Forces: Push or pull applied to an object to keep it in motion.
Natural Tendency of Objects: Objects in motion have a tendency to stay in motion unless acted upon by an external force.
Everyday Examples
Chair Example: A chair at rest does not move unless pushed or pulled, illustrating the need for a force to initiate motion.
Striker on Carom Board: When struck, the striker moves and eventually stops due to opposing forces.
Galileo's Perspective
Friction: Introduced as the opposing force that slows down moving objects. Objects do not stop purely due to their natural state; friction plays a significant role.
Smooth Surfaces: Smoothing a surface reduces friction, allowing objects to slide further and emphasizing friction's role in motion.
Experiment Observations
Adding Powder: Demonstrates how a smoother surface reduces friction, making it harder for objects to stop.
Perfectly Smooth Surface: Hypothetical scenario where a perfectly smooth surface would allow an object to keep moving indefinitely, illustrating that without friction, objects would not come to a stop.
Summary of Learnings
Motion and Rest: In the absence of forces, objects naturally either remain at rest or continue in motion.
Force Functions:
Starts Motion: A force is required to initiate movement.
Stops Motion: A force (like friction) is necessary to stop movement.
Changes Direction: A force can alter the trajectory of a moving object.
Conclusion
Galileo's Insight: The revolutionary idea that things in motion stay in motion unless acted upon by an opposing force, which we understand as friction.
Force Definition: Force is essential for changing an object's state of motion, demonstrating the broader concept of acceleration.