Forces and Motion

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

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

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

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

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)

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)

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