Forces in 1 Dimension

Chapter 4

4.1 Force and Motion• Force is push or pull exerted on object• Forces change motion

– Makes it important to know the forces on an object

• Force diagrams (free body diagrams) show all forces acting on object– Both direction and magnitude – vector– Define system

Contact and Field Forces• Contact – touching• Field – non-contact

(not touching)

• Every touch generates force

• Table 4-2, pg 94

Force and Acceleration• Forces change motion• Newton’s 2nd Law

– a = Fnet/m

– Net forces and mass will affect the acceleration of an object• Applying a force changes the object’s motion –

generates an acceleration• Changing mass, changes forces

Newton’s 1st Law• “An object that is at rest will remain at rest,

and an object that is moving will continue to move in a straight line with constant speed, if and only if the net force acting on that object is zero”

• Inertia – tendency of an object to resist change– Not a force

• Equilibrium – net force on object is zero

4.2 Using Newton’s Laws• Weight – gravitational force acting on object

– Changes depending on where you are in Universe

• Scales – How it Works, pg 110• Apparent weight – weight changes with

motion– Example: elevator– Weightlessness – apparent weight is zero

• No contact forces pushing up on object

Drag Force• Particles of air exert forces on an object

– Often is a huge force• Drag force – force exerted by a fluid on an

object moving through the fluid– Direct relationship – increase speed, increase

drag force– Affected by size and shape of object, and

temperature and viscosity of fluid

Terminal Velocity

• Constant velocity is reached when drag force equals gravitational force

4.3 Interaction Forces• Interaction pairs• Newton’s 3rd Law states that all forces come

in pairs– One doesn’t cause the other– Because there is one, there is the other– Equal in magnitude and opposite in direction– 2 force diagrams – each one contains one of the

forces in the interaction pair

The Normal Force• Support force• Perpendicular

contact force exerted by a surface on another object

Lab• Force table lab• Newton’s second lab