AP Humor of the Day What do you get when you cross an elephant and a grape? Elephant grape sine theta

More AP Humor What do you get when you cross an elephant with a mountain climber? You cannot cross an elephant with a mountain climber. A mountain climber is a scalar!

If something is moving, then something MUST be pushing on it. Things don’t move all by themselves! Aristotle

Oh, baloney! Once an object is moving in a straight line, it’s going to keep right on moving, unless it runs into something. That is, of course, as long as there is NO friction! Friction is what slows things down. Galileo

Galileo… Galileo found that, ignoring the effect of the air, all freely falling objects had the SAME acceleration, regardless of their mass or the height from which they were dropped. The Law of Falling Bodies Born in Pisa 1564

Galileo described HOW things moved, but not WHY they moved that way. Galileo wrote, “the present does not seem to be the proper time to investigate the cause of the acceleration of natural motion….” Galileo died in When Isaac Newton, born Christmas day, 1642, began his studies of motion in the second half of the seventeenth century, that statement was no longer appropriate.

Because Galileo had been so effective in describing motion, Newton could turn his attention to dynamics. Dynamics is the study of why an object moves the way it does- why it starts to move instead of remaining at rest, why it speeds up or moves on a curved path, and why it comes to a stop. Newton’s most famous book was “Principia”, published in This book first listed what came to be known as Newton’s Three Laws of Motion

Forces Force: a push or a pull Forces are vectors. ( you push or pull in a direction!) There are Four Fundamental Forces in our universe 1.Gravitational Force 2.Electromagnetic Force 3.Strong Nuclear Force 4.Weak Force

The strongest of these forces is…. The Strong Nuclear Force (it holds the nucleus of all atoms together) The weakest of these forces is…. Gravity

The unit for Force is the Newton, N If someone was pushing on you with one Newton of Force, it wouldn’t hurt much. One Newton of Force is about the same as the weight of a quarter pound hamburger patty.

Inertia Inertia: an object’s resistance to a change in its motion Mass: how you measure inertia unit: kg

Newton’s First Law of Motion: “The Law of Inertia” An object at rest remains at rest unless acted upon by a net external force An object in motion continues that motion unless acted upon by a net external force.

Newton’s First Law of Motion: “The Law of Inertia” An object at rest remains at rest unless a net external force acts on it. An object in motion continues that motion unless a net external force acts on it. Newton’s law of inertia confirmed what Galileo concluded: Once an object is moving, it requires no additional force to keep it moving. It will continue to move in a straight line unless a NET force acts upon it. I knew it first!!

Stupid humor of the day Why did the chicken cross the road? Issac Newton: Chickens at rest tend to stay at rest, chickens in motion tend to cross roads.

( “the granddaddy of all physics equations”!) Second Law

Third Law For every force, there is an equal but opposite force. Action / Reaction forces

For every force, there is an equal but opposite force. Action / Reaction forces

Third Law For every force, there is an equal but opposite force. Action / Reaction forces

For every force, there is an equal but opposite force. Action / Reaction forces

The Action / Reaction forces do NOT act on the same object. I kick the wall (Action) The wall kicks me back (Reaction)

While driving down the road, an unfortunate bug strikes the windshield of a bus. The bug hit the bus and the bus hit the bug. Which of the two forces is greater: the force on the bug or the force on the bus? For every force, there is an EQUAL by opposite force!

A child pulls on a 5.0 kg wagon with a net force of 20.0 N. What is the wagon’s acceleration? m = 5.0 kg F net = 20.0 N a = F net / m a = 20.0 / 5.0 = a = 4 m/s 2

A dog pulling a man on a sled over ice can accelerate the sled at 2 m/s 2. If the sled and man have a combined mass of kg, what was the net force on the sled? m = kg a = 2 m/s 2 F net = ma F net = kg x 2 m/s 2 = 300 N

When released, the lift provides a net force of 6 N on a 2 kg balloon. If it started at rest, how fast will it be moving in 4.0 s? F net = 6 Nm = 2 kg v o = 0t = 4 s v f = ? v f = v o + at, so we need “a”. a = F net / m a = 6 / 2= 3 m/s 2 v f = x 4 v f = 12 m/s

A 1500 kg. car starts from rest and is moving at 10 m/s after 5.0 s. What was the net force on the car? m = 1500 kg V o = 0 V f = 10 m/s t = 5.0 s F net = ? F net = ma, so we need to find the acceleration. v f = v o + at a = ( v f – v o ) / t a = (10 – 0) / 5 = 2 m/s 2 F net = ma F net = 1500 kg x 2 m/s 2 F net = 3000 N

The Calculus connection When Newton first wrote the relationship we call the second law, it was not it the form we use now. Instead, he wrote