Isaac Newton

Newton’s First Law• "Every body perseveres in its state of being at

rest or of moving uniformly straight forward except insofar as it is compelled to change its state by forces impressed." (Principia)

• An object in motion will remain in motion and an object at rest will remain at rest unless acted on by an outside force.

• Inertia

Newton’s First Demo

Newton’s Second Law• "A change in motion is proportional to the

motive force impressed and takes place along the straight line in which that force is impressed.” (Principia)

• First Part: When I push something, the distance it moves depends on how hard I push it.

Second Part: If I push something, it moves in the direction that I pushed it.

The Most Useful Equation

• Newton’s Second Law:

(Force = derivative of momentum)

€

F = dpdt

Newton’s Second Law Derived

€

p = m *v : dpdt= d(m *v)

dt= m * dv

dt+ v * dm

dt

€

m = mass : dmdt= 0

€

F = m * dvdt

€

dvdt= a : F = m * a€

F = dpdt= Δ momentum

Δ time€

F = dpdt= Δ momentum

Δ timeF = ma[F]=[m]*[a]

[m]=kg[a]=m/s2

[F]=kg*m/s2=Newton

Special Case: Gravity

F = maFGravity=mgg=9.8 m/s2≈10

m/s2

Newton’s Third Law

• "If one object exerts a force on another the other exerts the same force on the one" (Principia)

• “For every action there is an equal and opposite reaction!”

• ACTION = -REACTION

Newton’s Third Law: Falling

FEarth on Bubar= FEB FBubar on Earth= FBE

Newton’s Third Law: Falling

FEB FBE

FEB=Fgravity

FEB=mBubar*a

FEB=mBubar*g

FEB=70 kg*10 m/s2

FEB=700 Newtons

FEB = -FBE

FBE=FEB=700 N

FBE=mE*aE

aE=FBE/mE

aE=700 N/6E24 kg

aE~1E-22 m/s2

a Bubar= 10 m/s2 : a Earth=0.0000000000000000000001 m/s2

Earth on Bubar Bubar on Earth

Hero Engine

Fwa

FwaFwa

Fwa

Fac

Fac

Fac

Fac

RECALL• Newton’s First Law:

Inertia• Newton’s Second Law:

F=ma• Newton’s Third Law:

Action=-Reaction

Wolf 330

Questions?

• Lesson, demonstrations and additional resources located online at:

http://bubarnewtonslaws.wikispaces.com/

• Your welcome to try demos after class !