Download Newton`s 3 Laws

Sir Isaac Newton’s Three Laws of Motion
Sir Isaac Newton was Smart!
 Showed that force, mass, and acceleration are related.
 Summarized the motion of objects in three Laws of motion.
 Universal Law of Gravitation explains how the planets stay in orbit around the sun.
Demo—Penny on Card
 What forces keep the coin at rest on the note card?
o Friction?
o Gravity?
o Both?
 Why didn’t the coin fly away with the card?
o Did the coin’s own “stubbornness” prevent it from doing so?
o Or does the card have some intrinsic property that favors its remaining in place?
Demo – Table Cloth
 What forces keep the beaker at rest on the paper towel?
o Friction, gravity, both?
 Why didn’t the beaker fly away with the paper towel?
 Have you seen this before?
o Is it magic, or just demonstrating Newton’s First Law of Motion: The law of Inertia
Newton’s First Law
 Objects at rest will stay at rest and objects in motion will stay in motion in a straight line
unless acted upon by an unbalanced force
 Law of Inertia
 Laziness!
Momentum and Newton’s Law
 Which object is likely to do more damage to a brick wall: a 5kg bowling ball moving at 1 m/sec or a
.01kg bullet moving 1,000 m/sec?
Momentum and Bad TV
 When a person is shot by a bullet on tv, they often fly backwards through a window.
o Does this really happen?
o The person would have to have a mass of less than 1kg!
Momentum and Real TV
 This is more like what would happen—in the best case scenario where the person is on skates and
almost frictionless!
Momentum – The Equation
 p=mxv
o p = momentum
o m = mass
o v = velocity
Momentum and Newton’s Law
 Which object is likely to do more damage to a brick wall: (1) a 5kg bowling ball moving at 1 m/sec
or (2) a .01kg bullet moving 1,000 m/sec?
o p=mxv
o p = 5kg x 1m/s = 5 kg m/s
o p=mxv
o p = .01kg x 1,000m/s = 10kg m/s
Newton’s Second Law
The force on an object is “proportional” to the object’s mass and acceleration.
 f=mxa
 f=force, m=mass, a=acceleration
 A force is a push or pull on an object.
 The more force applied to an object, the more it accelerates.
 The more massive an object is, the more force is needed to move it.
Newton’s Third Law
 For every action there is an equal and opposite reaction.
m1v1 + m2v2 = m1v3 + m2v4

 Conservation of momentum.
Total momentum in a “closed system” doesn’t change.

Hero of Alexandria
 Invented the Hero engine in the 1st century B.C.
 Used a boiler to produce steam.
 The steam traveled through tubes shaped like a pinwheel.
 Escaping steam produced an action-reaction force, causing the sphere to spin in the opposite
direction!
Hero Engine