Newton’s First and Second Laws of Motion 12.2

I. Scientists Aristotle, Galileo and Newton all worked on concepts of force and motion Aristotle, Galileo and Newton all worked on concepts of force and motion Aristotle- incorrectly proposed that force is required to keep an object moving at constant speed, this error held back progress in the study of motion for almost two thousand years. Aristotle- incorrectly proposed that force is required to keep an object moving at constant speed, this error held back progress in the study of motion for almost two thousand years.

Galileo- helped correct misconceptions about force and motion Galileo- helped correct misconceptions about force and motion Concluded that moving objects not subjected to friction or any other force would continue to move indefinitely Concluded that moving objects not subjected to friction or any other force would continue to move indefinitely Newton- built on the work of Galileo and defined force and mass. He introduced his laws of motion in Principia- his book Newton- built on the work of Galileo and defined force and mass. He introduced his laws of motion in Principia- his book

II. Newton’s First Law The state of motion of an object does not change as long as the net force acting on the object is zero The state of motion of an object does not change as long as the net force acting on the object is zero An object at rest remains at rest unless an unblanced force acts on it An object at rest remains at rest unless an unblanced force acts on it ex: kicking a soccer ball ex: kicking a soccer ball Inertia- the tendency of an object to resist a change in motion Inertia- the tendency of an object to resist a change in motion

Upon impact, the test dummy continues forward until it hits something – inertia

III. Newton’s Second Law acceleration = net force = F mass m The acceleration of an object is equal to the net force acting on it divided by the object’s mass The acceleration of an object is equal to the net force acting on it divided by the object’s mass Ex: the more force you apply to throwing a ball the more the ball accelerates Ex: the more force you apply to throwing a ball the more the ball accelerates This law also works on forces in opposite directions This law also works on forces in opposite directions Ex: seatbelts in cars- explain Ex: seatbelts in cars- explain pg 367 Math Practice #1-3

IV. Weight and Mass Weight- the force of gravity acting on an object Weight- the force of gravity acting on an object Weight = mass x acceleration due to gravity (9.8m/s 2 ) mass is a measure of the inertia of an object; weight is a measure of the force of gravity acting on an object mass is a measure of the inertia of an object; weight is a measure of the force of gravity acting on an object

Planet Multiply your weight by: New weight Mercury0.4 Venus0.9 Earth1 Mars0.17 Jupiter2.5 Saturn1.1 Uranus0.8 Neptune1.2 Moon0.17