Chapter 2 Forces in Motion

Gravity and Motion Chapter 2, Section 1 Aristotle Vs. Galileo

All objects Fall with the Same Acceleration Objects fall to the ground at same rate Acceleration due to gravity = same for all objects All objects accelerate toward earth at a rate of 9.8 meters per second 9.8 m/s/s Using the figure pg 37 Math Break pg 37

Air Resistance Slows Down Acceleration Fluid friction opposes motion of objects Also known as air resistance Amount of air resistance depends on: Size of object Shape of object Pg 38: reading strategy Self Check Figure 3

Acceleration Stops at the Terminal Velocity Net force does not equal 0 = object accelerates downward Air resistance increases as speed of object increases Upward force of air resistance increases until it exactly matches the downward force of gravity This causes net force of 0= Terminal Velocity (Constant Velocity) Pg 38 Figure 4

Free Fall Occurs When There I No Air Resistance Free Fall= No air resistance Free fall can only happen where there is no air In a vacuum In space Pg 39 Figure 5 Pg 39 Concept Mapping

Orbiting Objects Are In Free Fall An orbiting object is going forward and falling- It is falling around the earth Pg 40 Using the figure Figure 7

Projectile Motion The curved path an object follows when thrown Thrown objects and falling objects have the same acceleration Orbiting objects are examples of projectiles Projectile objects have two components- horizontal and vertical Both components are independent of each other

Ch 2 Sec 2: Newton’s Laws of Motion

Newton’s First Law of Motion “An object at rest remains at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force”

First Law Continued Part 1: Objects at Rest Part 2: Object in Motion Object will not move until a push or pull is exerted on them Ex. Plane won’t fly unless pushed by exhaust from engine Part 2: Object in Motion Object will move forever at the same speed and in same direction unless some unbalanced force acts on it Ex. Bumper car stops but you continue to move forward until your seat belt stops you Pg 44 Real – World Connection Pg 44 Apply

First Law Continued Friction: Makes it difficult to observance of the first law on everyday objects Ex. Grass causes a rolling ball to stop Inertia: Tendency of all objects to resist any change in motion Ex. Slide toward side of car when driver makes a sharp turn Mass: Smaller mass has less inertia than object with large mass Ex. Push car vs. bike Pg 45 Self Check

Newton’s Second Law of Motion “The acceleration of an object depends on the mass of the object and the amount of forced applied”

Second Law Continued Part 1: Acceleration Depends on Mass Same force= objects acceleration decreases as its mass increases and its acceleration increases as its mass decreases Ex. Shopping Cart Part 2: Accelerating Depends on Force An objects acceleration: Increases as force increases Decreases as force decreases

Second Law Continued a= F/m F= m X a M= F/a Pg 46 reteaching Pg 47 math break

Newton’s Third Law of Motion “ Whenever one object exerts a force on a second object, the second object exerts and equal and opposite force on the first.”

Newton’s Third Law Continued All forces act in pairs: Actions and Reactions Can occur when there is no motion Ex: Action Force= Body exert force on chair Reaction force= force exerted by the chair that pushed up on your body No movement

Newton’s Third Law Continued Force Pairs Do Not Act on the Same Object Ex. Swimming Action force = exerted on the water by swimmer’s hands and feet Reaction force = exerted on the swimmer’s hands and feet by water The Effect of a Reaction Can be Hard to See The force of gravity between Earth and a falling object is a force pair Pg 49 examples Pg 49 real world connections

Momentum Is a Property of Moving Objects Momentum= Property of a moving object that depends on the object’s mass and velocity P= m X v P= Momentum m=mass V=velocity More momentum= harder to stop or change direction

Momentum Continued Law of Conservation of Momentum: Two or more objects interact, may exchange momentum, but total amount stays the same Ex. Billiards or Bowling Momentum and Newton’s 3rd Law Action force= billiard ball moves Reaction force= stops cue ball’s motion