1. Forces and Motion

2. Aristotle: Natural Motion: light objects rise, heavy objects fall
Violent Motion: motion contrary to an object’s nature, requires an external force

3. Forces cause velocities
Summary of Aristotle’s view:
Velocity of object is dependent on the size of the external force applied
Forces cause velocities

4. Galileo:
Objects fall at same rate regardless of mass
Ball rolling down a ramp accelerates

5. Galileo’s Thought Experiment
Very smooth ball rolling between 2 smooth ramps:
How far does the ball roll without the 2nd ramp?
Forever, at constant speed

6. Newton’s First Law of Motion (aka Law of Inertia)
Objects at rest tend to stay at rest, objects in motion to stay in motion at the same speed…
unless acted upon by an external force (e.g. friction)

7. Inertia:
property of matter – the tendency of matter to resist change in motion
The greater the mass, the greater its inertia
(e.g. harder to get a grand piano moving from rest, but harder to stop it once it’s moving)

8. Forces cause changes in velocities
Summary of Newton’s view:
Objects moving at constant velocity do not require an external force to maintain the motion.
An external force exerted on an object will cause it to speed up or slow down
Forces cause changes in velocities