Name _________________________________
Forces and Newton’s 1st Law of Motion -- Class Notes
Question: A book sits on a tabletop. You give the book a shove and then release it. The book slides across the tabletop,
eventually coming to rest. Why does the book come to rest? Why doesn't it keep going?
• Aristotle’s Answer (~ 400 b.c.)
"A body's natural state is to be _____________________ . The book slides until it
_______________________________________. The harder you push, the farther the book will
move, but it will eventually __________________________ and _____________________ . "
• Galileo's Answer (~ 1600 a.d.)
"If there's no friction, the ball comes to rest on the uphill when the ball reaches its original _____________ .
In the third picture, the ball can never reach its original _____________ , so it will roll _________________."
• Newton’s Answer (~ 1700 a.d.)
"A body's natural state is to be _____________________ or _________________
in a
_____________________________ at _____________________ speed. In short, an object's
natural state is to be at _________________ velocity."
• Summary: Aristotle vs. Newton
Aristotle: "An object's natural state is to be at ________ -- with a few important exceptions,
like clouds, rivers and the moon."
Newton: "No, an object's natural state is to be at ____________ velocity (which could be rest)."
Aristotle: "Objects resist ______________."
Newton: "No, objects resist ____________ in motion."
Aristotle: "The sliding book came to rest because it ________________ the motion."
Newton: "No, the book came to rest because there was an unbalanced __________ acting on the book, namely,
___________. Without this force, the book would continue to move at constant velocity, its natural motion."
{continued}
Newton classnotes, p.2
• Inertia
Newton said that all objects resist change in motion. He called this resistance inertia, after a Greek word
meaning lazy. (You may recall from chemistry that the __________ elements -- aka Nobel Gases -- don't react;
it's like they are lazy.) Another word for inertia is ____________.
** With that background, let's examine Newton's Three Laws of Motion, one at a time. **
NEWTON’S THREE LAWS OF MOTION
1st Law (Law of Inertia) -- A body will move at constant velocity unless acted on by an unbalanced force.
“Famous version”: Objects in motion ________________________________ in motion, objects at rest
________________________________ at rest.
Question: Explain, using Newton's 1st Law, why a book sliding across a table comes to rest if you're not pushing it.
* Remind your teacher to show you: balloon puck, air track, 1st Law videos.
Vocab:
Net Force:
Static Equilibrium:
Dynamic Equilibrium:
Question: An object that is in static equilibrium is moving…
a) at constant non-zero velocity
b) with acceleration c) not at all
Question: An object that is in dynamic equilibrium is moving…
a) at constant non-zero velocity
b) with acceleration c) not at all
Question: If the net force on an object is zero, the object is moving…
a) at constant non-zero velocity
b) with acceleration c) not at all
Question: Next to each picture, write the net force. Show the direction.