Newton’s Second Law

Newton’s Second Law

http://www.youtube.com/watch?v=UyI3IL46yq4

Do-NowO Write down what you remember from

the lab on Friday.O What is the relationship between

force and acceleration? What is the relationship between mass and acceleration?

Force and Newton’s Second Law

O What is force?O Any push or pull

O When the force increases and the mass stays constant, the acceleration increases

O When the mass increases and the force stays constant, the acceleration decreases

Newton’s Second LawO Fnet = ma

O Fnet = force (in Newtons)O m = mass (in kg)O a = acceleration (in m/s2)

WeightO the effect of the

acceleration due to gravity

O Always directed downward

O Dependent on locationO Weigh more or

less on the moon? Why?

MassO Amount of matter

in an objectO Constant for a

particular objectO Independent of

locationO Do you have a

different mass on the moon?

Weight EquationO Fg = mg

O Fg = force due to gravity (in Newtons)

O m = mass (in kg)O g = acceleration due to gravity (10

m/s2)

Weight in an ElevatorO http://www.youtube.com/watch?v=2k-

2IlJcaHg

Net Force and Acceleration

O Net force: the result of all forces exerted on an object

O If forces are exerted in the same direction, they are added

O If forces are exerted in opposite directions, they are subtracted

O Acceleration is always in the direction of the net force (largest force)

O If the Net force is zero, the object is not acceleratingO Can it be moving though?

Free Body DiagramsO Drawing to help

understand forces

O Draw arrows away from the object to represent forces

EquilibriumO When the

acceleration of the object is zeroO Net force is also

zeroO Two types

O Static: Object is not moving

O Dynamic: Object is moving at constant velocity

Static ObjectsO If the net force is zero AND the

object is not moving, it is said to be staticO Weight pulls objects downO Normal force

O Supports them from fallingO Acts perpendicular to a surface

And now your favorite professor…

O http://www.youtube.com/watch?v=_XJrY2sKfFQ