unbalanced:• Balanced = forces in

opposite directions that are equal

• Unbalanced = total force is in the same direction - changes the motion of an object

Balanced

Unbalanced

Friction:• A force that opposes motion• Will cause an object to slow

down & finally stop• When two surfaces touch

each other, there will always be some friction because the surface face is not completely smooth

Friction:• The amount of friction

between two surfaces depends on how hard the surfaces are pushed together & the type of material of the two objects

• A heavy object will force the two surfaces together more than a lighter object

Friction:

• To move an object, the force you exert on an object in one direction must be greater than the force of friction on that object in the opposite direction

Types of Friction:1.Sliding – solid objects

slide over one another2.Rolling – an object uses

wheels or ball bearing to roll over another object

3.Fluid – object moves across or through a fluid (all gases & liquids)

What type of friction?

What type of friction?

What type of friction?

Putting it all together: