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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 Law
O 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 Equation
O 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
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