- Slides: 22
Newton’s Laws of Motion
Newton’s Laws Ø Newton’s First Law • Law of Inertia Ø Newton’s Second Law • Ø Newton’s Third Law • Law of Action and Reaction Ø Law of Universal Gravitation •
Mass Ø …is the amount of “stuff” in an object. Ø …is measured in kilograms. Ø …is the measure of the inertia of an object. Ø Inertia is the natural tendency of a body resist changes in motion.
History of Inertia Ø Aristotle (384 -322 BCE): “…a constant force will yield a constant speed. ” Ø Jean Buridan (1300 -1358): believed that objects stayed in motion because they possessed “impetus” – something inside that makes them continue to move. Ø Galileo Galilei (1564 -1642): challenged the commonly held belief that an object’s motion was the result of continued force. Instead, he viewed uniform motion as being a state just as natural as rest. OK!
Galileo’s Thought Experiments on Motion Ball drop from leaning tower of Pisa Ø Galileo’s Inclined Planes Ø
Force Ø …is a push or pull that changes the velocity of an object. Ø …is a vector quantity. Ø. . . measured in Newtons.
Newton’s First Law of Inertia Ø “A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force. ” Ø The more massive the object, the greater the tendency to keep doing what it is already doing. Ø
Newton’s First Law Ø No mention of chemical composition Ø No mention of terrestrial or celestial realms Ø Net force required when object changes motion Ø Acceleration is the observable consequence of forces acting
Newton’s Second Law The Sum of the Forces acting on a body is proportional to the acceleration that the body experiences SF a S F = (mass) a
Newton’s Third Law Ø Action-Reaction Ø For every action force there is an equal and opposite reaction force
The Law of Gravity Every mass exerts a force of attraction on every other mass. Ø The math… Ø FG = 6. 67 10 -11 N·m 2/kg 2
Gravity Questions Ø Did the Moon exert a gravitational force on the Apollo astronauts? Ø What kind of objects can exert a gravitational force on other objects?
Gravity Questions Ø The constant G is a rather small number. What kind of objects can exert strong gravitational forces? Ø If the distance between two objects in space is doubled, then what happens to the gravitational force between them?
Weight Ø The weight of an object Fg is the gravitational force acting downward on the object. Ø Fg = m g
Tension (Tensile Force) Ø Tension is the force in a string, chain or tendon that is applied tending to stretch it. Ø FT
Normal Force Ø The normal force on an object that is being supported by a surface is the component of the supporting force that is perpendicular to the surface. Ø FN
Coefficient of Friction F Kinetic Friction • F f = m k. F N Ø Static Friction • F f m s. F N Ø In most cases, mk < ms.
On to problems. . .