Transcript The Metric System, Speed, and Acceleration

Force
Chapter 5
Aristotle and Galileo
Aristotle
-all objects require a continual force to
keep moving (a rolling ball slows down
over time)
Galileo
-Realizes the existence of friction
-In space (no friction) a moving object
continues forever.
Isaac Newton (1642 to 1727)
• born the year Galileo
died, 1642.
• Invented calculus
(while living in
seclusion to avoid
the plague)
• Three laws of motion
• Principia
Mathematica
http://en.wikipedia.org/wiki/Image:GodfreyKnell
er-IsaacNewton-1689.jpg
Newton’s Three Law’s of Motion
1. All objects remain at rest or in uniform,
straight-line motion unless acted upon by
an outside force. (inertia)
2. Force = mass X acceleration
3. Every action (force) has an equal and
opposite reaction (force).
The First Law
• All objects remain at rest or in uniform, straightline motion unless acted upon by an outside
force. (inertia)
– Inertia –tendency of an object to remain at rest or in
constant motion.
– mass - measure of inertia.
– Mass and inertia are directly proportional
The First Law
Ball in jar example:
Does it take less force to push the elephant
(ignore friction) on earth or on the moon?
Does it take less
force to move the
elephant if he is
“weightless” in
space?
Inertial Reference Frames
• Non-accelerating (constant velocity)
reference frame
• All laws of physics are identical in all
Inertial Reference Frames
• Cannot tell if you are moving in an Inertial
Reference Frame
Free Body Diagrams
• Only show forces NOT resolved
components
Draw a free body diagram for a box sitting
on a table.
Draw a free body diagram for a box sitting
on a ramp
Draw a free body diagram for a box being
pushed up a ramp
Free Body Diagrams: Ex. 2
A hockey puck slides at constant velocity
across the ice. Which of the following is
the correct free-body diagram?