PHY 102 1st Edition Outline of Last Lecture I Uniformly Accelerated Motion a Example b Y Intercept II Equations of Motion III Steps of solving kinematic problems IV Graphs of Motion a Constant motion b Uniformly Accelerated Motion Outline of Current Lecture I First law of motion a Newton s first law b Law c Aristotle II Questions III Types of Forces IV Where Aristotle went wrong V Momentum and Inertia Current Lecture I First Law of Motion These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute a Known as Newton s first law even though Galileo discovered it b A body at rest will stay at rest and a body in motion will stay in motion with constant velocity along a straight line i Without acting forces 1 External 2 Frictional ii MISCONCEPTION objects need a constant source of force to keep them in the same state of motion 1 This is only true in the presence of friction c Objects desire rest according to Aristotle i This is why he proposed that angels moved the heavenly bodies 1 Aristotle thought the flight of an arrow was due to the arrow pushing air out of the way and then the air pushing the arrow along in the empty space created d Associated with constant velocity unless acted upon by an outside force II Questions a When an object is moving with a fixed velocity is it accelerating NO b When an object is moving with a fixed speed is it accelerating MAYBE If there is a change in direction yes c If a car is moving at a constant speed of 60 mph as it turns a corner is it accelerating YES III Types of forces a External someone pushing a ball forward b Friction road against the tires of a car or bearings in a car c Sound is a loss of energy into the air will cause the object to slow down IV Where Aristotle went wrong a Like rest motion is a natural state for a body not experiencing friction b A projectile is not left behind beause it has forward motion of its own c The air is carried along with the spinning earth d The state of physics knowledge in early times was comparatively limited e When something is moving forward it shares in the forward motion i Tossing a pen in an airplane ii Objects inside of a car f Projectile motion i When a plane releases a bomb the bomb shares in the forward motion of plane ii Must accommodate for the forward motion when releasing a projectile V Momentum and Inertia a Momentum p is a vector quantity associated with both mass arbitrarily defined velocity i P mv units typically kg m s ii The momentum of an object at rest is zero b Inertia should not be confused with momentum inertia is a body s tendency to resist changes in motion non mathematical c normal force force of the surface upwards on the object VI Objects at rest a Can have an acceleration i Throwing an object in the air its speed reaches 0 but gravity 9 81 m s 2 is still applied b Inertia is proportional to the mass NOT a numerical value i Only associated with mass ii Ability to resist a change in motion iii If something is more massive it has more inertia c Does the weight of the object at rest change Yes The mass is constant but the force of gravity upon it changes